MEMCAL 


Gift  of  the 

Panama-Pac  if ic   Internat 
exposition  Company 


MANUAL 


OF 


CHEMISTRY. 


A  GUIDE  TO  LECTURES  AND  LABORATORY  WORK  FOR  BEGINNERS 

IN  CHEMISTRY.     A  TEXT-BOOK  SPECIALLY  ADAFfED  FOR 

STUDENTS  OF  MEDICINE,  PHARMACY,  AND 

DENTISTRY. 

BY 

W.  J>IMON,    PH.D.,   M.D., 

PROFESSOR   OF  CHEMISTRY  IN  THE  COLLEGE  OF  PHYSICIANS  AND  SURGEONS  OF  BALTIMORE,   AND  IN 

THE    BALTIMORE    COLLEGE  OF   DENTAL  SURGERY;    EMERITUS  PROFESSOR  IN   THE  MARYLAND 

COLLEGE  OF  PHARMACY,   DEPARTMENT  OF  THE  UNIVERSITY   OF  MARYLAND. 

AND 

DANIEL   BASE,   PH.D., 

PROFESSOR    OF    CHEMISTRY     IN    THE     MARYLAND    COLLEGE    OF     PHARMACY,    DEPARTMENT    OF    THE 
UNIVERSITY    OF    MARYLAND,    AND  OF  ANALYTICAL    CHEMISTRY   IN    THE   DEPART- 
MENT OF  MEDICINE,    UNIVERSITY   OF  MARYLAND,   BALTIMORE. 

TENTH   EDITION,   THOROUGHLY   REVISED. 

WITH  EIGHTY-TWO  ILLUSTRATIONS,  ONE  COLORED  SPECTRA   PLATE, 

AND 

EIGHT  COLORED  PLATES  REPRESENTING  SIXTY-FOUR  CHEMICAL 

REACTIONS. 


LEA   &   FEBIGEK, 
PHILADELPHIA   AND    NEW   YORK. 
1912. 


Copyright,  1912,  by 
LEA  &   FEBIGER. 


Authority  to  use  for  comment  the  Pharmacopoeia  of  the  United  States 
of  America  (Eighth  Decennial  Revision),  in  this  volume,  has  been  granted 
by  the  Board  of  Trustees  of  the  United  States  Pharmacopceial  Convention ; 
which  Board  of  Trustees  is  in  no  way  responsible  for  the  accuracy  of  any 
translations  of  the  Official  Weights  and  Measures,  or  for  any  statement  as 
to  strength  of  Official  Preparations. 


555 


PREFACE  TO  THE  TENTH  EDITION. 


IN  this  new  edition  the  Manual  preserves  the  plan  and  characteristics 
that  have  won  for  it  the  degree  of  approval  shown  in  the  exhaustion  of 
the  nine  previous  issues,  each  in  several  large  printings.  Numerous 
additions  have  been  made,  most  of  which  are  of  fundamental  importance, 
and  again  bring  the  Manual  abreast  of  modern  thought  in  chemistry  to 
its  date  of  issue.  They  embrace  articles  on  the  following  subjects: 
Exothermic  and  endothermic  reactions ;  reversible  reactions  and  chemical 
equilibrium ;  mass  action ;  extension  of  the  articles  on  acids  and  bases ; 
thermochemistry;*  a  new  chapter  on  solution,  in  which,  among  other 
matters,  the  solution  of  gases  and  Henry's  law,  freezing-points,  boiling- 
points  and  osmotic  pressure,  Raoult's  law  and  the  laws  of  osmotic  pres- 
sure are  discussed,  and  the  existence  of  ions  foreshadowed ;  a  new  chapter 
on  the  theory  of  electrolytic  dissociation,  in  which  are  considered  the 
origin  of  the  theory,  ionic  equilibrium,  ionization  of  acids,  bases,  and 
salts,  reactions  on  the  ionic  basis,  activity  of  acids  and  bases,  hydrolysis 
of  salts,  neutralization,  electrolysis  and  Faraday's  laws,  etc. ;  electrolytic 
solution  tension  of  metals ;  principle  of  the  storage-battery ;  and  ionic 
explanation  of  the  action  of  indicators.  Ionic  relations  are  discussed  in 
practically  every  chapter  on  acids  and  the  metals,  and  a  number  of 
compounds  have  been  added  to  the  sections  on  inorganic  and  organic 
chemistry.  Many  of  these  are  of  medical  interest,  for  example,  sodium 
cacodylate,  atoxyl  and  salvarsan,  phenolphthalein,  fluorescein,  phenol- 
sulphonephthalein. 

The  section  on  physiological  chemistry  has  been  rewritten  and  brought 
in  line  with  present-day  knowledge  and  theories.  A  table  of  inter- 
national atomic  weights  on  the  'oxygen  =  16  basis  has  been  added  to 
the  U.  S.  P.  table  of  weights  on  the  hydrogen  =  1  basis. 

It  is  hoped  that  with  these  alterations  and  additions  the  Manual  will 
fully  accomplish  its  object,  viz.,  to  furnish  to  the  student  in  concise  form  a 
clear  presentation  of  the  science,  an  intelligent  discussion  of  those  substances 
which  are  of  interest  to  him,  and  a  trustworthy  guide  to  his  work  in  the 
laboratory. 

As  heretofore,  the  subject  has  been  divided  into  seven  parts,  each  one 
of  which  contains  so  much  of  the  matter  under  consideration  as  is  believed 
to  be  necessary  for  a  fair  understanding  of  the  subject.  At  the  same  time 
care  has  been  taken  to  place  in  the  foreground  all  facts  and  data  which 
are  of  direct  interest  to, the  physician,  pharmacist,  and  dentist. 

iii 


865 


'/ 


iv  PREFACE  TO   THE  TENTH  EDITION. 

In  the  first  part,  treating  of  chemical  physics,  the  student  finds  a  brief 
discussion  of  those  physical  conditions  of  matter  which  have  a  close  rela- 
tionship to  chemical  phenomena,  and  also  of  the  principles  which  lead  to 
an  understanding  of  many  of  the  instruments,  such  as  the  spectroscope, 
polariscope,  etc.,  which  he  uses  in  his  chemical  operations. 

The  second  part  treats  of  those  principles  of  chemistry  which  are  the 
foundation  of  the  science,  and  enters  briefly  into  a  discussion  of  theoretical 
views  regarding  the  constitution  of  matter.  Though  the  authors  prefer 
to  present  these  theories  to  their  classes  at  the  proper  times  during  the 
course  of  lectures,  they  do  not  deem  it  desirable  to  have  them  scattered 
throughout  the  work,  believing  it  better  to  assemble  them  compactly  in 
print,  so  that  the  student  may  be  able  to  study  them  after  having  acquired 
some  knowledge  of  chemical  phenomena. 

The  third  and  fourth  parts  are  devoted  to  the  consideration  of  the  non- 
metallic  and  metallic  elements  and  their  compounds.  While  the  periodic 
law  furnishes  a  most  admirable  basis  for  a  scientific  classification  of  ele- 
ments, yet  their  consideration  according  to  a  strict  adherence  to  periodicity 
does  not  seem  advisable  in  this  book.  For  this  reason  the  old  classifica- 
tion of  metals  and  non-metals,  organic  and  inorganic  compounds  has  been 
retained,  since  experience  has  shown  it  to  be  well  adapted  for  the  instruc- 
tion of  beginners  in  chemistry. 

The  fifth  part  is  devoted  to  analytical  chemistry  and  will  serve  the 
student  as  a  guide  in  his  laboratory  work.  Qualitative  methods  are 
chiefly  considered,  but  a  chapter  is  added  giving  official  methods  for 
volumetric  determinations. 

The  sixth  part  treats  of  organic  chemistry.  Though  it  is  impossible  to 
include  within  the  limits  of  this  text-book  an  extended  consideration  of  a 
branch  of  chemical  science  so  highly  developed,  yet  it  is  believed  that  an 
intelligent  study  of  this  part  will  familiarize  the  student  with  carbon 
compounds  sufficiently  to  give  him  a  clear  understanding  of  their  general 
character,  and  a  knowledge  of  the  bodies  which  are  most  important  in 
medical  science. 

The  seventh  and  last  part  gives  the  principal  facts  of  physiological 
chemistry.  Special  care  has  been  taken  also  to  introduce  here  the  most 
modern  methods  for  chemical  examination  in  clinical  diagnosis. 

The  authors  will  be  grateful  for  any  suggestions  looking  to  the  im- 
provement of  the  book. 

The  authors  wish  to  express  here  their  obligations  to  G.  Howard 
White,  Jr.,  M.  D.,  by  whom  the  section  on  physiological  chemistry  was 
rewritten. 

W.   S. 

D.   B. 

BALTIMORE,  1912. 


CONTENTS. 


i. 

CHEMICAL  PHYSICS. 

PAGE 

1.  Fundamental  properties  of  matter. 

Matter — Extension — Solid  state — Force — Energy — Crystal- 
lization— Liquid  and  gaseous  state — Divisibility — Molecular 
theory — Gravitation — Weight — Specific  weight — Weight  of 
gases — Barometer — Surface-action — Adhesion — Capillary  at- 
traction— Absorption — Diffusion  —  Osmose — Indestructibility  17-42 

2.  Heat. 

Motion  of  molecules — Latent  heat — Sources  of  heat — Heat 
effects — Thermometers — Absolute  zero  and  absolute  tempera- 
ture— Mechanical  equivalent  of  heat — Specific  heat — Conduc- 
tion, Convection,  and  radiation — Melting,  boiling,  and  evapo- 
ration    43-55 

3.  Light. 

Light  a  form  of  energy — Reflection — Refraction — Prisms — 
Dispersion — The  spectroscope — Bright  line  spectra — Absorp- 
tion spectra — Double  refraction — Polarization — The  polari- 
scope — Chemical  effects  of  light 56-68 

4.  Electricity. 

Electricity  generated  by  friction — Conductors  and  non- 
conductors— Duality  of  Electricity — Induction — Electrical 
machines — Static  electricity — Magnetism — Electricity  gener- 
ated by  chemical  action — Galvanic  cells — Current  electricity 
—  Electromotive  force  —  Electric  units  —  Electromagnets  — 
Electricity  generated  by  magnetism — Voltaic  induction — In- 
duction coil — Conversion  of  electric  energy  into  heat,  light, 
and  chemical  action — Electric  furnace  —  Electric  spark — 
Cathode  ray — Rontgen  rays — Radio-activity 69-86 

II. 
PRINCIPLES   OF  CHEMISTRY. 

5.  Element,  compound,   chemical  affinity,  modes  of  effecting 

chemical  change. 

Decomposition  by  heat — Elements — Compound  substances — 
Decomposition  by  electricity,  by  light,  and  by  mutual  action 
of  substances  upon  each  other — Physical  phenomena  accom- 
panying chemical  action — Chemical  or  internal  energy — Ex- 
othermic and  endothermic  actions — Chemical  affinity  ....  87-93 

6.  Laws  and  theories  of  chemistry. 

Law  of  the  constancy  of  composition — Law  of  multiple 

(v) 


vi  CONTENTS. 

PAGE 

proportions — Combining  weights  of  elements — Atomic  theory 
— Atomic  weight — Atoms  and  molecules — Chemical  symbols — 
Formulas  of  compounds — Law  of  chemical  combinations  by 
volume — Law  of  equivalents — Valence  or  quantivalence  .  .  .  93-104 

7.  Determination  of  atomic  and  molecular  weights. 

Determination  of  atomic  weights  by  chemical  decomposition, 
by  means  of  specific  weights  of  gases  or  vapors,  by  means  of  spe- 
cific heat — Determination  of  molecular  weights — Raoult's  law  105-110 

8.  Chemical  equations.    Types  of  chemical  change.    Reversible 

actions  and  chemical  equilibrium.  Mass  action. 
Acids,  bases,  neutralization,  salts.  Radical.  Consti- 
tutional formulas  ..." 110-124 

9.  General  remarks  regarding  elements. 

Relative  importance  of  different  elements — Classification  of 
elements — Metals  and  non-metals — Natural  groups  of  elements 
— MendelejefF's  periodic  law — Physical  properties  of  elements 
— Allotropic  modifications — Relationship  between  elements 
and  the  compounds  formed  by  their  union — Nomenclature — 
How  to  study  chemistry 124-133 

III. 
NON-METALS  AND  THEIR  COMBINATIONS. 

Symbols,  atomic  weights,  and  derivation  of  names — Occur- 
rence in  nature — Time  of  discovery — Valence 135-136 

10.  Oxygen. 

History — Occurrence  in  nature — Preparation — Physical  and 
chemical  properties — Combustion — Ozone — Thermo-chemistry  137-144 

11.  Hydrogen.    Water.    Hydrogen  dioxide. 

History — Occurrence  in  nature — Preparation — Properties — 
Nascent  state — Water — Mineral  waters — Drinking-water — Dis- 
tilled water — Analysis  and  synthesis — Explanation  of  efflor- 
escence and  deliquescence — Hydrogen  dioxide 144-156 

12.  Solution. 

General  remarks — Terms  employed — Heat  of  solution — So- 
lution of  gases — Henry's  law — Freezing-points,  boiling-points, 
and  osmotic  pressure  of  solutions — Raoult's  law — Laws  of  os- 
motic pressure 157-164 

13.  Nitrogen. 

Occurrence  in  nature — Preparation — Properties — Atmo- 
spheric air — Argon — Helium — Ammonia — Hydrazine— Hy- 
droxylamine — Triazoic  acid — Compounds  of  nitrogen  and 
oxygen — Nitrogen  monoxide— Nitric  acid  ;  tests  for  it  ...  164-177 

14.  Carbon.    Silicon.    Boron. 

Occurrence  in  nature — Properties — Diamond — Graphite — 
Tests  for  carbon — Carbon  dioxide — Carbonic  acid — Tests  for 
carbonic  acid — Carbon  monoxide — Carbonyl  chloride — Com- 
pounds of  carbon  and  hydrogen — Flame — Silicon — Silicic  acid 


CONTENTS.  vii 

PAGE 

— Carborundum — Boron,  boric  acid;  tests  for  it — Sodium  per- 
borate         178-189 

15.  Theory  of  electrolytic  dissociation,  or  ionization,  etc. 

Theory  of  electrolytic  dissociation — Composition  of  ions — 
Ions  and  atoms  not  the  same — Symbols  representing  ions — 
Ionic  equilibrium.  Ionization  constant — Effects  of  ionic  equi- 
librium in  chemical  reactions — Precipitation — Electrolysis — 
Secondary  changes  in  electrolysis — Faraday's  laws — Conduc- 
tivity— Electromotive  force  required  in  electrolysis — Electro- 
chemical series  of  the  metals — Acids — Independence  of  ions — 
Analytical  reactions  or  tests — Kinds  of  ions  formed  by  acids — 
Activity  or  "  strength  "  of  acids — Bases — Salts — Acid  and  basic 
salts — Hydrolysis  of  salts — Neutralization — Heat  of  neutrali- 
zation— Degree  of  dissociation  of  common  substances  ....  189-203 

16.  Sulphur.    Selenium.    Tellurium. 

Occurrence  in  nature — Properties — Crude,  sublimed,  washed, 
and  precipitated  sulphur — Sulphur  dioxide — Sulphurous  acid  ; 
tests  for  it — Sulphur  trioxide — Sulphuric  acid  :  its  manufac- 
ture, properties,  and  ions — Tests  for  sulphates — Sulphur  acids 
— Pyrosulphuric  acid — Thiosulphuric  acid — Hydrogen  sul- 
phide ;  tests  for  it — Ions  of  hydrogen  sulphide  and  its  salts — 
Use  of  it  in  analysis — Carbon  disulphide — Selenium — Tellu- 
rium— Ionic  mechanism  of  the  solution  by  acids  of  salts  that 
are  insoluble  in  water 204-219 

17.  Phosphorus. 

Occurrence  in  nature — Manufacture,  properties,  and  modi- 
fications— Poisonous  properties  and  detection  in  cases  of  pois- 
oning— Oxides  of  phosphorus — Hypophosphorous  acid  ;  tests 
for  it — Phosphorous  acid  ;  tests  for  it — Metaphosphoric,  pyro- 
phosphoric,  orthophosphoric  acids;  tests  for  them — Ions  of 
phosphoric  acid  and  its  salts — Hydrogen  phosphide — Phos- 
phorus tri-  and  pentachloride 219-229 

18.  Chlorine. 

Halogens — Occurrence  in  nature,  preparation,  and  proper- 
ties of  chlorine— Chlorine  water — Hydrochloric  acid ;  tests  for 
it — Nitrohydrochloric  acid — Compounds  of  chlorine  with  oxy- 
gen— Hypochlorous  acid — Hypochlorites — Solution  of  chlor- 
inated soda— Chloric  acid ;  tests  for  it— Perchloric  acid  .  .  .  230-238 

19.  Bromine.    Iodine.    Fluorine. 

Bromine — Hydrobromic  acid — Tests  for  bromides — Hypo- 
bromous  and  bromic  acid — Iodine — Hydriodic  acid — Tests  for 
iodine  and  iodides — lodic  acid — Sulphur  iodide — Compounds 
of  iodine  with  bromine  and  chlorine — Compounds  of  nitrogen 
with  halogens — Fluorine — Hydrofluoric  acid 239-245 


viii  CONTENTS. 

IV. 

METALS  AND  THEIR   COMBINATIONS. 

PAGE 

20.  General  remarks  regarding  metals. 

Derivation  of  names,  symbols,  and  atomic  weights — Melting- 
points,  specific  gravities,  time  of  discovery,  valence,  occur- 
rence in  nature,  classification,  and  general  properties  of  metals 
— Alloys,  their  manufacture  and  properties 217-255 

21.  Potassium. 

General  remarks  regarding  the  alkali  metals — Occurrence  in 
nature — Potassium  hydroxide,  oxide,  carbonate,  bicarbonate, 
percarbonate,  nitrate,  chlorate,  sulphate,  sulphite,  hypophos- 
phite,  iodide,  bromide — Analytical  reactions 255-262 

22.  Sodium.    Lithium.    Caesium.    Rubidium. 

Occurrence  in  nature — Sodium  chloride,  hydroxide,  perox- 
ide, carbonate,  bicarbonate,  sulphate,  sulphite,  thiosulphate, 
phosphate,  nitrate,  borate — Analytical  reactions — Lithium — 
Caesium— Rubidium 262-268 

23.  Ammonium. 

General  remarks — Ammonium  ion — Ammonium  chloride, 
carbonate,  sulphate,  nitrate,  phosphate,  iodide,  bromide,  and 
sulphide — Analytical  reactions — Summary  of  analytical  char- 
acters of  the  alkali-metals 268-272 

24.  Magnesium. 

General  remarks — Occurrence  in  nature — Metallic  magne- 
sium— Magnesium  carbonate,  oxide,  sulphate,  nitride — Re- 
marks on  tests  for  metals — Analytical  reactions 272-276 

25.  Calcium.    Strontium.    Barium.    Radium. 

General  remarks  regarding  alkaline  earths — Occurrence  in 
nature — Calcium  oxide,  hydroxide,  carbonate,  sulphate,  phos- 
phate, acid  phosphate,  and  hypophosphite — Bone-black  and 
bone-ash — Chlorinated  lime,  calcium  chloride  and  bromide — 
Sulphurated  lime — Calcium  carbide — Analytical  reactions  and 
ionic  equations  for  calcium — Barium  and  strontium  ;  their  salts 
and  analytical  reactions — Radium — Summary  of  analytical 
characters  of  the  alkaline-earth  metals 277-285 

26.  Aluminum.    Cerium. 

Occurrence  in  nature — Metallic  aluminum — Alum — Alumi- 
num hydroxide,  oxide,  sulphate,  and  chloride — Ionic  equations 
— Clay — Glass — Cement — Ultramarine — Analytical  reactions 
— Cerium — Summary  of  Analytical  characters  of  the  earth- 
metals  and  chromium 285-292 

27.  Iron. 

General  remarks  regarding  the  metals  of  the  iron  group — 
Occurrence  in  nature — Manufacture  of  Iron — Properties — 
Reduced  iron — Ferrous  and  ferric  oxides,  hydroxides,  and 
chlorides — Dialyzed  iron — Ferrous  iodide,  bromide,  sulphide, 


CONTENTS.  ix 

PAGE 

and  sulphate — Ferric  sulphate  and  nitrate — Ferrous  carbonate, 
phosphate,  and  hypophosphite — Analytical  reactions — Ions  of 
iron 292-302 

28.  Manganese.    Chromium.    Cobalt.    Nickel. 

[Manganese ;  its  oxides,  sulphate,  and  hypophosphite — Po- 
tassium permanganate — Manganese  reactions — Ions  of  man- 
ganese compounds  —  Chromium  —  Potassium  dichromate — 
Chromium  trioxide — Ions  of  chromates  and  dichromates — 
Chromic  oxide  and  hydroxide — Perchromic  Acid — Reactions 
for  chromium  compounds — Cobalt  and  nickel 303-312 

29.  Zinc.    Cadmium. 

Occurrence  in  nature — Metallic  zinc — Zinc  oxide,  chloride, 
oxychloride,  oxyphosphate,  bromide,  iodide,  carbonate,  sul- 
phate— Analytical  reactions — Ions  of  zinc — Antidotes — Cad- 
mium— Summary  of  analytical  characters  of  metals  of  the  iron 
group 312-318 

30.  Lead.    Copper.    Bismuth. 

General  remarks  regarding  the  metals  of  the  lead  group — 
Lead — Electrolytic  solution  tension — Lead  oxides — Storage 
battery — Lead  nitrate,  carbonate,  iodide — Poisonous  proper- 
ties of  lead — Antidotes — Lead  reactions — Copper — Cupric  and 
'  cuprous  oxide — Cupric  sulphate  and  carbonate — Ammonio- 
copper  compounds — Poisonous  properties  and  antidotes — 
Copper  reactions — Bismuth — Bismuth  subnitrate  and  subcar- 
bonate — Bismuth  reactions —  .  .  .  318-330 

31.  Silver.    Mercury. 

Silver — Silver  nitrate — Photography — Silver  oxide — Anti- 
dotes— Complex  silver  compounds— Silver  reactions — Ions  of 
silver — Mercury — Amalgams — Mercurous  and  mercuric  ox- 
ides, chlorides,  iodides,  sulphates,  nitrates,  sulphides — Am- 
moniated  mercury — Antidotes — Mercury  reactions — Ions  of 
mercury  compounds — Summary  of  analytical  characters  of 
metals  of  the  lead  group 330-346 

32.  Arsenic. 

General  remarks  regarding  the  metals  of  the  arsenic  group 
— Arsenic — Arsenous  and  arsenic  oxides  and  acids — Sodium 
arsenate — Lead  arsenate — Hydrogen  arsenide — Sulphides  of 
arsenic — Arsenous  iodide — Analytical  reactions — Ions  of  ar- 
senous  and  arsenic  acids — Preparatory  treatment  of  organic 
matter  for  arsenic  analysis — Antidotes , 346-358 

33.  Antimony.    Tin.    Gold.    Platinum.    Iridium.    Molybdenum. 

Antimony — Trisulphide  and  pentasulphide  of  antimony — 
Antimonous  chloride  and  oxide — Antidotes — Antimony  reac- 
tions— Tin — Stannous  and  stannic  hydroxide  and  chloride — 
Metastannic  acid — Tin  reactions— Gold — Refining  gold— Gold 
chloride— Platinum  —  Iridium  —  Molybdenum  —  Summary  of 
analytical  characters  of  metals  of  the  arsenic  group 358-369 


X  CONTENTS. 

V. 

ANALYTICAL  CHEMISTRY. 

PAGE 

34.  Introductory  remarks  and  preliminary  examination. 

General  remarks — Apparatus  needed  for  qualitative  analysis 
— Reagents  needed — General  mode  of  proceeding  in  qualitative 
analysis — Use  of  reagents — Preliminary  examination — Physi- 
cal properties — Action  on  litmus — Heating  on  platinum  foil 
Heating  on  charcoal  alone  and  mixed  with  sodium  carbonate 
— Flame-tests — Colored  borax-beads — Liquefaction  of  solid 
substances — Table  I.:  Preliminary  examination 371-381 

35.  Separation  of  metals  into  different  groups. 

General  remarks — Group  reagents — Acidifying  the  solution 
— Addition  of  hydrogen  sulphide — Separation  of  the  metals  of 
the  arsenic  group  from  those  of  the  lead  group — Addition  of 
ammonium  sulphide  and  ammonium  carbonate — Table  II. : 
Separation  of  metals  into  different  groups 382-387 

36.  Separation  of  the  metals  of  each  group. 

Table  III. :  Treatment  of  the  precipitate  formed  by  hydro- 
chloric acid — Treatment  of  the  precipitate  formed  by  hydrogen 
sulphide — Table  IV. :  Treatment  of  that  portion  of  the  hydro- 
gen sulphide  precipitate  which  is  insoluble  in  ammonium  sul- 
phide— Table  V.  :  Treatment  of  that  portion  of  hydrogen 
sulphide  precipitate  which  is  soluble  in  ammonium  sulphide 
— Table  VI. :  Treatment  of  the  precipitate  formed  by  ammo- 
nium hydroxide  and  sulphide — Table  VII. :  Treatment  of  the 
precipitate  formed  by  ammonium  carbonate — Table  VIII. : 
Detection  of  the  alkalies  and  of  magnesium 387-390 

37.  Detection  of  acids. 

General  remarks — Detection  of  acids  by  means  of  the  action 
of  strong  sulphuric  acid — Table  IX. :  Preliminary  examina- 
tion for  acids — Detection  of  acids  by  means  of  reagents  added 
to  their  neutral  or  acid  solution — Table  X. :  Detection  of  the 
more  important  acids  by  means  of  reagents  added  to  the  solu- 
tion— Table  XI. :  Systematically  arranged  table,  showing  the 
solubility  and  insolubility  of  inorganic  salts  and  oxides — 
Table  XII. :  Table  of  solubility— Special  remarks 391-401 

38.  Methods  for  quantitative  determinations. 

General  remarks  —  Gravimetric  methods  —  Volumetric 
methods — Standard  solutions — Normal  solutions — Different 
methods  of  volumetric  determination — Indicators  and  ionic 
explanation  of  their  action — Titration — Acidimetry  and  alka- 
limetry— Normal  acid  and  alkali  solution — Oxidimetry — Po- 
tassium permanganate  and  dichromate — lodimetry — Solutions 
of  iodine,  sodium  thiosulphate,  bromine,  silver  nitrate,  sodium 
chloride,  and  potassium  sulphocyanate — Gas  analysis — Water 
analysis 402-432 


CONTENTS.  xi 

PAGE 

39.  Detection  of  impurities  in  official  inorganic  chemical  prep- 

arations. 

General  remarks — Official  chemicals  and  their  purity — Tests 
as  to  identity— Qualitative  tests  for  impurities — Quantitative 
tests  for  the  limit  of  impurities 433-437 

VI. 

CONSIDERATION   OF   CARBON  COMPOUNDS,   OR  ORGANIC 

CHEMISTRY. 

40.  Introductory  remarks.    Elementary  analysis, 

Definition  of  organic  chemistry — Elements  entering  into  or- 
ganic compounds — General  properties  of  organic  compounds 
— Difference  in  the  analysis  of  organic  and  inorganic  substances 
— Qualitative  analysis  of  organic  substances — Ultimate  or 
elementary  analysis — Determination  of  carbon,  hydrogen, 
oxygen,  nitrogen,  sulphur,  and  phosphorus — Determination  of 
atomic  composition  from  results  obtained  by  elementary 
analysis — Empirical  and  molecular  formulas — Rational,  con- 
stitutional, structural,  or  graphic  formulas 439-448 

41.  Constitution,  decomposition,  and  classification  of  organic 

compounds. 

Radicals  or  residues — Chains — Homologous  series — Sub- 
stitution— Derivatives  —  Isomerism  —  Metamerism  — Polymer- 
ism — Stereo-isomerism — Various  modes  of  decomposition — 
Action  of  heat  upon  organic  substances — Dry  or  destructive 
distillation — Action  of  oxygen  upon  organic  substances — 
Combustion — Decay — Fermentation  and  putrefaction — Anti- 
septics, disinfectants,  and  deodorizers — Action  of  chlorine,  bro- 
mine, nitric  acid,  alkalies,  dehydrating  and  reducing  agents 
upon  organic  substances — Classification  of  organic  compounds  448-462 

42.  Hydrocarbons.    Haloid  derivatives. 

Occurrence  in  nature — Formation  of  hydrocarbons — Prop- 
erties— Paraffin  or  methane  series — Methane — Ethane — Coal 
— Natural  gas — Coal-oil,  petroleum — Illuminating  gas — Coal- 
tar — Unsaturated  hydrocarbons — Olefines — Ethylene — Amyl- 
ene  —  Acetylene  —  Halogen  derivatives  of  hydrocarbons  — 
Methyl  chloride— Dichlor-  and  Tetrachlor-methane— Chloro- 
form— Bromoform — lodoform — Ethyl  chloride,  bromide,  and 
iodide — Compounds  of  alkyl  radicals  with  other  elements — 
Sodium  cacodylate 462-478 

43.  Alcohols. 

Constitution  of  alcohols — Occurrence  in  nature — Formation 
and  properties  of  alcohols — Monatomic  normal  alcohols — 
Methyl  alcohol— Ethyl  alcohol— Denatured  alcohol— Alcoholic 
liquors — Wines,  beer,  spirits — Amyl  alcohol — Allyl  alcohol — 
Glycerin  —  Glycerin  trinitrate  —  Dynamite  —  Glycerin-phos- 
phoric acid 479-489 


xii  CONTEXTS. 

PAGE 

44.  Aldehydes.    Ketones. 

Aldehydes — Formic  aldehyde— Formalin — Acetic  aldehyde 
— Paraldehyde — Trichloraldehyde — Hydrated  chloral — Acrylic 
aldehyde — Ketones — Acetone — Sulphur  derivatives — Sulpho- 
nal— Trional— Tetronal 489-496 

45.  Monobasic  fatty  acids. 

General  constitution  of  organic  acids — Occurrence  in  nature 
— Formation  of  acids— Properties — Fatty  acids — Formic  acid 
— Acetic  acid — Vinegar — Reactions  for  acetates— Acetate  of 
potassium,  sodium,  zinc,  iron,  lead,  and  copper — Trichlor- 
acetic  acid— Acetyl  chloride — Acetic  anhydride — Butyric  acid 
— Valeric  acid  and  its  salts— Stearic  acid — Oleic  acid — Disso- 
ciation of  formic  acid  and  its  homologues 496-507 

46.  Polybasic  and  hydroxy-acids. 

Oxalic  acid,  oxalates,  and  analytical  reactions — Glycolic 
acid — Lactic  acid — Malic  acid — Tartaric  acid  ;  analytical  re- 
actions— Potassium  tartrate— Potassium-sodium  tartrate — An- 
timony-potassium tartrate— Action  of  certain  organic  acids 
upon  certain  metallic  oxides — Scale  compounds — Citric  acid  ; 
analytical  reactions — Citrates 508-518 

47.  Ethers  and  esters. 

Constitution— Formation  of  ethers — Occurrence  in  nature — 
General  properties — Ethyl  ether — Acetic  ether — Ethyl  nitrite 
— Amyl  nitrite— Fats  and  fat  oils — Soap — Lanolin 518-527 

48.  Carbohydrates. 

Constitution — Properties — Occurrence  in  nature — Classifica- 
tion — Monosaccharides — Dextrose  ;  tests  for  it — Levulose — 
Galactose  —  Inosite  —  Disaccharides  —  Cane-sugar  —  Maltose — 
Lactose — Polysaccharides — Starch  —  Dextrin  —  Gums  —  Cellu- 
lose—Pyroxylin— Collodion — Glycogen — Glucosides 528-539 

49.  Compounds  containing  nitrogen. 

Derivatives  of  nitric  acid — Nitro,  nitroso,  and  isonitroso 
compounds — Ammonia  derivatives — Amines— Poly-amines — 
Amino-acids  —  Amino-acetic  and  amino-formic  acid  —  Ure- 
thanes  —  Ethyl  carbamate  —  Sarcosine  —  Cystine  —  Leucine — 
Taurine — Aspartic  acid,  asparagine — Guanidine— Creatine — 
Urea — Ureids— Veronal — Cyanogen  compounds — Hydrocyanic 
acid — Dissociation  of  cyanogen  compounds — Cyanides  of  po- 
tassium, silver,  and  mercury— Cyanogen  derivatives  obtained 
from  atmospheric  nitrogen — Cyanic  acid — Metallocyanides — 
Potassium  ferrocyanide  and  ferri cyanide— Sodium  nitroferri- 
cyanide — Nitriles  and  isocyanides— Iso-sulpho-cyanides  — 
Myronic  acid — Allyl  mustard  oil 539-557 

50.  Benzene  series.    Aromatic  compounds. 

General  remarks — Constitution — Benzene  series  of  hydro- 
carbons— Benzene — Toluene — Xylenes — Cymene — Amino  com- 
pounds of  benzene — Aniline — Acetanilide — Sulphanilic  acid — 
Diphenyl-amine —  Meta-phenylene-diamine  —  Methylene-blue 


CONTENTS.  xiii 

PAGE 

— Diazo  compounds— Phenyl  hydrazine — Atoxyl — Salvarsan — 
Hydroxyl  derivatives — Phenols — Carbolic  acid — Acetphene- 
tidin — Trinitro-phenol— Phenolsulphonicacid — Cresols— Creo- 
sote— Guaiacol  and  its  compounds — Veratrol — Eugenol — Safrol 
—Thymol  and  the  iodide— Resorcinol — Quinol — Pyrogallol — 
Phloroglucinol  —  Aromatic  alcohols  —  Aromatic  aldehydes — 
Benzaldehyde — Oil  of  bitter  almond— Cinnamic  aldehyde — 
Vanillin — Cumarin — Acids  of  the  benzene  series — Benzoic  acid 
— Benzoyl  chloride — Benzosulphinide — Phthalic  acids— Phe- 
nolphthalein— Fluorescein,  Eosin— Phenolsulphonphthalein— 
Salicylic  acid— Aspirin— Salicin— Methyl  salicylate— Phenyl 
salicylate — Gallic  and  tannic  acid — Naphthalene — Naphthol — 
Santonin— Pyrrol — Antipyrine— Pyridine  —  Quinoline  —  Kai- 
rine— Thalline  557-594 

51.  Terpenes  and  their  derivatives. 

Volatile  or  essential  oils— Terpenes — Terebene — Sesquiter- 
penes  —  Rubber  —  Gutta-percha  —  Stearoptenes  —  Camphor — 
Cineol — Menthol — Resins — Balsams — Turpentine 594-599 

52.  Alkaloids. 

General  remarks— Properties— Assay  methods— Antidotes- 
Detection— Classification— The  pyridine  group— Pi  perin— 
Coniine  —  Pilocarpine — Nicotine  —  Sparteine  —  The  tropine 
group — Atropine — Homatropine— Hyoscyarnine  —  Hyoscine — 
Cocaine  and  its  substitutes — The  quinoline  group — Cinchona 
alkaloids — Quinine  and  quinidine— Cinchonine  and  cinchoni- 
dine  —  Strychnine  —  Brucine  —  Veratrine  —  The  isoquinoline 
group — Morphine,  apomorphine — Codeine — Narcotine,  narce- 
ine — Meconic  acid — Hydrastine,  hydrastinine — Berberine — 
The  xanthine  alkaloids — Caffeine — Theobromine — Unclassified 
alkaloids  —  Physostigmine  —  Aconitine  —  Colchicine  — Pto- 
maines ;  their  formation  and  properties — Leucomaines  .  .  .  600-621 

VII. 

PHYSIOLOGICAL  CHEMISTRY. 

53.  Proteins. 

Occurrence  in  nature — General  properties — Classification — 
Simple  proteins  —  Albumins  —  Globulins  —  Glutelins— Prola- 
mines  or  alcohol-soluble  proteins — Albuminoids — Histones — 
Protamines — Conjugated  proteins — Nucleoproteins — Glycopro- 
teins  —  Phosphoproteins  —  Haemoglobins  —  Lecithoproteins — 
Derived  proteins — Proteans— Metaproteins — Coagulated  pro- 
teins— Proteoses — Peptones  —  Peptides  —  Products  of  proteo- 
lysis  —  Tyrosine  —  Leucine — Hydrolysis — Enzymes — Pepsin — 
Pancreatin 623-639 

54.  Chemical  changes  in  plants  and  animals. 

Difference  between  vegetable  and  animal  life — Formation  of 
organic  substances  by  the  plant — Animal  food — Digestibility 


xiv  CONTENTS. 

PAGE 

— Nutrition  —  Digestion  —  Absorption  —  Respiration — AVaste- 
products  of  animal  life — Chemical  changes  after  death     .    .    .     639-649 

55.  Animal  fluids  and  tissues. 

Constituents  of  the  animal  body — Blood ;  its  properties  and 
composition — Blood-plasma  and  blood-serum — Blood-pigments 
—  Fibrin  —  Hemoglobin  —  Haematin  —  Hrematoporphyrin  — 
Spectroscopic  examination — Examination  of  blood-stains — 
Immune  bodies  of  the  blood-serum — Lymph — Bone — Teeth — 
Hair,  nails,  etc. — Muscle — Muscle  extractives — Creatine  and 
Creatinine — Xanthine  bases — Purine  bases — Xanthine  and 
hypoxanthine — Meat-extracts — The  thyroid  gland — Brain — 
Lecithins— Cholesterin 649-671 

56.  Digestion.  , 

General  remarks — Salivary  digestion — Saliva,  tests  for  it — 
Gastric  digestion — Gastric  juice,  its  clinical  examination — 
Intestinal  digestion — Pancreatic  secretions — Bile — Biliary  pig- 
ments, acids,  and  calculi— Fermentative  and  putrefactive 
changes — Absorption,  assimilation — Feces ;  their  chemical  ex- 
amination— The  liver — Glycogen— Indole — Skatole 672-694 

57.  Milk. 

Properties  and  composition — Milk-proteins — Casein — Milk- 
fat — Butter — Lactose  ;  tests  for  it — Changes  in  milk  on  stand- 
ing— Milk  preservatives — Analysis  of  milk — Human  milk — 
Modified  milk 695-703 

58.  Urine  and  its  constituents. 

Excretion  of  urine — General  properties — Points  to  be  con- 
sidered in  the  analysis  of  urine — Color — Odor — Volume — Re- 
action— Specific  gravity — Composition — Normal  and  patho- 
logical constituents — Determination  of  total  solids  and  inor- 
ganic constituents — Nitrogen  in  the  urine — Urea,  its  reactions 
and  determination — Ammonia  in  urine  and  its  determination — 
Creatine  and  creatinine — Uric  acid,  its  tests  and  determination 
— Xanthine  bodies — Allan  torn — Hippuric  acid — Chlorides  and 
their  determination — Phosphoric  acid — Sulphur  compounds  in 
urine — Indican — Phenol — Pyrocatechin— Proteins  in  urine  and 
tests — Blood  and  its  tests — Carbohydrates  and  tests — Deter- 
mination of  dextrose  in  urine — Laevulose,  maltose,  lactose,  and 
pentoses — Glycuronic  acid — Acetone,  diacetic,  and  beta-oxy- 
butyric  acids — Bile — Alkaptonic  acids — Diazo-reaction — Func- 
tional tests  of  the  kidney — Urinary  sediments — Urinary  cal- 
culi 703-746 


APPENDIX. 

Table  of  weights  and  measures 747 

Table  of  elements 749 

Index     ....  751 


LIST    OF   ILLUSTRATIONS. 


FIG.  PAGE 

1.  The  cube 22 

2.  Regular  octahedron 22 

3.  Quadratic  octahedron 23 

4.  Right-square  or  quadratic  prism 23 

5.  Rhombic  octahedron 23 

6.  Double  six-sided  pyramid      23 

7.  Rhombohedron      ." 24 

8.  Six-sided  prism     ...           24 

9.  Monoclinic  double  pyramid      24 

10.  Monoclinic  prism 24 

11.  Triclinic  prism 25 

12.  Triclinic  octahedron 25 

13.  14.  Structure  of  matter 29 

15.  Dialyzer •  .    .        .    .  41 

16.  Thermometric  scales 47 

17.  Reflection 57 

18.  Refraction  by  a  parallel  plate 58 

19.  Refraction  through  a  prism ^ 58 

20.  Prismatic  spectrum 59 

21.  Spectroscope -   •    •    •    •  60 

22.  Direct-vision  spectroscope      61 

23.  Double  refraction 63 

24.  Tourmaline  plates 64 

25.  Undulation  in  a  cord 64 

26.  Explanatory  diagrams  of  the  action  of  tourmaline  plates 65 

27.  Nicol's  prism 66 

28.  Lippich's  polariscope 68 

29.  Daniell's  cell 75 

30.  Induction  coil -  .    .  79 

31.  Electric  furnace '. 80 

32.  Longitudinal  section  of  carborundum  furnace 81 

33.  Exterior  view  of  carborundum  furnace 81 

34.  Electrolysis  of  water 82 

35.  Apparatus  for  the  decomposition  of  mercuric  oxide 87 

36.  Diagram  of  periodic  system  in  spiral  form 130 

37.  Apparatus  for  generating  oxygen 140 

38.  Apparatus  for  generating  hydrogen 146 

39.  Apparatus  for  generating  ammonia 168 

40.  Distillation  of  nitric  acid 175 

41.  Structure  of  flame i85 

42.  Apparatus  for  making  sulphurous  acid 207 

(xv) 


xvi  LIST  OF  ILLUSTRATIONS. 

FIG-  PAGE 

43.  Apparatus  for  detection  of  phosphorus 223 

44-47.  Detection  of  arsenic 353-357 

48-52.  Apparatus  for  analytical  operations 372,  373 

53.  Heating  of  solids  in  bent  glass  tube 377 

54.  Heating  on  charcoal  by  means  of  blowpipe 377 

55.  Washing  and  decanting  in  agate  mortar 378 

56.  Platinum  wire  for  blowpipe  experiments v  379 

57.  58.  Apparatus  for  generating  hydrogen  sulphide 384 

59.  Drying-oven 403 

60.  Desiccator 404 

61.  Watch-glass  for  weighing  filters 404 

62.  Liter  flask 405 

63.  Pipettes 405 

64.  Mohr's  burette  and  clamp 406 

(}•").  Mohr's  burette  and  holder 406 

66.  Gay  Lussac's  burette 407 

67.  Flask  for  dissolving  iron .  419 

68.  Gas-furnace  for  organic  analysis 444 

69.  Flasks  for  fractional  distillation      463 

70.  Liebig's  condenser,  with  flask 484 

71.  Isomeric  salts  of  tartaric  acid      513 

72.  Absorption-spectra  of  blood  constituents 658 

73.  Uriuometer 707 

74.  Doremus'  ureometer 714 

75.  Esbach's  albuminometer 727 

76.  Various  forms  of  uric  acid  crystals 741 

77.  Calcium  oxalate  crystals 742 

78.  Crystalline  phosphates 742 

79.  Ammonium  urate  crystals     ....... 743 

80.  Crystals  of  leucine ^ 743 

81.  Tyrosine  crystals 744 

82.  Crystals  of  cystine 744 


COLORED  PLATES. 


PLATE  Of  Spectra 

"  I.  Compounds  of  iron,  cobalt,  and  nickel 

II.  Compounds  of  manganese  and  chromium 

III.  Compounds  of  copper,  lead,  and  bismuth 

IV.  Compounds  of  silver  and  mercury 

V.  Compounds  of  arsenic,  antimony,  and  tin 

VI.  Reactions  of  alkaloids    .... 

VII.  Indicators  for  alkalies  and  acids     . 

£t      VIII.  Physiological  reactions   .... 


.  Frontispiece. 

facing  page  302 

"      312 

"     326 

"        "     344 

"        "     352 

"        "     602 

"     680 
«     738 


ABBREVIATIONS. 

c.c.          =  Cubic  centimeter. 

B.  P.      =  Boiling-point. 

F.  P.      =  Fusing-pointc 

Sp.  gr.    =  Specific  gravity. 

U.  S.  P.  =  United  States  Pharmacopeia. 


(xvii) 


PRACTICAL  CHEMISTRY, 
MEDICAL  AND  PHARMACEUTICAL, 


I. 

CHEMICAL  PHYSICS. 

BOTH  sciences,  chemistry  and  physics,  have  for  their  object  the 
study  of  all  substances,  or  of  all  varieties  of  matter,  and  the  changes 
which  they  undergo.  When  these  alterations  affect  the  composition 
of  matter  we  have  chemical  changes,  which  are  considered  by  chem- 
istry ;  when  the  composition  is  not  affected Ve  have  physical  changes, 
considered  by  physics.  But  whenever  chemical  changes  take  place 
they  are  accompanied  by  physical  changes.  Indeed,  there  exists  such 
a  close  relation,  such  a  mutual  dependency,  between  these  two  series 
of  phenomena  that  they  cannot  be  studied  altogether  independently 
of  one  another.  Moreover,  the  chemist  uses  constantly  in  his  opera- 
tions instruments  or  appliances  the  construction  of  which  is  based  on 
physical  principles.  A  knowledge  of  certain  parts  of  physics  is 
therefore  essential  for  the  proper  understanding  of  chemistry.  It  is 
for  this  reason  that  a  few  chapters  dealing  with  certain  physical  con- 
ditions of  matter  precede  the  parts  on  chemistry. 

Physics  is  defined  above  as  the  study  of  those  changes  in  matter  which  do 
not  involve  an  alteration  of  the  composition  or  constitution  of  the  matter. 
The  phenomena  of  light,  heat,  electricity,  magnetism,  sound,  motion,  attrac- 
tion, etc.,  fall  within  its  province.  A  few  examples  of  physical  changes  may 
help  to  make  the  subject  clearer.  A  piece  of  iron  heated  sufficiently  becomes 
luminous,  radiates  heat,  and  increases  in  size.  All  these  are  physical  changes, 
because  if  the  iron  be  cooled  it  will  be  found  to  be  the  same  in  character  as 
before  it  was  heated.  There  has  been  no  change  in  the  substance  iron.  A 
body  in  rapid  motion  is  quite  different  from  the  same  body  at  rest,  as  is  evident 
if  the  body  hit  an  individual,  yet  the  nature  or  composition  of  the  body  is  not 
altered.  A  wire  through  which  an  electric  current  is  passing  is  different  from 
2  17 


18  CHEMICAL  PHYSICS. 

one  in  which  there  is  no  current,  although  the  substance  of  both  wires  is  the 
same.     Many  other  examples  of  physical  change  might  be  cited. 

Chemistry  is  the  study  of  those  changes  in  bodies  which  affect  their  compo- 
sition, and  in  this  respect  chemical  changes  differ  from  all  other  kinds  of 
changes.  Another  good  and  broad  definition  given  by  the  great  Russian  chem- 
ist, Mendelejeff,  is  the  following:  Chemistry  is  concerned  with  the  study  of  the 
homogeneous  substances  or  materials  of  which  all  objects  of  the  universe  are 
made  up,  with  the  transformations  of  these  substances  into  one  another,  and 
with  the  phenomena  which  accompany  such  transformations.  When  a  piece 
of  paper  burns,  an  ash  is  left,  which  is  altogether  different  from  the  original 
paper.  Moreover,  if  proper  care  be  taken  to  catch  the  products  escaping  dur- 
ing the  burning,  water  vapor  and  gases  will  be  found,  which  are  also  unlike 
the  paper.  These  are  new  substances  and  the  change  is,  therefore,  a  chemical 
one.  But  at  the  same  time  several  physical  changes  will  be  observed,  namely, 
heat  and  light. 

When  a  piece  of  the  metal  magnesium  is  ignited,  it  burns  and  leaves  an  ash 
entirely  different  from  the  metal,  being  white  and  brittle.  This  is  a  chemical 
change,  but  heat  and  intense  light  are  observed  at  the  same  time,  which  are 
physical  changes. 

When  a  piece  of  marble  is  heated  to  redness  for  some  time,  a  substance 
remains  on  cooling  which,  although  having  the  same  form  as  the  piece  o> 
marble,  is  nevertheless  entirely  different  in  its  composition  and  properties,  anr* 
is  known  as  quick-lime.  When  water  is  poured  upon  the  latter,  great  heat  is 
produced  .and  the  solid  lump  falls  down  to  a  white  powder,  known  as  slaked- 
lime,  whereas  marble  is  not  affected  by  water.  By  a  suitably  arranged  appa- 
ratus it  could  also  be  shown  tfiat  an  invisible  gas  is  given  off  when  the  marble 
is  heated. 

These  illustrations  will  be  sufficient  to  point  out  the  nature  of  physical  and 
chemical  changes,  and  we  may  proceed  now  to  the  discussion  of  some  element- 
ary subjects  of  physics. 

1.  FUNDAMENTAL   PROPERTIES   OF  MATTER. 

Matter  is  anything  that  occupies  space  and  may  be  apprehended 
by  the  aid  of  our  senses.  While  there  are  many  thousands  of  various 
kinds  of  matter,  possessing  widely  different  properties,  yet  there  are 
properties  in  common  which  belong  to  'every  kind  of  matter,  and 
these  are  known  as  essential  or  fundamental  properties.  The  funda- 
mental properties  of  matter  having  a  special  interest  for  those  study- 
ing chemistry  are :  Extension,  Divisibility,  Gravitation,  Porosity,  and 
Indestructibility. 

Extension.  The  common  property  of  matter  to  occupy  space  is 
known  as  extension.  All  bodies,  without  exception,  fill  a  certain 
quantity  of  space ;  they  all  have  length,  breadth,  and  thickness. 
That  portion  of  matter  lying  within  the  surrounding  surface  of  a 
body  is  called  its  mass;  or  we  may  define  mass  as  the  quantity  of 


FUNDAMENTAL  PROPERTIES  OF  MATTER.  19 

matter  which  a  body  possesses.  A  body  is  a  definite  portion  of 
matter,  such  as  a  knife,  a  piece  of  chalk,  or  a  lump  of  coal.  The 
term  substance  is  used  to  designate  some  particular  kind  of  matter, 
possessed  of  definite  qualities,  such  as  gold,  water,  glass,  etc.  We 
distinguish  three  different  conditions  of  matter,  namely :  Solids, 
Liquids,  and  Gases.1  These  conditions  of  matter  are  known  as  the 
three  states  of  aggregation,  and  we  will  now  consider  the  peculiarities 
of  matter  when  existing  in  either  of  these  states. 

Solid  state.  Solids  are  distinguished  by  a  self-subsistent  figure — 
i.  e.,  they  have  a  definite  size  and  shape.  A  solid  substance  forms 
for  itself,  as  it  were,  a  casing  in  which  its  smallest  particles1  are  en- 
closed. The  questions  arise,  By  what  means  are  these  particles  con- 
nected? How  are  they  kept  together?  No  answer  can  be  given 
other  than  that  the  particles  themselves  attract  each  other  to  such  an 
extent  that  force  is  necessary  to  make  them  alter  their  relative  posi- 
tions. We  see,  consequently,  that  some  form  of  attraction  or  at- 
tractive power  is  acting  between  the  particles  of  a  solid  mass,  and 
we  call  this  kind  of  attraction  cohesion,  to  distinguish  it  from  other 
forms  of  attraction. 

Force  may  be  defined  as  the  action  of  one  body  upon  another 
body,  or  as  the  action  of  particles  of  matter  upon  other  particles 
either  of  the  same  or  of  another  body.  Strictly  speaking,  we  may 
say  that  force  is  the  cause  tending  to  produce,  change,  or  arrest 
motion  ;  or  it  is  any  action  upon  matter  changing  or  tending  to  change 
its  form  or  position.  Force  is  a  manifestation  of  energy,  and  may 
be  originated  in  a  variety  of  ways. 

Energy  is  a  universal  property  of  matter ;  it  is  its  capacity  for 
doing  work,  and  is  measured  by  the  work  it  can  do.  Doing  work  con- 
sists in  a  transfer  of  motion,  or  energy,  from  the  body  doing  work  to 
the  body  on  which  work  is  done.  Wherever  we  find  matter  in  motion 
we  have  a  certain  quantity  of  energy  which  may  be  made  to  do  work. 

As  examples  of  different  forms  of  energy  we  have  motion  of  masses,  heat, 
light,  electricity,  chemical  changes,  etc.  Under  the  influence  of  the  different 
forms  of  energy  matter  is  constantly  undergoing  change.  There  are  changes 
in  position,  in  temperature,  in  appearance,  in  the  composition  of  substances, 
and  in  many  other  directions. 

1  It  has  been  shown  lately  that  matter  may  exist  in  a  fourth  state  as  radiant  matter.    This 
condition  will  be  considered  later. 

2  It  will  be  shown  later  that  all  matter  is  supposed  to  consist  of  smallest  particles,  which  we 
call  molecules. 


20  CHEMICAL  PHYSICS. 

Energy  may  be  potential  (i.  e.,  stored  up)  or  kinetic  (i.  e.,  actual).  For 
instance,  potential  energy  is  the  energy  which  we  have  in  a  mass  held  by 
the  hand,  or  by  a  support ;  as  soon  as  the  support  is  withdrawn  the  mass  falls, 
and  in  this  instance  we  witness  kinetic  or  actual  energy. 

Other  instances  of  potential  energy  are  a  drawn  bow,  a  wound-up  watch- 
spring,  an  elevated  tank  of  water,  etc.  This  potential  energy  may  manifest 
itself  as  kinetic  energy  by  sending  an  arrow  through  space,  by  keeping  the 
watch  in  motion,  or  by  rotating  a  water-wheel.  During  the  conversion  of 
potential  into  kinetic  energy  there  is  neither  gain  nor  loss  ;  both  are  absolutely 
alike  in  quantity. 

Crystallization.  The  external  appearance  or  the  figure  of  solid 
bodies  is  various.  It  may  be  an  irregular  or  a  natural  regular  figure. 
Of  these  two  forms,  only  the  latter  is  here  of  interest,  as  it  includes 
all  the  different  crystallized  substances. 

Crystals  are  solid  substances  bounded  by  plane  surfaces  symmetri- 
cally arranged  according  to  fixed  laws.  In  explaining  the  formation 
of  crystals  we  have  to  assume  that  the  particles  are  endowed  with  the 
power  of  attracting  one  another  in  certain  directions,  thereby  building 
themselves  up  into  geometrical  forms. 

The  external  form  of  a  crystal  is  only  an  outward  expression  of  a  regular 
internal  structure.  This  is  shown  by  the  fact  that  in  non-crystalline  homo- 
geneous bodies  such  properties  as  elasticity,  hardness,  cohesion,  transmission 
of  light,  etc.,  are  the  same  in  all  directions,  while  crystallized  bodies  show  dif- 
ferences along  different  directions.  A  model  of  glass  would  not  be  a  crystal, 
since  the  necessary  internal  structure  is  absent. 

The  first  condition  essential  to  the  formation  of  crystals  is  the  possi- 
bility of  free  motion  of  the  smallest  particles  of  the  matter  to  be  crys- 
tallized ;  in  that  case  only  will  they  be  able  to  attract  each  other  in 
such  a  way  as  to  assume  a  regular  shape,  or  form  crystals.  Particles 
of  a  solid  mass  can  move  freely  only  after  they  have  been  transferred 
to  the  liquid  or  gaseous  state.  There  are  two  different  methods  of 
liquefaction,  viz.,  by  means  of  heat  (melting),  or  solution  in  some 
suitable  agent  (dissolving).  In  the  liquid  condition  thus  produced, 
the  smallest  particles  can  follow  their  own  attraction,  and  unite  to 
form  crystals  on  removal  of  the  cause  of  liquefaction  (heat  or  solvent). 

In  the  great  majority  of  cases  the  method  employed  for  obtaining  crystals 
is  to  dissolve  the  substance  in  a  liquid,  usually  water,  taking  advantage  of  the 
fact  that,  with  very  few  exceptions,  substances  are  more  soluble  in  hot  than  in 
cold  liquids.  When  such  a  concentrated  hot  solution,  filtered  if  necessary  to 
remove  solid  matter,  is  allowed  to  cool,  the  particles  of  the  excess  of  the  sub- 
stance, beyond  what  is  soluble  at  the  lower  temperature,  gradually  arrange 


FUNDAMENTAL  PROPERTIES  OF  MATTER.  21 

themselves  around  certain  points  as  nuclei  according  to  the  directions  of  great- 
est cohesion,  and  thus  crystals  with  regular  faces  and  angles  and  definite 
internal  arrangement  are  built  up.  The  size  of  the  crystals  obtained  will 
depend  on  several  factors,  but  whatever  the  size  may  be,  the  angles  between 
the  faces  and  the  position  of  the  faces  will  be  the  same  for  every  individual 
substance.  Hence  the  shape  of  crystals  is  a  valuable  means  of  identifying 
substances.  If  a  concentrated  hot  solution  of  a  substance  be  cooled  quickly, 
and  especially  if  the  liquid  be  disturbed,  as  by  stirring,  the  crystals  will  be 
small,  sometimes  almost  microscopic  in  size.  But  this  is  often  an  advantage, 
because  large  crystals  are  apt  to  enclose  some  of  the  liquid  containing  the 
impurities  between  the  layers.  On  the  large  scale,  as  in  industries,  enormous 
crystals  are  obtained  by  the  slow  cooling  of  a  great  volume  of  solution,  for 
example,  in  the  case  of  alum,  potassium  dichromate,  etc.  When  a  substance 
is  not  much  more  soluble  in  a  hot  than  in  a  cold  liquid,  for  example,  common 
salt  in  water,  the  liquid  must  be  removed  by  allowing  it  to  evaporate,  either  at 
ordinary  or  at  elevated  temperature,  to  obtain  a  good  yield  of  the  substance 
in  crystal  form. 

Sometimes  sticks,  strings,  wires,  strips  of  lead,  etc.,  are  suspended  in  the 
solutions,  to  offer  starting-points  for  the  formation  of  crystals  and  a  ready 
means  for  removing  the  crystals  from  the  liquor.  A  familiar  example  is  the 
string  in  the  center  of  a  stick  of  rock-candy. 

A  relatively  few  substances  when  heated  pass  from  the  solid  to  the  gaseous 
state,  without  undergoing  intermediate  liquefaction.  When  the  vapor  of  such 
substances  comes  in  contact  with  cool  surfaces,  it  is  deposited  in  crystals  which 
sometimes  attain  to  remarkable  size  and  beauty.  This  process  is  known  as 
sublimation  and  is  used  in  the  case  of  several  medicinal  agents  on  the  market, 
for  example,  iodine,  benzoic  acid,  ammonium  chloride,  etc.  The  words  iodine 
resublimed,  found  on  labels,  and  the  popular  name  for  mercuric  chloride,  namely, 
corrosive  sublimate,  refer  to  the  process  of  sublimation  employed  in  obtaining 
these  substances. 

If  two  or  more  (non-isomorphous)  substances — for  instance,  common  salt 
and  Glauber's  salt— be  dissolved  together  in  water,  and  the  solution  be  allowed 
to  crystallize,  the  attraction  of  like  particles  for  one  another  will  be  readily 
noticed  by  the  formation  of  distinct  crystals  of  common  salt  alongside  of 
crystals  of  Glauber's  salt ;  neither  do  the  particles  of  common  salt  help  to 
build  up  a  crystal  of  Glauber's  salt,  nor  the  particles  of  the  latter  a  crystal  of 
common  salt.  Advantage  is  taken  of  this  property  in  separating  (by  crystal- 
lization) solids  from  each  other,  when  they  are  contained  in  the  same  solution. 

Not  all  matter  can  form  crystals ;  some  substances  never  have  been 
obtained  in  a  crystallized  state,  such  as  starch,  gum,  glue,  etc.  A 
solid  substance  showing  no  crystalline  structure  whatever  is  called 
amorphous. 

Some  substances  capable  of  crystallization  may  be  obtained  also  in 
an  amorphous  state  (carbon,  sulphur).  Other  substances  are  capable 
of  assuming  different  crystalline  shapes  under  different  conditions. 
Thus  sulphur,  when  liquefied  by  heat,  assumes,  on  cooling,  a  shape 
different  from  the  sulphur  crystallized  from  a  solution.  One  and  the 


22 


CHEMICAL  PHYSICS. 


same  substance  under  the  same  conditions  always  assumes  the  same 
shape.  Substances  capable  of  assuming  in  solidifying  two  or  more 
different  shapes  or  conditions,  are  said  to  be  dimorphous  and  poly- 
morphous, respectively.  When  substances  of  different  kinds  crystallize 
in  exactly  the  same  form  we  call  them  isomorphous  (magnesium  sul- 
phate and  zinc  sulphate).  Also,  a  crystal  of  one  kind  of  matter  must 
have  the  power  of  growing  in  the  solution  of  another  kind  before 
the  two  kinds  of  matter  are  considered  isomorphous.  If  two  iso- 
morphous substances  be  contained  in  one  solution,  they  will  crystallize 
together,  and  the  crystals  be  made  up  of  particles  of  both  substances, 

Crystal  Systems.  The  study  of  crystals  forms  an  extensive  field,  known 
as  crystallography.  The  limited  scope  of  this  book  forbids  any  detailed  study 
of  crystals,  and  the  reader  must  be  referred  to  the  large  works  on  chemistry  or 
works  on  crystallography  for  such  information.  But  a  brief  description  of  the 
classification  of  crystals  may  not  be  out  of  place  here. 

All  crystals  are  referred  to  axes  or  imaginary  lines  drawn  through  the  cen- 
ter. The  great  variety  of  forms  of  crystals  depends  upon  the  number  and 
length  of  these  axes  and  their  relative  inclination — that  is,  the  angles  at  which 
they  intersect.  All  crystal  forms  have  been  divided  into  two  large  groups,  the 
orthometric  and  the  clinometric,  and  these  have  been  further  subdivided  into  six 
systems.  Orthometric  refers  to  the  fact  that  the  axes  intersect  at  right  angles, 
while  clinometric  means  that  the  axes  intersect  at  oblique  angles. 


FIG.  1. 


FIG.  2. 


The  cube.  Regular  octahedron. 

The  orthometric  group  includes  the  following  systems  : 

(1)  Kegular   system,   also  known  as  the  monometric,   cubic,  octahedral,  or 
tessular  system. 

The  crystals  have  three  axes  of  equal  length  and  intersecting  at  right  angles. 
The  fundamental  forms  of  this  system  are  the  cube  and  the  octahedron  (Figs. 
1  and  2).  Some  substances  crystallizing  in  this  system  are  alum,  phosphorus, 
arsenic  trioxide,  diamonds,  alkali  iodides,  chlorides,  fluorides,  and  cyanides, 
and  many  metals  and  their  sulphides. 

(2)  Quadratic  system,  also  known  as  the  dimetric,  square  prismatic,  or  tet- 
ragonal system. 


FUNDAMENTAL  PROPERTIES  OF  MATTER. 


The  crystals  have  three  axes  intersecting  at  right  angles,  two  of  which  are 
of  equal  length  and  one  either  longer  or  shorter  than  the  other  two.  The  fun- 
damental forms  of  this  system  are  the  quadratic  octahedron  (also  known  as 
square-based  double  pyramid)  and  the  right  square  prism  (Figs.  3  and  4). 

FIG.  3.  FIG.  4. 


Quadratic  octahedron.  Right-square  or  quadratic  prism. 

Some  substances  crystallizing  in  this  system  are  potassium  ferrocyanide,  calo- 
mel, nickel  sulphate,  tin,  tin  oxide,  magnesium  sulphate,  zinc  sulphate. 

(3)  Rhombic  system,  also  known  as  the  trimetric  or  right  prismatic  system. 

FIG.  5.  FIG.  6. 


Rhombic  octahedron.  Double  six-sided  pyramid. 

The  crystals  have  three  unequal  axes  intersecting  at  right  angles.  The  fun- 
damental form  of  this  system  is  the  rhombic  octahedron  or  right  rhombic 
double  pyramid  (Fig.  5).  Some  substances  crystallizing  in  this  system  are 


24 


CHEMICAL  PHYSICS. 


potassium  sulphate  and  nitrate,  resorcin,  zinc  sulphate,  citric  acid,  iodine, 
Rochelle  salt,  mercuric  chloride,  barium  chloride,  tartar  emetic,  codeine,  sali- 
cylic acid,  piperin,  Epsom  salt,  silver  nitrate,  ammonium  sulphate,  cream  of 
tartar. 

(4)  Hexagonal  or  rhombohedral  system. 

The  crystals  have  four  axes,  three  of  which  are  of  equal  length,  while  the 
fourth  is  either  longer  or  shorter  than  the  other  three.  The  three  equal  axes 
are  in  the  same  plane  and  intersect  at  an  angle  of  60°,  while  the  fourth  axis 
intersects  these  at  right  angles.  The  fundamental  form  is  the  double  six-sided 
pyramid.  The  rhombohedron  and  regular  six-sided  prism  are  modifications 
of  this  system  (Figs.  6,  7,  and  8).  Some  substances  crystallizing  in  this  system 


FIG.  7. 


FIG.  8. 


i  —  i  •  —  i 

i 

j 
j 

L  

<L.., 

Rhombohedron. 


Six-sided  prism. 


are  sodium  nitrate,  camphor,  graphite,  ammonium  chloride,  ice,  calcspar,  thy- 
mol, metallic  bismuth  and  antimony,  arsenic,  silicic  acid. 

The  clinometric  group  includes  the  following  systems : 

(5)  Monociinic  system,  also  known  as  the  monosymmetric,  clinorhombic,  or 
oblique  prismatic  system. 

The  crystals  have  three  unequal  axes,  two  intersecting  at  oblique  angles  and 
both  intersecting  the  third  at  right  angles.  The  fundamental  forms  of  this 
system  are  the  monoclinic  double  pyramid  or  octahedron  and  the  monoclinic 
prism  (Figs.  9  and  10).  Some  substances  crystallizing  in  this  system  are 

FIG.  9.  FIG.  10. 


Monoclinic  double  pyramid.  Monoclinic  prism. 

ferrous  sulphate,  borax,  lead  acetate,  cupric  acetate,  tartaric  acid,  potassium 
chlorate,  and  sodium  acetate,  sulphate,  thiosulphate,  phosphate,  and  carbonate. 
(6)  Triclinic  system,  also  known  as  the  asymmetric,  clinorhombohedral,  or 
doubly  oblique  prismatic  system. 


FUNDAMENTAL  PROPERTIES  OF  MATTER.  25 

The  crystals  are  the  most  unregular  of  all,  having  three  unequal  axes,  all 
intersecting  at  oblique  angles.  The  fundamental  forms  of  this  system  are  the 
triclinic  prism  and  the  triclinic  octahedron  or  double  pyramid  (Figs.  11  and 
12).  Some  substances  crystallizing  in  this  system  are  copper  sulphate,  potas- 
sium dichromate,  gypsum,  boric  acid,  manganous  sulphate. 

The  pyramidal  form  is  found  in  all  the  systems,  while  the  cube  is  confined 
to  the  regular  system,  and  prisms  occur  in  all  but  the  regular  system. 

FIG.  11.  FIG.  12. 


Triclinic  prism.  Triclinic  octahedron. 

For  some  reason  or  other  crystals  sometimes  grow  mainly  in  one  or  two 
directions  and  then  show  forms  that  are  distorted  and  have  little  or  no  resem- 
blance to  the  normal  forms  of  the  system  to  which  they  belong.  Examples  of 
such  forms  are  the  following : 

Tabular  crystals  or  flat  plates,  as  potassium  chlorate,  iodine,  etc. 

Laminar  crystals,  thin  plates  or  leaflets,  as  acetanilid,  naphthol,  calcium 
hypophosphite,  etc. 

Acicular  crystals  or  needles,  as  aloin,  cinchonidine  sulphate,  quinine 
salts,  etc. 

Prismatic  crystals  or  prisms,  extended  chiefly  in  the  direction  of  the  longest 
axis,  as  salicylic  acid,  santonin,  cinchonine  sulphate,  etc. 

The  shapes  of  gems  must  not  be  confused  with  crystal  forms.  They  are  the 
result  of  cutting  and  polishing  for  the  purpose  of  causing  the  gem  to  reflect 
more  light. 

Characteristic  properties  of  solids.  Solid  substances  show  a 
great  variety  of  properties  caused  by  the  differences  in  the  cohesion 
of  the  particles  (molecules)  composing  the  substances,  and  accordingly 
we  distinguish  between  hard  and  soft,  brittle,  tenacious,  malleable, 
and  ductile  substances. 

Hardness  is  that  property  in  virtue  of  which  some  bodies  resist  attempts  to 
force  passage  between  their  particles,  or  which  enables  solids  to  resist  the  dis- 
placement of  their  particles.  Diamond  and  quartz  are  extremely  hard,  while 
wax  and  lead  are  comparatively  soft. 


26  CHEMICAL  PHYSICS. 

Brittleness  is  that  property  of  solids  which  causes  them  to  be  broken  easily 
when  external  force  is  applied  to  them.  Glass,  sulphur,  coal,  etc.,  are  brittle. 

Tenacity  is  that  property  in  virtue  of  which  solids  resist  attempts  to  pull 
their  particles  asunder.  Steel  is  one  of  the  most  tenacious  substances. 

Malleability,  possessed  by  some  solids,  is  the  property  in  virtue  of  which  they 
may  be  hammered  or  rolled  into  sheets.  Gold  is  so  malleable  that  it  may  be 
beaten  into  sheets  so  thin  that  it  would  require  about  300,000  laid  upon  one 
another  to  measure  one  inch. 

Ductility  is  the  property  in  virtue  of  which  some  solids  may  be  drawn  into 
wire  or  thin  sheets — as,  for  instance,  copper,  iron,  and  platinum. 

Liquid  state.  The  characteristic  features  of  liquids  are,  that  they 
have  no  self-subsistent  figure;  that  they  consequently  require  some 
vessel  to  hold  them ;  and  that  they  present  a  horizontal  surface.  While 
in  a  solid  substance  the  smallest  particles  are  held  together  by  cohe- 
sion to  such  an  extent  that  they  cannot  change  their  relative  position 
without  force,  in  a  liquid  this  cohesion  acts  with  much  less  energy 
and  permits  of  a  comparatively  free  motion  of  the  particles;  the 
repellant  and  attractive  forces  nearly  balance  each  other  in  a  liquid. 
That  cohesion  is  not  altogether  suspended  in  a  liquid  is  shown  by  the 
formation  of  drops  or  round  globules,  which,  of  course,  consist  of  a 
large  number  of  smallest  particles.  If  there  were  no  cohesion  at  all 
between  these  particles  of  a  liquid,  drops  could  not  be  formed. 

The  terms  semi-solid  and  semi-liquid  substances  are  used  for  bodies  occupy- 
ing a  position  intermediate  between  true  solids  and  fluids;  butter,  asphalt, 
amorphous  sulphur,  are  instances  of  this  kind. 

Gaseous  state.  Matter  in  the  gaseous  state  has  absolutely  no 
self-subsistent  figure.  Any  quantity  of  gas  in  a  closed  vessel  will 
fill  it  completely ;  the  smallest  particles  show  the  highest  degree  of 
mobility  and  move  freely  in  every  direction.  Cohesion  is  entirely  sus- 
pended in  gases ;  indeed,  there  is  no  attraction  between  the  particles, 
but  they  are  in  rapid  motion  and  tend  to  spread  out  in  all  directions  ; 
hence  must  be  retained  in  a  closed  vessel.  The  motion  of  the  par- 
ticles causes  bombardment  on  the  sides  of  the  vessel,  and  thus  pro- 
duces pressure.  This  characteristic  property,  possessed  by  all  gases, 
is  known  as  elasticity,  or,  better,  as  tension,  and  is  so  unvarying  that 
a  law1  has  been  established  in  relation  to  it.  This  law  is  known 
as  the  Law  of  Boyle,  who  discovered  it  in  1661 ;  sometimes  it  is 
referred  to  as  the  Law  of  Mariotte.  It  may  be  expressed  thus  :  The 
volume  of  a  gas  is  inversely  as  the  pressure  ;  the  density  and  elastic 
force  are  directly  as  the  pressure  and  inversely  as  the  volume. 

1  In  science,  a  law  or  generalization  is  a  brief  statement  which  describes  some  constant  mode 
of  behavior,  or  sums  up  the  constant  features  of  a  set  of  phenomena  of  a  like  kind. 


FUNDAMENTAL  PROPERTIES  OF  MATTER  27 

The  subject  will  be  clearer  from  the  following  considerations  :  A 
gas  behaves  much  like  a  spring.  If  we  put  weights  (force)  on  the 
spring  it  will  be  compressed — that  is,  its  volume  will  become  less,  and 
if  the  weights  be  gradually  removed,  the  spring  will  expand.  Sim- 
ilarly, if  we  take  a  metallic  tube  closed  at  one  end,  and  fitted  with  a 
piston  and  handle  and  containing  a  certain  volume  of  air,  for 
example,  a  bicycle  pump,  and  then  press  down  upon  the  handle,  the 
volume  of  air  will  become  smaller  and  smaller  as  the  pressure  on  the 
handle  is  increased.  It  will  be  observed  also  that  as  the  volume 
becomes  smaller  it  oifers  more  and  more  resistance  to  compression, 
that  is,  its  tension  or  elastic  force  becomes  greater.  Also,  since  the 
amount  of  material  in  the  original  volume  of  air  remains  the  same 
during  the  experiment,  it  is  plain  that  when  the  air  is  compressed  to 
a  small  volume,  the  amount  of  material  in  a  unit  volume,  say  1  cubic 
inch,  is  very  much  increased  ;  in  other  words,  the  density  of  the  gas  is 
increased  as  the  pressure  is  increased.  If  accurate  measurements  be 
made  of  the  different  pressures  applied  and  the  corresponding  vol- 
umes assumed  by  the  air,  a  constant  relationship  will  be  discovered, 
such  as  is  expressed  in  Boyle's  Law,  stated  above.  The  meaning  of 
the  phrase  in  the  law,  the  volume  of  a  gas  is  inversely  as  the  pressure, 
is  that  as  the  one  quantity  is  increased  the  other  is  decreased  in  just 
the  same  proportion.  To  illustrate,  if  a  volume  of  a  gas  measure  1 
cubic  foot  under  a  pressure  of  10  pounds,  and  the  pressure  be 
increased  to  15  pounds,  in  other  words,  ||  or  f  times,  then  the  vol- 
ume will  change  from  1  cubic  foot  to  1  -s-  f  =  f  cubic  foot.  If  the 
pressure  be  decreased  to  say  6  pounds,  or  -f^  —-  f  of  its  original  value, 
then  the  volume  will  become  1  -*-  f  =  f  cubic  foot,  that  is,  it  will 
expand. 

Such  a  relation  as  is  expressed  in  Boyle's  Law  is  known  in  algebra 
as  inverse  proportion.  Since  one  of  the  quantities  is  always  decreased 
in  the  same  ratio  as  the  other  is  increased,  it  follows  that  the  product 
of  the  two  quantities  thus  related  must  always  be  the  same,  that  is,  a 
constant.  Hence,  another  way  of  expressing  Boyle's  Law  is  to  say 
that  the  product  of  the  pressure  and  the  corresponding  volume  of  a 
definite  quantity  of  a  gas  is  always  the  same.  If  V  and  V1  repre- 
sent the  volumes  of  a  certain  amount  of  gas,  at  the  corresponding 
pressures,  P  and  F,  then  V  X  P  =  V1  X  P.  In  the  example 
given  above,  Y  ==  1  cubic  foot,  P  =  10  pounds,  and  P1  =  15  pounds, 
hence,  1  X  10  =  V1  X  15,  or  V1  ==  |g-  =  f  cubic  foot. 

As  will  be  seen  later,  this  law  is  of  great  value  in  all  experiments 
where  results  are  calculated  from  measurements  of  gas  volumes. 


28  CHEMICAL  PHYSICS. 

Vapors  from  liquids  and  solids  at  sufficient  temperatures  above  their 
points  of  condensation  behave  just  like  gases. 

Divisibility.  All  matter  admits  of  being  subdivided  into  smaller 
particles,  and  this  property  is  called  divisibility.  The  processes  by 
which  we  accomplish  the  comminution  of  a  solid  substance  may 
be  of  a  mechanical  nature,  such  as  cutting,  crushing,  grinding ;  but 
beside  these  modes  of  subdivision  we  have  other  agents  or  causes 
by  which  matter  may  be  divided  into  smaller  particles,  and  one  of 
these  agents  is  heat. 

Action  of  heat  on  matter.  Let  us  take  a  piece  of  ice  and 
convert  it,  by  means  of  mortar  and  pestle,  into  a  very  fine  powder. 
When  the  smallest  particle  of  this  finely  powdered  ice  is  placed 
under  the  microscope  and  heat  applied,  we  shall  observe  that  it 
becomes  liquid,  thus  proving  that  it  was  capable  of  further  sub- 
division, that  it  consisted  of  smaller  particles,  which  have  now  by 
the  action  of  heat  become  movable.  By  further  applying  heat  to  the 
liquid  particle  of  water  we  may  convert  it  into  a  gas  or  vapor,  which 
will  escape  into  the  air,  or  which  we  may  collect  in  an  empty  flask. 
The  flask  will  be  filled  completely  by  this  water-gas  (or  steam) 
obtained  by  vaporizing  that  minute  particle  of  ice-dust.  This  fact 
demonstrates  that  mechanical  comminution  does  not  carry  us  beyond 
a  certain  degree  of  subdivision  of  matter.  That  is  to  say,  the  smallest 
fragment  of  the  finest  powder  still  consists  of  a  very  large  number  of 
much  smaller  particles.  To  the  smallest  particles  which  compose 
matter  the  name  molecules  has  been  given. 

Molecular  theory.  The  expression  molecule  is  derived  from  the 
Latin  word  molecula — a  little  mass,  and  means  the  smallest  particle 
of  matter  that  can  exist  by  itself,  or  into  which  matter  is  capable  of 
being  subdivided  by  physical  actions.  To  explain  more  fully  what  is 
meant  by  the  expression  molecule,  we  will  return  to  the  conversion  of 
water  into  steam. 

When  water  boils  at  the  ordinary  atmospheric  pressure  it  expands 
about  1800  times,  or  one  cubic  inch  of  water  yields  about  1800  cubic 
inches,  equal  to  about  one  cubic  foot  of  steam.  In  explaining  this 
fact  we  have  either  to  assume  that  the  water,  as  well  as  the  steam,  is 
continuous  matter  (Fig.  13),  or  that  the  water  consisted  of  small  par- 
ticles of  a  given  size,  which  now  exist  in  the  steam  again  as  such, 


FUNDAMENTAL  PROPERTIES   OF  MATTER.  29 

FIG.  13. 


with  the  only  difference  that  they  are  more  widely  separated  from 
each  other  (Fig.  14). 

FIG.  14. 


Of  the  many  proofs  which  we  have  of  the  fact  that  the  latter 
assumption  is  correct,  one  may  be  sufficient,  viz.,  that  the  quantities 
of  vapor  formed  by  volatile  liquids  at  any  certain  temperature  above 
the  boiling-point,  in  close  vessels  of  the  same  size,  are  the  same,  no 
matter  whether  the  vessel  was  entirely  empty  or  contains  the  vapors 
of  one,  two,  or  more  other  substances.  For  instance  :  If  we  place 
one  cubic  inch  of  water  in  a  flask  holding  one  cubic  foot,  from  which 
flask  the  air  has  been  previously  removed,  and  then  heat  the  flask  to 
the  boiling-point,  the  cubic  inch  of  water  will  evaporate,  filling  the 
vessel  with  steam.  Upon  now  introducing  into  the  flask  a  second  and 


30  CHEMICAL  PHYSICS. 

a  third  liquid — for  instance,  alcohol  and  ether — we  find  that  of  each 
of  these  liquids  exactly  the  same  quantity  will  evaporate  which  would 
have  evaporated  if  these  liquids  had  been  introduced  into  the  empty 
flask.1  This  fact  is  evidence  that  there  must  be  small  particles  of 
steam  which  are  not  in  close  contact,  that  there  are  spaces  between 
these  particles  which  may  be  occupied  by  the  particles  of  a  second, 
third,  or  more  substances.  To  these  particles  of  matter  we  give  the 
name  molecules,  and  the  spaces  between  them  we  call  intermolecular 


We  have  thus  demonstrated  the  correctness,  or,  at  least,  the  likeli- 
hood, of  the  so-called  molecular  theory,  but  the  proof  given  is  but  one 
of  many.  Other  facts  which  lead  us  to  accept  the  theory  of  the 
molecular  condition  cf  matter  are  :  The  passage  of  gases  through 
solids  :  for  example,  of  carbon  dioxide  gas  through  red-hot  iron  ;  of 
water  under  pressure  through  gold  ;  the  decrease  in  a  volume  of  water 
when  a  salt  is  dissolved  in  it ;  the  extreme  divisibility  of  matter  as 
shown  by  solution,  etc. 

Our  conception  of  molecules  (though  individually  by  far  too  small  to  make 
any  impression  whatever  upon  our  senses)  is  so  perfect  that  we  have  formed  an 
idea  of  the  actual  size  of  these  minute  particles  of  matter.  Very  good  reasons 
lead  us  to  believe  that  the  diameter  of  a  molecule  is  equal  to  about  CTnn&rnnnj 
of  one  inch,  and  that  one  cubic  inch  of  a  gas  under  ordinary  conditions  con- 
tains about  one  hundred  thousand  million  million  milions  of  molecules. 

These  figures  at  first  glance  appear  to  be  beyond  the  limit  of  human  con- 
ception, but  in  order  to  give  some  idea  of  the  size  of  these  molecules  it  may  be 
mentioned  that  if  a  mass  of  water  as  large  as  a  pea  were  to  be  magnified  to  the 
size  of  our  earth,  each  molecule  being  magnified  in  the  same  proportion,  these 
molecules  would  represent  balls  of  about  two  inches  in  diameter. 

While  molecules  consequently  are  exceedingly  small  particles,  yet  they  are 
not  entirely  immeasurable ;  they  are,  as  Sir  W.  Thomson  says,  pieces  of  matter 
of  measurable  dimensions,  with  shape,  motion,  and  laws  of  action,  intelligible 
subjects  of  scientific  investigation. 

Intimately  connected  with  the  molecular  theory  is  the  Law  (more 
correctly,  the  hypothesis)  of  Avogadro,  which  may  be  stated  as  follows  : 
All  gases  or  vapors,  without  exception,  contain,  in  the  same  volume,  the 
same  number  of  molecules,  provided  temperature  and  pressure  are  the 
same.  Or,  in  other  words  :  Equal  volumes  of  different  gases  contain, 
under  equal  circumstances,  the  same  number  of  molecules.  The  correct- 
ness of  this  law  has  good  mathematical  support  deduced  from  the  law 
of  Boyle,  many  other  facts  and  considerations  leading  to  the  same 

1  As  each  gas,  in  consequence  of  its  tension,  exerts  a  certain  pressure,  the  pressure  in  the 
flask  rises  with  the  introduction  of  every  additional  gas. 


FUNDAMENTAL   PROPERTIES  OF  MATTER.  31 

assumption.     We  shall  learn,  hereafter,  that  the  law  of  Avogadro  is 
one  of  the  greatest  importance  to  the  science  of  chemistry. 

Gravitation.  Every  particle  of  matter  in  the  universe  attracts 
every  other  particle ;  consequently,  all  masses  attract  each  other,  and 
this  attraction  is  known  as  gravitation.  The  action  of  gravitation 
between  the  thousands  of  heavenly  bodies  moving  in  the  universe  is 
to  be  considered  by  astronomy,  but  some  of  the  phenomena  caused 
by  the  mutual  attraction  of  the  substances  composing  the  earth  are 
of  importance  for  our  present  consideration. 

Such  phenomena  caused  by  gravitation  are  the  falling  of  substances, 
the  flowing  of  rivers,  the  resistance  which  a  substance  offers  on  being 
lifted  or  carried.  A  body  thrown  up  into  the  air  or  deprived  of  its 
support  will  fall  back  upon  the  earth.  In  this  case  the  mutual  attrac- 
tion between  the  earth  and  the  substance  has  caused  its  fall.  It 
might  appear  that  in  this  case  the  attraction  was  not  mutual,  but  ex- 
erted by  the  earth  only;  it  has  been  proved,  however,  by  most  exact 
experiments,  that  there  is  also  an  attraction  of  the  falling  substance 
for  the  earth,  but  the  amount  of  the  force  of  this  attraction  is  directly 
proportional  to  th.e  mass  of  the  bodies,  and  consequently  too  insig- 
nificant in  the  above  case  to  be  noticed. 

The  law  of  gravitation,  known  as  Newton's  law,  may  thus  be  stated : 
All  bodies  attract  each  other  with  a  force  directly  proportional  to 
their  masses  and  inversely  proportional  to  the  squares  of  their  distance 
apart.  With  regard  to  the  earth  and  bodies  upon  it  at  a  given  place, 
the  mass  of  the  earth  and  the  distance  between  the  earth  and  the 
bodies  remain  the  same,  so  that  the  only  thing  that  varies  is  the  mass 
of  the  bodies.  Hence,  according  to  Newton's  Law,  the  force  with 
which  such  bodies  are  attracted  to  the  earth  varies  directly  as  their 
masses.  In  other  words,  if  a  body  A  has  twice  the  mass  or  quan- 
tity of  matter  as  a  body  B,  it  will  be  attracted  with  twice  as  much 
force  to  the  earth  as  the  body  B. 

Weight  is  an  expression  used  to  denote  the  quantity  of  mutual 
attraction  between  the  earth  and  the  body  weighed.  When  we  weigh 
bodies  on  a  balance,  we  primarily  compare  two  forces,  namely,  the 
pull  of  the  earth  on  each  of  the  bodies  on  the  pans  of  the  balance, 
nevertheless,  we  can  use  the  balance  to  measure  mass  or  quantity  of 
matter.  For  if  two  bodies  are  exactly  balanced,  that  is,  "  weigh  " 
the  same,  we  know  that  the  pull  of  the  earth  is  the  same  on  each,  and 
since  this  attraction,  as  was  shown  above,  is  directly  proportional  to 


32  CHEMICAL  PHYSICS. 

the  masses  or  quantity  of  matter  in  the  two  bodies,  the  masses  must 
be  equal.  That  weight  and  mass  are  different  ideas  is  evident  from 
the  fact  that  the  force  with  which  a  given  body  is  attracted  by  the 
earth  varies  according  to  latitude  and  elevation  above  the  earth,  while 
the  quantity  of  matter  remains  the  same.  But  if  two  bodies  weigh 
the  same  in  one  place,  they  will  do  so  in  any  other  place.  All  our 
weighing  is  a  comparison  with,  or  measurement  by,  some  standard 
weight,  such  as  pound,  ounce,  gramme,  etc. 

For  scientific  purposes  the  weight  of  bodies  is  sometimes  deter- 
mined invacuo,  because  it  eliminates  an  error  due  to  the  buoyant  effect 
of  atmospheric  air.  Weight  thus  determined  is  called  absolute  weighty 
while  by  ordinary  methods  we  obtain  apparent  weight. 

"Weights  and  measures.  For  scientific  purposes  the  metric  or  decimal 
system  of  weights  and  measures  is  used  the  world  over.  This  system  is  used  also 
for  general  purposes  by  practically  all  except  the  English-speaking  nations. 
While  metric  weights  and  measures  were  legalized  in  the  United  States  and 
Great  Britain  in  1866,  unfortunately  neither  country  has  as  yet  enforced  their 
general  adoption.  The  U.  S.  Pharmacopoeia,  however,  uses  the  metric  system 
exclusively,  and  it  finds  application  in  all  departments  of  the  U.  S.  govern- 
ment, as  also  for  many  other  purposes.  The  basis  of  the  metric  system  is  a 
quadrant  (one-fourth)  of  the  earth's  circumference.  This  divided  into  ten  mil- 
lion parts  gives  a  measure  of  length  termed  meter  (39.37  inches),  and  this 
unit  of  linear  measure  is  the  basis  for  the  measures  of  extension  and  of  weight. 

Subdivisions  of  all  units  of  metric  measure  are  denoted  by  prefixes  of  Latin 
numerals — i.  e.,  ^  by  deci,  ^Q  by  centi,  -^Q  by  milli ;  while  multiples  are 
denoted  by  prefixes  of  the  Greek  numerals — L  e.,  10  by  deka,  100  by  hecto,  1000 
by  kilo. 

The  unit  of  measure  of  capacity  is  the  cubic  decimeter  called  liter  (1.0567 
U.  S.  quart),  and  the  unit  of  weight  is  the  weight  of  one  cubic  centimeter  of 
water  at  the  temperature  of  its  greatest  density,  4°  C.  (39.2°  F.),  and  this  unit 
is  called  gramme  (15.43-)-  grains).  One  liter  of  water,  equal  to  1000  cubic  centi- 
meters, at  its  greatest  density  weighs  1000  grammes  or  one  kilogram.  While 
gramme  is  the  unit  for  weights  up  to  a  kilogram,  the  latter  is  the  unit  for  all 
larger  weights,  and  is  generally  abbreviated  to  kilo  (2.2046  pounds,  avoirdupois). 

While  in  our  country  for  commercial  purposes  the  avoirdupois  weight  is 
chiefly  used,  the  apothecaries'  weight  is  employed  in  this  country  and  Great 
Britain  in  prescription-writing  by  all  who  do  not  use  the  metric  system.  The 
common  link  connecting  avoirdupois,  troy,  apothecaries',  and  Imperial  weights 
is  the  grain,  which  is  the  same  in  the  four  systems.  (For  table  of  weights  and 
measures,  see  Appendix.) 

Specific  weight  or  specific  gravity  denotes  the  weight  of  a  body, 
as  compared  with  the  weight  of  an  equal  bulk  or  equal  volume  of 
another  substance,  which  is  taken  as  a  standard  or  unit.  This  standard 
adopted  for  all  solids  and  liquids,  if  not  otherwise  stated,  is  water  at 


FUNDAMENTAL   PROPERTIES  OF  MATTER.  33 

a  temperature  of  25°  C.  (77°  F.) ;  that  for  gases  is  either  atmospheric 
air  or,  more  generally,  hydrogen  at  a  temperature  of  0°  C,  (32°  F.). 

Specific  weight  is  generally  expressed  in  numbers  which  denote  how 
many  times  the  weight  of  an  equal  bulk  of  water  is  contained  in  the 
weight  of  the  substance  in  question.  If  we  say  that  mercury  has  a 
specific  gravity  or  density  of  13.6,  or  that  alcohol  has  a  specific  gravity 
of  0.79,  we  mean  that  equal  volumes  of  water,  mercury,  and  alcohol 
represent  weights  in  the  proportion  of  1, 13.6,  and  0.79,  or  100, 1360, 
and  79. 

Since  all  liquids  and  solids  expand  or  contract  with  change  of  tem- 
perature, it  is  very  important  to  note  the  temperature  in  taking  the 
specific  gravity  of  substances.  For  example,  the  specific  gravity  of 
alcohol  is  less  at  25°  C.  than  that  at  15°  C.,  because  alcohol  expands 
with  rise  of  temperature.  Likewise,  at  a  given  temperature,  say  25°  C. 
it  is  greater  when  compared  with  water  at  25°  C.  than  when  com- 
pared with  water  at  4°  C.  or  15°  C.,  because  a  volume  of  water 
weighs  less  at  25°  C.  than  it  does  at  15°  C.  or  4°  C.  Since  the 
change  in  volume  of  solids  with  change  in  temperature  is  much  less 
than  in  the  case  of  liquids,  the  difference  in  specific  gravity  at  differ- 
ent temperatures  is  much  less  noticeable  for  solids  than  for  liquids. 

Density.  Density,  in  physics,  is  defined  as  the  mass  or  quantity 
of  matter  in  a  unit  volume  of  the  substance.  In  the^metric  system 
the  mass  of  a  unit  volume  of  water  at  4°  C.  (39.2°  F.)  is  1  gramme, 
that  is,  the  density  of  water  at  4°  C.  is  unity.  At  any  other  temper- 
ature the  density  of  water  is  less  than  one.  It  can  be  seen  that  when 
the  specific  gravity  of  a  substance  is  determined  by  comparison  with 
water  at  4°  C.,  the  number  expressing  this  specific  gravity  is  identical 
with  the  number  expressing  the  density  of  the  substance. 

When  the  comparison  is  made  with  water  at  any  other  temperature 
than  4°  C.,  the  figures  for  the  specific  gravity  and  the  density  of  a 
substance  are  not  identical,  although  the  difference  between  them  is 
usually  very  small. 

The  specific  gravity  of  solids  heavier  than  water  is  generally  determined  by 
first  weighing  the  substance  in  air  and  then  while  suspended  in  water.  The 
body  will  be  found  to  weigh  less  in  water  because  it  displaces  a  volume  of  water 
equal  to  its  own,  and  loses  a  weight  equal  to  that  of  the  water  displaced.  Con- 
sequently the  relation  between  the  loss  in  weight  and  the  weight  in  air  is  also 
the  relation  between  the  weights  of  equal  volumes  of  water  and  the  substance 
examined.  If,  for  instance,  a  body  is  found  to  weigh  6  grammes  in  air  and  2 
grammes  in  water,  the  loss  being  4  grammes,  then  the  relation  between  the 
weights  of  equal  volumes  of  water  and  the  substance  is  as  4  to  6,  or  1  to  1.5; 
the  latter  being  the  specific  gravity  of  the  substance  examined. 

The  specific  gravity  of  a  solid  soluble  in  water  is  determined  by  weighing  it 
3 


34  CHEMICAL  PHYSICS. 

first  in  air,  then  in  a  liquid  of  known  specific  gravity,  but  having  no  solvent 
action  on  the  substance.  The  weight  of  the  solid  in  air  divided  by  the  weight 
of  the  liquid  displaced  and  the  quotient  then  multiplied  by  the  specific  gravity 
of  the  liquid  employed,  gives  the  specific  weight  of  the  substance  examined. 

The  specific  gravity  of  a  solid  lighter  than  water  is  determined  by  weighing 
it  first  in  air,  then  in  water  attached  to  some  heavy  substance,  the  weight  of 
which  in  water  has  been  ascertained.  The  two  substances  combined  will  weigh 
less  in  water  than  the  heavy  solid  alone.  The  difference  in  weight  between  the 
two  weighings  in  water  added  to  the  weight  of  the  light  substance  in  air  gives 
the  weight  of  water  displaced,  and  this  sum,  divided  into  the  weight  of  the 
solid  in  air,  gives  its  specific  gravity. 

The  method  of  finding  the  specific  gravity  of  a  solid  by  weighing  in  a  liquid 
depends  on  the  Principle  of  Archimedes,  which  says  :  A  body  immersed  in  a  liquid 
loses  a  part  of  its  weight  equal  to  the  weight  of  the  displaced  liquid. 

The  specific  gravity  of  liquids  or  gases  is  determined  by  weighing  in  suitable 
glass  flasks  equal  volumes  of  the  standard  substance  and  the  body  to  be  examined. 
The  weight  of  the  latter  divided  by  the  weight  of  the  standard  substance  gives 
the  specific  gravity. 

Small  glass  flasks  suitably  arranged  for  taking  the  specific  gravity  of  liquids 
are  known  as  pycnometers. 

A  second  method  by  which  the  specific  gravity  of  liquids  may  be  determined 
is  by  means  of  the  instruments  known  as  hydrometers,  or,  if  made  for  some 
special  purposes,  as  alcoholometers,  urinometers,  alkalimeters,  lactometers,  etc. 

Hydrometers  are  instruments  generally  made  of  glass  tubes, 
having  a  weight  at  the  lower  end  to  maintain  them  in  an  upright 
position  in  the  fluid  to  be  tested  as  to  specific  gravity,  and  a  stem 
above,  bearing  a  scale.  The  principle  upon  which  their  construction 
depends  is  the  fact  that  a  solid  substance  when  placed  in  a  liquid 
heavier  than  itself  displaces  a  volume  of  this  liquid  equal  to  the 
whole  weight  of  the  displacing  substance.  The  hydrometer  will 
consequently  sink  lower  in  liquids  of  lower  specific  gravity  than  in 
heavier  ones,  as  the  instrument  has  to  displace  a  larger  bulk  of  liquid 
in  the  lighter  than  in  the  heavier  liquid  in  order  to  displace  its  own 
weight. 

"Weight  of  gases.  We  have  so  far  considered  the  gravity  of  solids 
and  liquids  only,  and  the  next  question  will  be :  Do  gases  also  possess 
weight — are  they  also  attracted  by  the  earth  ?  The  fact  that  a  gas, 
when  generated  or  liberated,  expands  in  every  direction,  might  indi- 
cate that  the  molecules  of  a  gas  have  no  weight,  are  not  attracted  by 
the  earth.  A  few  simple  experiments  will,  however,  show  that  gases, 
Jike  all  other  substances,  have  weight.  Thus  a  flask  from  which  the 
atmospheric  air  has  been  removed  will  weigh  less  than  the  same  flask 
when  filled  with  atmospheric  air  or  any  other  gas. 


FUNDAMENTAL  PROPERTIES  OF  MATTER.  35 

Barometer.  A  second  method  by  which  may  be  demonstrated 
the  fact  that  atmospheric  air  possesses  weight,  is  by  means  of  the 
barometer.  The  atmosphere  is  that  ocean  of  gas  which  encircles  the 
earth  with  a  layer  some  50  or  100  miles  in  thickness,  exerting  a  con- 
siderable pressure  upon  all  substances  by  its  weight.  The  instru- 
ments used  for  measuring  that  pressure  are  known  as  barometers,  and 
the  most  common  form  of  these  is  the  mercury  barometer.  It  may 
be  constructed  by  filling  with  mercury  a  glass  tube  closed  at  one  end 
(and  about  three  feet  long)  and  then  inverting  it  in  a  vessel  contain- 
ing mercury,  when  it  will  be  found  that  the  mercury  no  longer  fills 
the  tube  to  the  top,'  but  only  to  a  height  of  about  30  inches,  leaving 
a  vacuum  above.  The  column  of  mercury  is  maintained  at  this 
height  by  the  pressure  of  the,  atmosphere  upon  the  surface  of  the 
mercury  in  the  vessel ;  a  column  of  mercury  about  30  inches  high 
must  consequently  exert  a  pressure  equal  to  the  pressure  of  a  column 
of  the  atmosphere  of  the  same  diameter  as  that  of  the  mercury 
column. 

As  the  weight  of  a  column  of  mercury,  having  a  base  of  one  square 
inch  and  a  height  of  about  30  inches,  is  equal  to  about  15  pounds,  a 
column  of  atmosphere  having  also  a  base  of  one  square  inch  must  also 
weigh  15  pounds.  In  other  words,  the  atmospheric  pressure  is  equal 
to  about  15  pounds  to  the  square  inch,  or  about  one  ton  to  the  square 
foot.  This  enormous  pressure  is  borne  without  inconvenience  by  the 
animal  frame  in  consequence  of  the  perfect  uniformity  of  the  pressure 
in  every  direction. 

A  barometer  may  be  constructed  of  other  liquids  than  mercury,  but  as  the 
height  of  the  column  must  always  bear  an  inverse  proportion  to  the  density  of 
the  liquid  used,  the  length  of  the  tube  required  must  be  greater  for  lighter 
liquids.  As  water  is  13.6  times  lighter  than  mercury,  the  height  of  a  water 
column  to  balance  the  atmospheric  pressure  is  13.6  times  30  inches,  or  about  34 
feet,  which  would,  therefore,  be  the  height  of  the  column  of  water  required. 

It  is  evident  that  the  pressure  of  the  atmosphere  is  equal  to  the  weight  of  a 
column  of  mercury,  and  also  that  this  weight  is  directly  proportional  to  the 
length  of  the  mercury  column.  Hence,  different  atmospheric  pressures  can  be 
compared  in  terms  of  the  length  of  the  mercury  column  of  the  barometer, 
instead  of  in  terms  of  pounds  per  square  inch.  For  example,  at  a  pressure  of 
15  pounds  per  square  inch,  the  mercury  column  is  about  30  inches,  while  at  a 
pressure  of  10  pounds  per  square  inch,  it  is  20  inches.  ^  The  ratio  of  the  pres- 
sures in  pounds  is  10 :  15  or  2  :  3,  and  the  ratio  of  the  mercury  columns  is  20  :  30 
or  2  : 3,  which  is  the  same.  This  fact  is  of  interest  in  experiments  in  which 
gas  volumes  are  dealt  with,  because  calculations  have  to  be  made  involving  a 
ratio  of  pressure*,  and  since  this  ratio  is  the  same  as  that  of  the  lengths  of  the 
mercury  column  corresponding  to  the  pressures,  it  simplifies  matters  greatly  to 
express  pressures  in  terms  of  the  length  of  a  column  of  mercury. 


36  CHEMICAL  PHYSICS. 

Changes  in  the  atmospheric  pressure.  The  height  of  the  mer- 
cury column  in  a  barometer  is  not  the  same  at  all  times,  but  varies 
within  certain  limits.  These  variations  are  due  to  a  number  of  causes 
disturbing  the  density  of  the  atmosphere,  and  are  chiefly  atmospheric 
currents,  temperature,  and  the  amount  of  moisture  contained  in  the 
atmosphere. 

As  the  height  and  with  it  the  density  of  the  atmosphere  diminishes 
gradually  from  the  level  of  the  sea  upward,  the  height  of  the  mercury 
column  will  be  lower  in  localities  situated  at  an  elevation.  This 
diminution  of  pressure  is  so  constant  that  the  barometer  is  used  for 
estimating  elevations. 

Porosity.  We  have  seen  that  the  molecules  of  any  substance  are 
not  in  absolute  contact,  but  that  there  are  spaces  between  them  which 
we  call  intermolecular  spaces ;  the  property  of  matter  to  have  spaces 
between  the  particles  composing  it  is  known  as  porosity. 

In  the  case  of  solids,  these  spaces  or  pores  are  scmetimes  of  con- 
siderable size,  visible  even  to  the  naked  eye,  as,  for  instance,  in 
charcoal,  while  in  most  cases  they  cannot  be  discovered,  even  by  the 
microscope.  That  even  apparently  very  dense  substances  are  porous, 
can  be  demonstrated  by  the  fact  that  liquids  may  be  pressed  through 
metallic  disks  of  considerable  thickness,  that  gases  may  be  caused  to 
pass  through  plates  of  metal  or  stone,  that  solids  dissolve  in  liquids 
without  showing  a  corresponding  increase  in  volume  of  the  solution 
thus  obtained,  and,  finally,  also  by  the  fact  that  substances  suffer  ex- 
pansion or  contraction  in  consequence  of  increased  or  diminished 
heat,  or  in  consequence  of  mechanical  pressure. 

Surface.  In  every-day  life  the  expression  "surface"  refers  to  that 
part  of  a  substance  which  is  open  to  our  senses,  visible  and  measur- 
able ;  but  from  a  more  scientific  point  of  view,  we  have  also  to  take 
into  consideration  those  surfaces  which,  in  consequence  of  porosity, 
extend  to  the  interior  of  matter  and  are  invisible  to  our  eyes  and 
absolutely  immeasurable  by  instruments. 

Surface-action.  Attraction  acts  differently  under  different  condi- 
tions, and,  accordingly,  we  assign  different  names  to  it.  We  call  it 
cohesion  when  it  acts  between  molecules,  gravitation  when  acting 
between  masses,  and  surface-action  or  surface-attraction  when  the 
attraction  is  exerted  either  by  the  visible  surface  or  by  that  surface 
which  pervades  the  whole  interior  of  matter.  The  phenomena  caused 


FUNDAMENTAL  PROPERTIES  OF  MATTER.  37 

by  this  surface-action  are  extremely  manifold,  and  some  are  of  suffi- 
cient interest  to  be  taken  into  consideration. 

Adhesion.  Most  solid  substances,  when  immersed  in  water, 
alcohol,  or  many  other  liquids,  become  moist ;  immersed  in  mercury, 
they  remain  dry.  We  explain  this  fact  by  saying  that  the  surfaces 
of  most  solid  substances  exert  an  attraction  for  the  particles  of  such 
liquids  as  water  and  alcohol  to  such  an  extent  that  these  particles 
adhere  to  the  surface  of  the  solids.  Such  an  attraction,  however, 
does  not  manifest  itself  for  the  particles  of  mercury.  This  form  of 
surface-attraction  by  which  liquids  are  caused  to  adhere  to  solids  is 
called  adhesion. 

This  adhesion  may  be  noticed  also  between  two  plates  having  plane 
surfaces.  A  drop  of  water  pressed  between  these  plates  will  cause 
them  to  adhere  to  each  other.  The  application  and  use  of  glue  and 
mucilage,  our  methods  of  writing  and  painting,  the  welding  together 
of  pieces  of  metal,  etc.,  depend  on  this  kind  of  surface  action. 

Capillary  attraction.  While  it  is  the  general  rule  that  liquids 
in  vessels  present  a  horizontal  surface,  this  rule  does  not  hold  good 
near  the  sides  of  the  vessel.  When  the  liquids  wet  the  vessel,  as  in 
the  case  of  water  in  a  glass  vessel,  the  surface  is  somewhat  concave 
in  consequence  of  the  attraction  of  the  glass  surface  for  the  particles 
of  water ;  on  the  contrary,  when  the  liquids  do  not  wet  the  vessel,  as 
in  the  case  of  mercury  in  a  glass  vessel,  the  surface  is  somewhat 
convex.  The  smaller  the  diameter  of  the  vessel  holding  the  liquids, 
the  more  concave  or  convex  will  the  surface  be.  If  a  narrow  tube  is 
placed  in  a  liquid,  this  surface-action  will  be  more  striking,  and  it 
will  be  found  that  a  liquid  wetting  the  tube  will  not  only  have  a 
completely  concave  surface,  but  the  level  of  the  liquid  stands  per- 
ceptibly higher  in  the  tube  than  the  level  of  the  liquid  outside. 
Substances  not  wetting  the  tube  will  show  the  reverse  action,  namely, 
the  surface  inside  of  the  tube  will  be  convex,  and  will  be  below  the 
level  of  the  liquid  outside. 

The  attraction  of  the  surface  of  tubes  for  liquids,  manifesting 
itself  in  the  concave  shape  of  the  surface  and  in  the  elevation  of  the 
liquid  near  the  tube,  is  known  as  capillary  attraction.  Capillary 
elevations  and  depressions  depend  upon  the  diameter  of  the  tube, 
temperature,  and  the  nature  of  the  liquid.  The  narrower  the  tube, 
the  higher  the  elevation  or  the  lower  the  depression ;  both  are 
diminished  by  increased  temperature.  Capillary  elevations  and 


38  CHEMICAL  PHYSICS. 

depressions,  all  other  circumstances  being  equal,  are  inversely  pro- 
portional to  the  diameters  of  the  tubes. 

Defining  the  phenomena  of  capillary  attraction  more  scientifically, 
we  may  say  that  the  adhesive  force  of  glass,  wood,  etc.,  for  water  and 
most  other  liquids  exceeds  the  cohesive  force  acting  between  the 
molecules  of  these  liquids,  while  in  mercury  the  cohesive  force  pre- 
dominates over  the  adhesive. 

The  rise  or  fall  of  liquids  in  capillary  tubes  is  explained  thus  :  There  is  an 
attraction  between  the  particles  in  the  surface  of  a  liquid  which  causes  the 
surface  to  act  like  a  stretched  membrane.  It  requires  force  to  separate  the 
particles  in  the  surface  and  this  force  is  spoken  of  as  the  surface  tension  of  the 
liquid.  Proof  of  this  tension  is  seen  in  the  fact  that  insects  can  stand  on  water 
without  breaking  through,  and  that  an  oily  needle  can  float  on  water  although 
it  is  heavier  than  it.  Another  principle  in  physics  is  that  a  stretched  surface 
of  a  spherical  form  exerts  a  force  toward  the  center  of  curvature  of  the  surface, 
and  tends  to  contract  toward  the  center.  Illustrations  of  this  are  seen  in  the 
fact  that  drops  of  liquids  assume  a  spherical  form,  and  that  soap  bubbles  con- 
tract when  the  air  in  the  interior  of  them  is  allowed  to  escape.  Now,  when  a 
fine  tube  is  dipped  into  a  liquid  that  wets  it,  particles  of  the  liquid  are  drawn 
up  by  adhesion  of  the  glass,  thus  causing  a  curved  surface,  which,  acting  like  a 
membrane,  draws  up  the  particles  below  it  by  cohesion.  The  liquid  rises  until 
the  weight  of  the  column  counterbalances  the  cohesion  between  the  particles 
in  the  curved  surface,  that  is,  the  surface  tension.  Thus  we  see  also  why  liquids 
rise  higher  in  fine  tubes  than  wider  ones,  since  it  requires  a  shorter  column 
of  liquid  of  greater  diameter  to  equal  in  weight  a  longer  column  of  smaller 
diameter.  Moreover,  since  surface  tension  of  liquids  diminishes  as  tempera- 
ture rises,  we  see  why  capillary  elevation  diminishes  as  temperature  increases. 
The  same  kind  of  argument  will  explain  why  liquids  which  do  not  wet  a  tube, 
for  example,  mercury,  will  sink  in.  the  tube  below  the  level  of  the  liquid 
outside. 

Familiar  examples  of  capillary  phenomena  are  the  action  of  lamp-wicks, 
the  rise  of  water  in  wood,  sponges,  bibulous  paper,  sand,  sugar,  and  the  rise  of 
sap  in  the  vessels  of  plants. 

Surface-attraction  of  solids  for  gases.  Any  dry  solid  sub- 
stance, carefully  weighed,  will,  after  having  been  exposed  to  a  higher 
temperature,  show  a  decrease  in  weight  while  yet  warm.  Upon 
cooling,  the  original  weight  will  be  restored.  This  fact  cannot  be 
explained  otherwise  than  that  some  substance  or  substances  must 
have  been  expelled  by  heat,  and  that  this  substance  or  these  sub- 
stances are  reabsorbed  on  cooling. 

This  is  actually  the  case,  and  the  substances  expelled  and  reab- 
sorbed are  the  gaseous  constituents  of  the  atmospheric  air,  chiefly  the 
aqueous  vapor. 

Every  solid  substance  upon  our  earth  condenses  upon  its  surface 


FUNDAMENTAL  PROPERTIES  OF  MATTER.  39 

more  or  less  of  the  gaseous  constituents  of  the  atmosphere.  This 
condensation  takes  place  upon  the  outer  as  well  as  upon  the  inner 
surface.  The  amount  of  gas  absorbed  depends  upon  the  nature  of 
the  gas  as  well  as  upon  the  nature  of  the  absorbing  solid.  Some  of 
the  so-called  porous  substances,  such  as  charcoal,  generally  condense 
or  absorb  larger  quantities  than  solids  of  a  more  dense  and  compact 
structure.  Heat,  as  stated  above,  counteracts  this  absorbing  power. 

The  absorptive  power  of  charcoal  for  gases  varies  with  the  nature  of  the 
charcoal  and  the  gas  absorbed,  as  will  be  seen  from  the  following  table: 

Unit  volume  of  charcoal  absorbs — 

Boxwood.  Cocoanut. 

Ammonia  gas 90       vols.  172  vols. 

Hydrochloric  acid  gas 85         " 

Sulphur  dioxide 65          ' 

Hydrogen  sulphide 55          ' 

Nitrogen  monoxide 40          '  86  vols. 

Carbon  dioxide 35          '  68     " 

Ethylene  gas 35          '  75     " 

Carbon  monoxide    . 9.42      '  21     " 

Oxygen 9.25     '  18     " 

Nitrogen 7.5       '  15     " 

Hydrogen 1.75     '  4     " 

Pine  charcoal  has  about  one-half  the  absorptive  power  of  boxwood  char- 
coal. Platinum  sponge  absorbs  about  250  times  its  volume  of  oxygen.  Other 
porous  substances,  as  meerschaum,  gypsum,  silk,  etc.,  are  also  very  absorbent. 

Surface-attraction  of  solids  for  liquids  or  for  solids  held  in 
solution.  When  a  mixture  of  different  liquids,  or  a  mixture  of 
different  solids  dissolved  in  a  liquid,  is  brought  in  contact  with  or 
filtered  through  a  porous  solid  substance,  such  as  charcoal  or  bone- 
black,  it  will  be  found  that  the  surface  of  the  solid  substance  retains 
a  certain  amount  of  the  liquids  or  of  the  solids  held  in  solution,  and 
that  it  retains  more  of  one  kind  than  of  another. 

It  is  this  peculiarity  of  surface-attraction  which  is  made  use  of  in 
purifying  drinking-water  by  allowing  it  to  pass  through  charcoal. 
Bone-black  is  similarly  used  for  decolorizing  sugar-syrup  and  other 
liquids. 

Absorbing-  power  of  liquids.  In  a  similar  manner  as  in  the 
case  of  solids,  liquids  also  exert  an  attraction  for  gases.  When  a 
gas  is  condensed  within  the  pores  or  upon  the  surface  of  a  solid,  or 
when  it  is  taken  up  and  condensed  by  a  liquid,  we  call  the  process 
absorption.  This  absorbing  power  of  different  liquids  for  different 
gases  varies  greatly ;  it  is  facilitated  by  low  temperature  and  high 


40  CHEMICAL  PHYSICS. 

pressure,  and  counteracted  by  high  temperature  and  removal  of 
pressure.  Thus  :  One  volume  of  water  absorbs  at  ordinary  tempera- 
ture and  pressure  about  0.03  volume  of  oxygen,  1  volume  of  carbon 
dioxide,  30  volumes  of  sulphur  dioxide,  and  800  volumes  of  ammonia. 

Diffusion.  When  a  cylindrical  glass  vessel  has  been  partially 
filled  with  water,  and  alcohol,  which  is  specifically  lighter  than 
water,  is  poured  upon  it,  care  being  taken  to  prevent  a  mixing  of  the 
two  liquids,  so  as  to  form  two  distinct  layers,  it  will  be  found  that 
after  a  certain  lapse  of  time  the  two  liquids  have  mixed  with  each 
other,  particles  of  water  having  entered  the  alcohol  and  particles  of 
alcohol  the  water,  until  a  uniform  mixture  of  the  two  liquids  has 
taken  place.  Upon  repeating  the  experiment  with  a  layer  of  water 
over  a  column  of  solution  of  common  salt,  it  will  again  be  found  that 
the  two  liquids  gradually  enter  one  into  the  other  until  a  uniform 
salt  solution  has  been  formed. 

In  a  similar  manner,  two  or  more  gases  introduced  into  a  vessel  or 
a  room  will  readily  mix  with  each  other.  This  gradual  passage  of 
one  liquid  into  another,  of  a  dissolved  substance  into  another  liquid, 
or  of  one  gas  into  another  gas,  is  called  diffusion. 

The  rate  of  diffusion  is  different  for  different  substances.  Saline  substances 
may  be  divided  into  a  number  of  equidiffusive  groups.  The  quantity  of  a  sub- 
stance diffused  varies  also  with  the  temperature.  Thus,  the  rate  of  diffusion 
of  hydrochloric  acid  at  49°  C.  is  2.18  times  that  at  15°  C.  The  following  table 
gives  the  approximate  times  of  equal  diffusion  for  the  substances  named : 

Hydrochloric  acid 1.0       Magnesium  sulphate     ....      7.0 

Sodium  chloride 2.3       Albumin      49.0 

Sugar 7.0       Caramel 98.0 

Magnesium  sulphate  is  one  of  the  least  diffusible  saline  substances,  yet  it 
diffuses  7  times  faster  than  albumin  and  14  times  faster  than  caramel. 

Diffusion  is  exhibited  also  by  solids,  even  at  ordinary  temperature.  Sir  "\V. 
Roberts- Austen  placed  gold  and  lead  in  contact  four  years  at  18°  C.,  and 
found  the  surfaces  united.  Gold  had  penetrated  the  lead  to  more  than  o  milli- 
meters from  the  surface,  while  within  0.75  millimeter  from  the  surface  gold 
was  found  at  the  rate  of  1  oz.  6  pwt.  per  ton,  which  would  be  profitable  to 
extract. 

The  phenomena  of  diffusion  can  be  explained  only  on  the  theory  that  matter 
is  made  up  of  particles  or  molecules  in  motion.  They  are  one  of  the  strong 
links  in  the  chain  of  evidence  upon  which  the  molecular  theory  of  matter  is 
founded. 

Osmose.  Dialysis.  This  diffusion  takes  place  also  when  two 
liquids  are  separated  by  a  porous  diaphragm,  sucb  as  bladder  or 
parchment  paper,  and  it  is  then  called  osmose,  endosmosis,  or  dialysis. 


FUNDAMENTAL  PROPERTIES  OF  MATTER.  41 

The  apparatus  used  for  dialysis  is  called  a  dialyzer  (Fig.  1 5),  and 
consists  usually  of  a  glass  cylinder,  open  at  one  end  and  closed  at  the 
other  by  the  membrane  to  be  used  as  the  separating  medium.     This 
vessel  is  placed  into  another,  and 
the  two  liquids  are  introduced  into 
the   two   vessels.     If  the   inner 
vessel  be  filled  with  a  salt  solution 
and  the  outer  one  with  pure  water, 
it  will  be  found  that  part  of  the 
salt  solution  passes  through  the 
membrane  into  the  water,  whilst 
at  the   same   time  water   passes 
over  to  the  salt  solution 

On  subjecting  different  sub- 
stances to  this  process  of  dialysis,  it  has  been  found  that  some  sub- 
stances pass  through  the  membrane  with  much  greater  facility  or  in 
larger  quantities  than  others,  and  that  some  do  not  pass  through  at 
all.  As  a  general  rule,  crystallizable  substances  pass  through  more 
freely  than  amorphous  substances.  Those  substances  which  do  not 
pass  through  membranes  in  the  process  of  dialysis  are  known  as  col- 
loids, those  which  diffuse  rapidly  crystalloids. 

Capillary  attraction,  or,  more  generally  speaking,  surface-attrac- 
tion, is  undoubtedly  to  some  extent  the  cause  of  the  phenomena  of 
osmose,  the  surface  of  the  diaphragm  exercising  an  attraction  upon 
the  liquids. 

Diffusion  through  the  membrane  will  not  take  place  unless  the 
membrane  is  in  contact  with  water,  and,  moreover,  its  limit  will  be 
reached  when  the  concentration  outside  is  the  same  as  that  inside  the 
dialyzer.  Hence,  a  large  quantity  of  water  should  be  on  the  outside 
and  often  renewed.  Generally,  water  flows  through  the  membrane 
toward  the  denser  liquid,  which  increases  in  volume,  but  alcohol  and 
ether  are  exceptions.  They  act  like  liquids  which  are  denser  than 
water.  In  the  case  of  acids,  water  flows  either  into  the  acids  or  from 
the  acids,  according  as  they  are  more  or  less  dilute.  When  a  dilute 
alcohol  is  kept  for  a  time  in  a  bladder  the  volume  diminishes,  but 
the  alcoholic  strength  increases.  The  reason  of  this  is,  no  doubt, 
that  the  bladder  permits  the  water  to  pass  rather  than  the  alcohol. 

An  interesting  effect  of  osmosis  is  seen  in  the  purgative  action  of 
magnesium  sulphate.  A  solution  of  this  salt  is  not  readily  absorbed 
and  causes  a  flow  of  water  from  the  intestinal  bloodvessels  by 
osmosis,  which,  together  with  the  direct  stimulating  action  of  the 
salt  to  peristalsis,  causes  purging  action.  All  strong  saline  solutions, 


42  CHEMICAL  PHYSICS. 

above  0.7  per  cent.,  abstract  liquids  from  animal  tissues  when  in  con- 
tact with  them. 

Diffusion  of  gases.  A  diffusion  similar  to  that  of  liquids  takes 
place  also  when  two  different  gases  are  separated  from  each  other  by 
some  porous  substance,  such  as  burned  clay,  gypsum,  and  others. 

It  has  been  found  that  specifically  lighter  gases  diffuse  with  greater  rapidity 
than  the  heavier  ones.  The  quantities  of  two  different  gases  which  diffuse 
into  one  another  in  a  given  time  are,  as  a  general  rule,  inversely  as  the  square 
roots  of  their  specific  gravities.  Oxygen  is  sixteen  times  as  heavy  as  hydrogen  ; 
when  the  two  gases  diffuse,  it  will  be  found  that  four  times  as  much  hydrogen 
has  penetrated  into  the  oxygen  as  of  the  latter  gas  into  the  hydrogen.  This 
regularity  in  the  diffusion  of  gases  is  expressed  in  the  Law  of  Graham,  thus: 
The  velocity  of  the  diffusion  of  any  gas  is  inversely  proportional  to  the  square 
root  of  its  density. 

Indestructibility.  All  matter  is  indestructible — i.  e.,  cannot  pos- 
sibly be  destroyed  by  any  means  whatever,  and  this  property  is  known 
as  indestructibility.  Form,  shape,  appearance,  properties,  etc.,  of 
matter  may  be  changed  in  many  different  ways,  but  the  matter  itself 
can  never  be  annihilated.  Apparently,  matter  often  disappears,  as, 
for  instance,  when  water  evaporates  or  oil  burns;  but  these  apparent 
destructions  indicate  simply  a  change  in  the  form  of  matter;  in  both 
cases  gases  are  formed,  which  become  invisible  constituents  of  the 
atmospheric  air,  and  can,  therefore,  not  be  seen  for  the  time  being, 
but  may  be  recoudensed  or  rendered  visible  in  various  ways. 

Not  only  is  matter  indestructible,  energy  also  partakes  of  this 
property.  This  is  expressed  in  the  Law  of  the  conservation  of  energy, 
which  says  that  in  a  limited  system  of  bodies  no  gain  or  loss  of 
energy  is  ever  observed.  But  energy  may  be  converted  from  one 
form  into  some  other  form.  Motion  may  be  converted  into  heat,  and 
heat  into  motion,  or  this  motion  into  electrical  energy  and  chemical 
energy.  In  fact,  all  the  different  forms  of  energy  are  convertible  one 
into  the  other,  theoretically,  without  loss.  This  fact  is  spoken  of  as 
the  Law  of  the  correlation  of  energies. 

QUESTIONS. — Define  matter,  force,  and  energy.  Describe  the  character- 
istic properties  of  matter  in  the  solid,  liquid,  and  gaseous  states.  State  the  dif- 
ference between  amorphous,  crystalline,  polymorphous,  and  isomorphous  sub- 
stances. State  the  laws  of  Boyle  and  Avogadro.  Explain  the  terms  mass  and 
molecule.  What  are  cohesion,  adhesion,  and  gravitation?  Mention  instances 
of  their  action.  Give  a  definition  of  weight  and  of  specific  weight.  Explain 
construction  and  use  of  the  mercury  barometer.  Define  capillary  attraction, 
absorption,  diffusion,  and  osmose ;  give  instances  illustrating  their  action. 
What  is  meant  by  saying  that  matter  and  energy  are  indestructible? 


HEAT.  43 

2.  HEAT. 

Motion  of  molecules.  If  we  place  over  a  gas-flame  a  vessel  con- 
taining a  lump  of  ice  of  the  temperature  of  0°  C.,  or  32°  F.,  the  ice 
melts  and  becomes  converted  into  water ;  but  if  we  measure  with  a 
thermometer  the  temperature  of  the  water  at  the  moment  when  the 
last  particle  of  ice  is  melted,  we  still  find  it  at  the  freezing-point, 
0°  C.  or  32°  F.  From  the  position  of  the  vessel  over  the  flame,  as 
well  as  from  .the  fact  that  the  ice  has  been  liquefied,  we  know  that 
the  vessel  and  its  contents  have  absorbed  heat.  Yet  vessel  and  water 
show  the  same  temperature  as  before.  If  the  heat  of  the  flame  is 
allowed  to  continue  its  action  on  the  ice-cold  water,  the  thermometer 
will  soon  indicate  a  rapid  absorption  of  heat  until  the  temperature 
reaches  100°  C.  or  212°  F.  Then  the  water  begins  to  boil  and 
escapes  in  the  form  of  steam,  but  the  temperature  remains  stationary 
until  the  last  particle  of  water  has  disappeared. 

There  must  be,  consequently,  some  relation  between  the  state  of 
aggregation  of  a  substance  and  that  agent  which  we  call  heat.  It  was 
the  heat  which  liquefied  the  ice,  it  was  the  heat  which  converted  the 
liquid  water  into  steam  or  gaseous  water.  Yet  the  water,  having 
absorbed  considerable  heat  during  the  process  of  melting,  shows  a 
temperature  of  0°  C.  (32°  F.),  and  the  steam  also  having  absorbed 
large  quantities  of  heat,  shows  100°  C.  (212°  F.),  the  temperature  of 
boiling  water.  A  certain  amount  of  heat  has  consequently  been  lost 
or  at  least  hidden.  What  has  become  of  it? 

To  answer  this  we  must  first  examine  a  little  further  into  the 
nature  of  heat.  It  is  a  well-known  fact  that  when  two  solid  bodies 
are  rubbed  together  heat  is  produced.  Ice  may  be  melted  and  water 
boiled  by  friction ;  wood  may  be  made  to  ignite  by  rubbing  it  suita- 
bly. It  is  found  by  accurate  experiments  that  there  is  an  intimate 
relation  between  the  amount  of  heat  generated  and  the  amount  of 
work  done  to  generate  it.  The  amount  of  heat  is  always  equivalent 
to  the  amount  of  work  expended.  This  fact  is  one  of  the  manifesta- 
tions of  the  law  known  as  the  law  of  the  correlation  of  energy. 

Many  other  illustrations  of  production  of  heat  by  the  expenditure 
of  work  could  be  given,  and  all  would  point  to  the  conclusion  that 
heat  is  associated  in  some  way  with  the  condition  of  the  small  parti- 
cles of  which  substances  are  made  up — i.  e.,  the  molecules. 

It  is  believed  that  the  molecules  of  all  bodies  are  in  motion. 
Those  of  gases  are  perfectly  free  to  move  in  any  direction,  while  in 
liquids  and  solids  they  are  restricted  in  their  motion.  In  solids  the 


44  CHEMICAL  PHYSICS. 

molecules  are  held  rigidly  in  a  fixed  position  and  can  vibrate  only 
back  and  forth.  The  molecules  thus  have  a  certain  energy  of  motion 
which  is  called  kinetic  energy,  and  in  liquids  and  solids  an  energy  of 
position  also,  known  as  potential  energy.  This  potential  energy  is 
due  to  the  position  or  molecular  arrangement  of  the  particles,  and  to 
make  a  change  in  this  necessitates  the  overcoming  of  the  forces 
which  hold  the  molecules  in  place  by  an  expenditure  of  energy  from 
some  outside  source. 

Thus  it  is  believed  that  whenever  heat  energy  is  added  to  a  body 
it  either  goes  to  increasing  the  motion  of  molecules — i.  e.,  the  kinetic 
energy,  or  to  making  a  change  in  the  relative  positions  of  the  mole- 
cules— i.  e.,  in  their  potential  energy,  or  to  both. 

When  the  motion  of  the  molecules  is  increased — i.  e,  when  the 
kinetic  energy  is  increased — there  is  a  rise  in  temperature,  which  we 
can  measure  by  a  thermometer.  What  we  call  temperature  is  the 
degree  or  intensity  of  the  sensible  heat  of  a  body. 

On  the  other,  hand,  heat  is  absorbed  whenever  solids  pass  into  the 
liquid  state ;  or  liquids  into  the  gaseous  state.  This  fact  is  often 
made  use  of  in  producing  artificial  cold.  Thus,  liquefied  ammonia  is 
employed  in  the  manufacture  of  ice,  the  required  low  temperature 
being  produced  by  evaporation  of  the  ammonia.  Similarly,  the  heat 
absorbed  during  the  liquefaction  of  snow  or  powdered  ice  by  an 
admixture  of  common  salt  and  the  liquefaction  of  the  latter  through 
solution  serve  for  generating  a  low  temperature.  The  action  of  the 
various  freezing-mixtures  depends  on  this  principle. 

Latent  heat.  Sometimes  heat  may  be  added  to  a  body  without 
any  change  of  temperature,  as  above  in  the  case  of  the  melting  of  ice 
and  the  boiling  of  water.  In  such  cases  it  is  believed  that  the  heat 
added  is  absorbed  in  changing  the  relative  arrangement  of  the  mole- 
cules, which  change  must  evidently  take  place  in  passing  from  solid 
to  liquid  water  and  from  liquid  to  gaseous  water.  This  will  account 
for  the  apparent  loss  of  heat  in  melting  ice  or  in  boiling  water.  It 
is  lost  only  to  our  senses,  and  exists  in  another  form  as  potential 
energy  of  the  molecules ;  hence  it  is  called  latent  heat. 

This  latent  heat  is  given  out  again  when  the  molecules  return  to 
their  former  arrangement.  Hence  steam  in  condensing  to  water,  and 
water  in  assuming  the  solid  state,  give  off  large  quantities  of  heat. 

Sources  of  heat.  Our  principal  source  of  heat  is  the  sun.  Other 
sources  are  :  The  interior  of  the  earth,  the  high  temperature  of  which 
is  made  manifest  by  the  existence  of  volcanoes  and  by  the  increase  of 


SEAT.  45 

temperature  noted  in  boreholes  sunk  into  the  earth's  crust ;  mechan- 
ical actions,  as  friction  and  compression  ;  electric  currents ;  and,  finally, 
chemical  action,  as  witnessed  in  the  ordinary  processes  of  combustion 
and  of  animal  life. 

Up  to  within  a  few  years  ago  the  principal  method  for  generating  heat  de- 
pended on  combustion.  Heat  generated  by  electricity  is  now  at  our  command. 
The  introduction  of  the  electric  furnace  has  provided  means  for  obtaining  much 
higher  temperatures  than  formerly.  It  is  through  these  modern  means  that 
temperatures  are  produced  sufficiently  high  for  the  liquefaction  or  volatilization 
of  all  substances. 

On  the  other  hand,  during  the  last  few  years  methods  have  been  invented 
for  producing  very  much  lower  temperatures  than  formerly.  Several  gases 
which  were  believed  to  be  permanent  can  now  be  liquefied,  and  even  solidified. 

Heat  Effects.  The  most  familiar  changes  resulting  from  the 
application  of  heat,  that  is,  from  the  absorption  of  heat  energy,  are 
those  affecting  the  volume,  the  temperature,  and  the  molecular  arrange- 
ment or  physical  state  of  matter.  These  changes  do  not  take  place 
independently,  but  accompany  one  another.  Chemical  changes  are 
also  often  produced  by  application  of  heat,  but  these  are  considered 
in  chemistry. 

Increase  of  volume  by  heat.  As  a  general  rule^  the  volume  of 
any  mass  increases  with  increase  in  its  temperature,  but  this  increase  is 
not  alike  for  all  matter.  Gases  expand  more  than  liquids,  liquids 
more  than  solids,  and  of  the  latter  the  metals  more  than  most  other 
solid  substances.  While  the  expansion  of  any  two  or  more  different 
solids  or  liquids  is  not  alike,  gases  show  a  fixed  regularity  in  this 
respect,  namely,  all  gases  without  exception  expand  or  contract 
alike  when  the  temperature  is  raised  or  lowered  an  equal  number  of 
degrees. 

This  expansion  or  contraction  of  gases  is  0.3665  per  cent.,  or  ^  of  their 
volume  at  0°  C.  for  every  degree  centigrade ;  thus  100  volumes  of  air  become 
100.3665  volumes  when  heated  from  0°  to  1°  C.,  or  136.65  when  heated  from 
0°  to  100°  C.  This  regularity  in  the  expansion  and  contraction  of  gases  is 
expressed  in  the  Law  of  Charles,  which  says  :  If  the  pressure  remain  constant,  the 
volume  of  a  gas  increases  regularly  as  the  temperature  increases,  and  decreases  as 
the  temperature  decreases.  If  heat  be  applied  to  a  gas  confined  in  a  closed  ves- 
sel and  be  thus  prevented  from  expanding,  the  increase  of  heat  will  manifest 
itself  as  pressure,  which  rises  with  the  same  regularity  as  shown  for  expansion, 
viz.,  0.3665  per  cent,  for  every  degree  centigrade. 

It  often  becomes  necessary  to  reduce  the  volume  of  a  gas  measured  at  any 
temperature  and  at  any  pressure  to  the  volume  it  would  occupy  at  0°  C.  and 
760  mm.  pressure,  which  have  been  adopted  as  normal  temperature  and  press- 


46  CHEMICAL  PHYSICS. 

ure.  The  method  for  making  this  calculation  is  given  in  the  paragraph  on 
gas-analysis,  for  which  see  Index. 

In  expansion  of  solids  and  liquids  the  heat  energy  applied  is  utilized  partly 
in  forcing  the  molecules  farther  apart  or  overcoming  cohesion,  partly  in  raising 
the  temperature  or  giving  the  molecules  greater  motion,  and  partly  in  doing 
external  work,  that  is,  work  that  the  expanding  body  does  in  raising  a  load  that 
may  be  resting  upon  it,  or  overcoming  any  force  exerted  against  it.  In  the 
expansion  of  gases,  there  being  no  cohesion  between  the  molecules,  the  heat 
energy  is  utilized  in  raising  the  temperature  and  in  doing  work  by  the  gas  against 
external  force. 

Expansion  is  a  very  important  thing  which  must  be  taken  into  account  by 
constructors,  for  example,  of  bridges,  railroad  beds,  etc.  Also  in  very  careful 
physical  measurements,  expansion  of  glass  apparatus,  solutions,  barometers, 
etc.,  must  be  carefully  noted. 

Increase  in  temperature  by  heat.  As  was  said  above,  the  present 
molecular  theory  of  matter  regards  the  molecules  as  in  motion,  and 
the  result  of  this  energy  of  motion  is  what  we  call  temperature,  or 
intensity  or  degree  of  heat.  Anything  that  increases  this  motion  of 
the  molecules,  causes  a  rise  of  temperature.  Our  skin  is  possessed  of 
nerve  structures  by  which  we  can  judge  whether  a  body  is  hot  or 
cold  or  whether  one  body  is  hotter  than  another,  but  these  are  not 
delicate  enough  to  make  quantitative  distinctions  between  tempera- 
tures. For  this  purpose  we  make  use  of  instruments  called 

Thermometers.  In  these,  use  is  made  of  the  fact  that  bodies  expand 
while  the  temperature  rises,  and  that  the  expansion  is  proportional  to 
rise  of  temperature.  Thermometers,  therefore,  measure  directly  only 
expansion,  and  indirectly  degrees  of  heat,  but  the  expansion  is  used 
as  a  measure  of  the  degree  of  heat.  The  most  common  thermometer 
is  the  mercury  thermometer.  This  instrument  may  be  easily  con- 
structed by  filling  a  glass  tube,  having  a  bulb  at  the  lower  end,  with 
mercury,  and  heating  the  tube  until  the  mercury  boils  and  all  air  has 
been  expelled,  when  the  tube  is  sealed.  It  is  then  placed  in  steam 
arising  from  water  boiling  actively  under  normal  barometric  pressure 
of  760  millimeters  of  mercury,  and  the  point  to  which  the  mercury 
rises  is  marked  B.  P.  (boiling-point)  ;  after  which  it  is  placed  in  melting 
ice,  and  the  point  to  which  the  mercury  sinks  is  marked  F.  P.  (freezing- 
point).  The  distance  between  the  boiling-  and  freezing-points  is  then 
divided  into  100  degrees  in  the  so-called  centigrade  or  Celsius 
thermometer,  into  80  degrees  in  the  Reaumur  thermometer,  and  into 
180  degrees  in  the  Fahrenheit  thermometer.  The  inventor  of  the 
latter  instrument,  Fahrenheit,  commenced  counting  not  from  the 
freezing-point,  but  32  degrees  below  it,  which  causes  the  freezing- 


HEAT. 


47 


point  to  be  at  32°,  and  the  boiling-point  at  180  degrees  above  it,  or  at 
212°.  (Fig.  16.)  Degrees  of  temperature  below  the  zero  point  of 
either  instrument  are  designated  by  — ,  i.  e.y  minus. 


100 


0° 


FIG.  16. 


....BE— 


212 


As  100  degrees  centigrade  are  equivalent  to  180  degrees  Fahrenheit,  it  follows 
that  1  degree  C.  =  1.8  degree  F.,  or  1  degree  F.  = 
\%  degree  C.  In  converting  the  degrees  from  one 
scale  to  the  other  it  must  be  remembered  that  the 
zero  point  of  Fahrenheit  is  32  degrees  below  the 
zero  on  the  centigrade  scale.  Consequently,  in 
converting  the  reading  on  a  Fahrenheit  scale  into 
centigrade  degrees,  82  degrees  must  be  deducted, 
or,  vice  versa,  be  added,  before  the  calculation  can 
be  made.  In  other  words,  to  convert  Fahrenheit 
into  centigrade :  Subtract  32  and  divide  by  1.8  ;  to 
convert  centigrade  into  Fahrenheit :  Multiply  by 
1.8  and  add  32. 


Recording  or  self-registering  thermome- 
ters. One  kind  of  these  instruments  is  so  con- 
structed as  to  show  the  highest,  the  other  the 
lowest  temperature  to  which  the  thermometer  had 
been  exposed  from  the  time  it  was  last  adjusted. 
The  physician's  fever  thermometer  is  a  maximum 
recording  thermometer  with  a  scale  ranging  usu- 
ally from  94°  to  112°  F.  These  thermometers 
have  near  the  bulb  a  constriction  in  the  tube 
which  breaks  the  column  of  mercury  when  it  con- 
tracts. Consequently  the  thin  column  of  mercury 
retains  its  position  on  cooling,  but  may  be  forced 
back  through  the  constriction  into  the  bulb  by 
shaking  the  instrument. 


p-p. 


32° 


Centigrade.       Fahrenheit. 
Thermometric  scales. 


Absolute   temperature.      If  differences 

of  temperature  are  due  to  faster  or  slower  motion  of  molecules,  we 
can  well  imagine  that  there  is  a  limit  in  both  directions.  Where  the 
limit  is  to  be  found  for  rapidity  of  motion  is  unknown,  but  good  rea- 
sons lead  us  to  believe  that  we  know  the  point  at  which  molecular 
motion  ceases. 

One  of  the  reasons  which  lead  us  to  believe  in  the  correctness  of 
this  statement  is  the  Law  of  Charles,  above  mentioned.  In  accord- 
ance with  this  law,  it  follows  that  if  a  mass  of  air  at  0°  C.  is  heated, 
its  volume  is  increased  -3-7-3-  of  the  original  volume  for  every  degree 
its  temperature  is  raised.  At  273°  C.  its  volume  is  consequently 


48  CHEMICAL  PHYSICS. 

doubled,  and  at  546°  C.  tripled.  If  a  mass  of  air  is  cooled  below 
0°  C.,  its  volume  is  diminished  ^^  of  its  volume  for  every  degree 
its  temperature  is  lowered.  Consequently,  if  its  volume  were  to 
continue  to  decrease  at  that  rate  until  it  reached  — 273°  C.,  mathe- 
matically speaking  its  volume  would  become  nothing.  In  fact, 
the  air  long  before  this  low  temperature  had  been  reached  would 
cease  to  be  a  gas — would  first  liquefy,  then  solidify,  and  at  the  tem- 
perature of  — 273°  C.  would  become  a  compact  mass  in  which  the 
molecules  were  at  absolute  rest.  This  point  of  no  heat  is  called  the 
absolute  zero,  and  temperature  reckoned  from  this  point  is  called 
absolute  temperature. 

The  fraction  -^7-3-  is  called  the  coefficient  of  expansion  for  centigrade 
degrees,  while  ^y  is  the  coefficient  of  expansion  for  degrees  of 
Fahrenheit.  The  absolute  temperature  may  be  found  by  adding  273 
to  the  reading  on  a  centigrade  thermometer,  or  459  to  the  reading  on 
a  Fahrenheit  thermometer. 

While  the  temperature  of  absolute  zero  may  never  be  obtainable  by  man, 
so  much  successful  work  in  the  field  of  low  temperatures  has  been  done  lately 
that  temperatures  within  9  degrees  of  absolute  zero  have  been  observed. 

In  chemistry  and  other  fields,  temperature  is  often  indicated  by  such  phrases 
as  red  heat,  white  heat,  etc.  The  following  table  gives  approximately  the 
degrees  corresponding  to  such  expressions : 

Incipient  red  heat 525°  C.  (977°  F.). 

Dark  red  heat 700°  C.  (1292°  F.). 

Bright  red  heat 950°  C.  (1742°  F.). 

Yellow  heat 1100°  C.  (2012°  F.). 

Incipient  white  heat     .    , 1300°  C.  (2372°  P.). 

White  heat 1500°  C.  (2732°  F.). 

Mechanical  equivalent  of  heat.  While  thermometers  indicate 
the  intensity  of  heat,  it  is  often  desirable  to  measure  heat  quantities. 
These  determinations  are  based  on  the  intimate  relationship  existing 
between  heat  and  mechanical  or  molecular  motion,  which  are  capable 
of  being  converted  one  into  the  other.  Thus,  friction  produces  heat 
and  heat  produces  motion  in  the  steam  engine.  Heat,  through  its 
power  to  produce  motion,  can  do  work,  and  the  amount  of  work  it 
can  do  depends  on  the  quantity  of  heat. 

The  unit  of  heat  quantity  now  universally  used  in  chemical  and  physiological 
work  is  the  calorie.  It  is  the  amount  of  heat  consumed  in  raising  1  kilogram 
of  water  from  0°  C.  to  1°  C.  (or,  approximately,  1  pound  of  water  4  degrees  of 
Fahrenheit).  If  this  amount  of  heat  could  all  be  made  to  do  mechanical  work. 


HEAT.  49 

it  would  be  sufficient  to  raise. 420  kilograms  1  meter  high,  or  3000  pounds  1  foot 
high — L  e.,  the  calorie  is  equivalent  to  420  kilogram-meters,  or  3000  foot  pounds. 
The  heat  generated  by  combustion  is  determined  in  the  laboratory  by  means  of 
an  apparatus  known  as  the  calorimeter.  This  is  generally  so  constructed  that 
a  definite  weight  of  substance  may  be  burned  in  a  chamber  surrounded  by  cold 
water.  The  rise  in  temperature  of  this  known  quantity  of  water  serves  as  the 
basis  for  calculation. 

Specific  heat.  Equal  weights  of  different  substances  require  dif- 
ferent quantities  of  heat  to  raise  them  to  the  same  temperature.  For 
instance  :  The  same  quantity  of  heat  which  is  sufficient  to  raise  1 
pound  of  water  from  60°  to  70°  will  raise  the  temperature  of  1 
pound  of  olive  oil  from  60°  to  80°,  or  that  of  2  pounds  of  olive  oil  from 
60°  to  70°.  Olive  oil  consequently  requires  only  one-half  of  the  heat 
necessary  to  raise  an  equal  weight  of  water  the  same  number  of  degrees. 
As  water  has  been  selected  as  the  standard  for  comparison,  we  may 
say  that  specific  heat  is  the  heat  required  to  raise  a  certain  weight  of 
a  substance  a  certain  number  of  degrees,  compared  with  the  heat 
required  to  raise  an  equal  weight  of  water  the  same  number  of 
degrees. 

The  heat  required  to  raise  1  gramme  of  water  1  degree  centigrade 
is  usually  taken  as  the  unit  of  comparison.  On  thus  comparing 
olive  oil,  we  find  its  specific  heat  to  be  J.  If  we  say  the  specific 
heat  of  mercury  is  ^-,  we  indicate  that  equal  quantities  of  heat  will 
be  required  to  raise  1  pound  of  water  or  32  pounds  of  mercury  1 
degree,  or  that  the  heat  which  raises  1  pound  of  water  1  degree  will 
raise  1  pound  of  mercury  32  degrees. 

Conduction  of  heat.  When  the  end  of  a  metallic  bar  is  heated, 
a  rise  in  its  temperature  is  soon  noticed  at  a  distance  from  the  heated 
part.  This  transfer  of  heat  from  some  source,  for  instance  from  a 
flame  to  a  cold  substance,  is  practically  a  transfer  of  motion  from 
more  rapidly  moving  molecules  to  those  moving  more  slowly.  It 
may  be  compared  to  the  motion  imparted  to  a  billiard  ball  at  rest  or 
moving  slowly  by  another  ball  propelled  with  greater  velocity.  The 
more  rapidly  moving  ball  will  lose  part  of  its  velocity  in  imparting 
motion  to  the  other  ball.  Similarly  the  rapidly  moving  molecules  of 
the  hot  body  in  transferring  motion  to  molecules  moving  slowly  in 
the  cold  body  lose  some  of  their  velocity — i.  e.,  the  hot  body  itself 
becomes  cooler.  The  expression  "  cooling  off"  must  never  be  under- 
stood to  imply  a  transfer  of  cold,  but  always  a  removal  of  heat.  In 
taking  a  cold  bath,  or  in  applying  an  ice-bag  to  a  fever  patient,  we 


50  CHEMICAL  PHYSICS. 

bring  about  a  slower  molecular  motion  in  the  tissues  exposed  to  the 
cold  material. 

The  direct  transfer  of  molecular  motion  is  called  conduction  of  heat, 
but  in  examining  various  materials  we  find  that  they  show  a  great 
difference  in  their  power  to  conduct  heat.  For  instance,  if  we  hold  in 
a  flame  the  end  of  a  glass  rod,  it  may  be  made  red-hot,  while  but  little 
increase  of  heat  will  be  perceived  at  the  other  end.  We  accordingly 
distinguish  between  good  and  bad  conductors  of  heat.  Gases  and 
liquids  (mercury  excepted)  are  bad  conductors,  and  of  the  solids 
the  metals  are  the  best.  The  following  table  gives  the  comparative 
heat-conducting  power  of  a  number  of  substances,  that  of  silver  being 
taken  as  the  standard,  and  represented  by  1 : 


Copper  .        .        .        .0.96 

Iron  .        .        .     -   .     0.20 

Stone  ....     0.006 
Water  0.002 


Glass    ....  0.0005 

Wool   ....  0.00012 

Paper  ....  0.000094 

Air  .  0.000049 


Convection.  On  fastening  a  piece  of  ice  to  the  bottom  of  a  test- 
tube,  and  filling  this  with  water  and  holding  it  over  a  flame  in  such 
a  manner  that  only  the  upper  portion  of  the  tube  is  heated,  the  water 
may  be  made  to  boil  before  the  ice  has  been  melted.  The  reason  is 
that  water  is  a  bad  conductor  of  heat.  If  the  flame  be  applied  to  the 
lower  part  of  the  test-tube,  the  whole  mass  of  water  will  remain 
cold  until  the  ice  has  melted,  and  the  temperature  will  then  rise 
evenly  through  the  mass  of  water,  because  the  heated  lighter  par- 
ticles will  move  upward  while  the  colder  ones  move  downward. 
Thus  ascending  and  descending  currents  are  produced,  equalizing  the 
temperature.  The  term  convection  is  applied  to  this  method  of  con- 
veying and  distributing  heat.  Air  or  gases  behave  similarly,  and 
this  fact  is  of  practical  interest  in  the  construction  of  chimneys  and 
in  heating  and  ventilating  buildings. 

Radiation  of  heat.  A  heated  body,  for  instance  a  ball  of  red-hot 
iron,  suspended  in  the  air  or  in  a  vacuum  will  heat  objects  near  by. 
If  a  screen  is  placed  between  these  objects  and  the  heated  body,  no 
rise  in  temperature  is  noticed.  Heat  is  here  propagated  through 
space  in  straight  lines,  commonly  spoken  of  as  heat  rays. 

In  order  to  explain  these  phenomena,  as  also  others  closely  related 
to  them,  such  as  those  of  light  and  electricity,  it  has  been  necessary 
to  assume  the  existence  of  some  agent  that  serves  as  a  means  for  this 
propagation.  This  hypothetical  agent,  called  ether,  is  a  medium  of 


HEAT.  51 

extreme  tenuity  and  elasticity  supposed  to  be  diffused  throughout 
the  universe,  and  indeed  permeating  all  matter. 

Similarly  as  waves  of  water  are  generated  by  dropping  a  stone  into 
it,  and  as  sound  waves  are  produced  in  air  by  causing  it  to  vibrate, 
so  heat  waves  are  produced  in  the  ether  whenever  it  is  disturbed  by 
the  rapid  molecular  motion  of  a  heated  body. 

While  our  views  regarding  the  nature  of  ether  are  of  a  hypothetical 
character,  there  can  be  no  doubt  of  the  existence  of  these  heat  waves. 
Indeed,  their  length,  their  velocity,  and  many  other  features  have 
been  fully  determined ;  they  obey  largely  the  same  laws  which  have 
been  established  for  light  waves — i.  e.,  when  striking  against  a  body 
they  are  generally  reflected,  transmitted,  diffused,  or  absorbed.  It 
is  this  absorption  of  heat,  as  we  call  it,  which  causes  the  heating- 
effects  through  space.  It  may  be  compared  to  the  motion  that  can 
be  imparted  to  an  object  floating  on  still  water.  By  disturbing  the 
water,  as  by  dropping  a  stone  into  it  at  a  distance  from  the  floating 
object,  concentric  ripples  or  waves  pass  from  the  point  where  the 
water  was  disturbed,  and  in  striking  the  floating  object  cause  it  to 
move.  Similarly  waves  of  heat  pass  from  a  heated  body  through 
the  ether  in  every  direction,  and  in  striking  against  a  body  cause  its 
molecules  to  move  faster — i.  e.,  render  it  warmer.  It  is  by  this 
process  that  heat  is  transmitted  from  the  sun  to  the  earth. 

Change  in  molecular  state.  As  was  pointed  out  above  in  the  discus- 
sion of  the  nature  of  heat,  it  requires  energy  to  bring  about  a  change 
in  the  relative  position  of  the  molecules  of  a  substance,  which  is 
called  internal  work.  This  is  true  for  solids  and  liquids,  but  not  for 
gases,  since  there  is  practically  no  cohesion  between  the  particles  of  a 
gas,  and  so  no  work  is  required  to  change  the  position  of  the  particles. 
Several  familiar  phenomena  involve  change  in  the  molecular  state. 

Fusion  or  melting-.  This  name  is  applied  to  the  process  by  which 
a  solid  passes  into  the  liquid  state.  When  a  liquid  passes  into  the  solid 
state,  the  process  is  known  as  solidification.  As  a  rule,  when  solids 
are  heated,  they  begin  to  melt  at  a  definite  temperature,  which  is  known 
as  the  fusion-point  or  melting-point.  Conversely,  when  liquids  are 
cooled,  they  begin  to  solidify  at  a  definite  temperature,  which  is  iden- 
tical with  the  melting-point  of  the  solid.  Moreover,  the  temperature 
remains  constant  as  long  as  fusion  or  solidification  continues. 

Solids  that  are  individuals  (not  mixtures)  and  are  perfectly  pure  as 
far  as  they  melt  without  decomposition,  have  definite  or  sharp  melting- 


52  CHEMICAL  PHYSICS. 

points,  which  fact  is  utilized  in  chemistry  extensively  for  determining 
the  identity  of  substances  and  their  purity.  A  small  amount  of 
impurity  in  a  substance  often  causes  a  notable  change  in  its  melting- 
point  and  the  temperature  rises  between  the  beginning  and  the  end  of 
melting,  instead  of  remaining  constant. 

Some  solids,  like  wax  and  paraffin,  which  are  mixtures,  do  not  remain 
at  the  same  temperature  during  fusion,  and  in  such  cases  the  melting- 
point  is  taken  as  the  average  of  the  temperatures  at  which  fusion  and 
solidification  begin. 

The  determination  of  the  melting-point  is  carried  out  by  introducing 
a  column  about  J  inch  long  of  the  finely  powdered  substance  into  a 
capillary  glass  tube  sealed  at  one  end,  and  attaching  this  to  the  bulb 
of  a  thermometer.  The  latter  is  then  dipped  into  a  liquid  of  high 
boiling-point  and  the  temperature  is  slowly  raised.  The  instant  the 
substance  melts,  the  temperature  is  noted,  which  is  the  melting-point, 
often  abbreviated  m.-p. 

Latent  heat  of  fusion.  This  is  the  number  of  heat  units  (calories) 
required  to  make  1  gramme  of  a  substance  fuse.  Different  substances 
have  different  latent  heats  of  fusion,  but  water  (ice)  has  the  greatest. 
To  melt  1  gramme  of  ice  at  0°  C.  to  water  at  0°  C.  requires  80  calories, 
or  as.  much  heat  becomes  latent  as  will  raise  1  gramme  of  water  from 
0°  C.  to  80°  C. 

Change  of  volume  by  fusion.  When  any  solid  fuses,  a  change  in 
volume  always  occurs.  Some  substances  expand  during  fusion,  for 
example,  bismuth,  wax  ;  others  contract,  for  example,  brass,  cast-iron, 
ice.  When  a  solid  floats  in  its  own  liquid,  this  is  evidence  that  it  con- 
tracts on  fusion,  because  the  density  of  the  solid  is  less  than  that  of  its 
liquid.  When  a  solid  sinks  in  its  own  liquid,  there  is  expansion  on 
fusion. 

Evaporation  and  boiling-.  Many  liquids,  even  some  solids, 
evaporate  or  assume  the  gaseous  state  at  nearly  all  temperatures. 
Water  and  ice,  mercury,  camphor,  and  many  other  substances  vapor- 
ize at  temperatures  which  are  far  below  their  regular  boiling-points. 
This  fact  is  to  be  explained  by  the  assumption  that  during  the  rapid 
vibratory  motion  of  the  particles  of  these  masses,  some  particles  are 
driven  from  the  surface  beyond  the  sphere  to  which  the  surrounding 
molecules  exert  an  attraction,  and  thus  intermingle  with  the  mole- 
cules of  the  surrounding  air. 


HEAT.  53 

This  evaporation,  which  takes  place  at  various  temperatures  and  at 
the  surface  only,  is  not  to  be  confounded  with  boiling,  which  is  the 
rapid  conversion  of  a  liquid  into  a  gas  at  a  fixed  temperature  with 
the  phenomena  of  ebullition,  due  to  the  formation  of  gas  in  the  mass 
of  liquid.  Boiling-point  may,  therefore,  be  defined  as  the  highest 
point  to  which  any  liquid  can  be  heated  under  the  normal  pressure  of 
one  atmosphere. 

A  liquid  in  a  closed  space  evaporates  until  a  definite  pressure  is 
attained  by  the  vapor  at  a  fixed  temperature,  when  the  liquid  and 
vapor  remain  in  equilibrium.  When  this  limit  is  reached  the  vapor 
is  said  to  be  "  saturated."  If  the  temperature  is  increased,  more 
liquid  evaporates  and  the  pressure  increases.  If  the  temperature  of 
a  saturated  vapor  falls,  some  vapor  is  condensed  to  liquid,  or  if  the 
pressure  is  increased,  some  vapor  will  also  condense  to  liquid.  At  a 
given  temperature  a  saturated  vapor  exerts  a  definite  pressure, 
which  is  different  for  different  vapors.  Thus,  in  terms  of  a  column 
of  mercury,  at  20°  C.  (68°  F.),  water  vapor  exerts  a  pressure  of  17 
mm.,  alcohol  vapor,  60  mm.,  and  ether  vapor,  450  mm. 

As  a  rule,  in  experiments  where  gas  volumes  are  measured,  the  gas  is  satu- 
rated with  aqueous  vapor,  which  has  to  be  taken  into  account  in  making  calcu- 
lations. If  a  volume  of  gas  saturated  with  water-vapor  is  measured  at  atmo- 
spheric pressure,  the  tension  of  the  gas  alone  is  the  difference  between  the 
barometric  pressure  and  the  tension  of  the  saturated  water-vapor  at  the  given 
temperature. 

Tension  of  Saturated  Water-vapor  (Regnault). 


Temperature, 

Tension 

Temperature, 

Tensic 

Centigrade. 

in  mm. 

Centigrade. 

in  nan 

0°  

4.6 

16°  

13.5 

1°  

4.9 

17°  

14.4 

2°  

5.3 

18°  

15.4 

3°  

5.7 

19°  

16.3 

4°  

61 

20°  

17.4 

5°  

6.5 

21°  

,    18.5 

6°  

7.0 

22° 

19.7 

7°  

7.5 

23°  

20.9 

8°  

8.0 

24°  

22.2 

9°  

8.5 

25°  

23.6 

]0°  

9.1 

26°  

,       S  .    .    .    .  25.0 

11°  

9.8 

27°  

26.5 

12°  

10.4 

28°  

28.1 

13°  

11.1 

29°  

29.8 

14°  

.    .        .    .  11.9 

30°  

31.6 

15°  ... 

12.7 

Distillation  is  the  conversion   of  a  liquid  into  a  gas,  and  the  con- 


54  CHEMICAL  PHYSICS. 

densation  of  the  gas  into  a  liquid,  by  causing  the  gas  to  pass  through 
a  cooling  device  or  condenser,  whereby  the  heat  that  was  made  latent 
and  is  necessary  for  maintaining  the  gaseous  state,  is  extracted.  Dis- 
tillation is  usually  carried  on  by  boiling  the  liquid  under  atmospheric 
pressure,  but  sometimes  it  is  done  under  reduced  pressure  by  exhaust- 
ing the  air  from  the  apparatus,  and  then  the  liquid  boils  at  a  much 
lower  temperature.  Distillation  is  a  very  useful  process  for  purify- 
ing liquids,  as,  thereby,  non- volatile  impurities  may  be  easily  removed 
from  liquids.  Moreover,  mixtures  of  liquids  having  different  boiling- 
points  may  be  separated  approximately  into  the  constituents  by  dis- 
tillation (see  Fractional  Distillation  in  Index). 

The  process  of  vaporization,  known  as  sublimation,  has  been  men- 
tioned under  Crystals,  page  21. 

The  determination  of  the  boiling-point  is  best  done  in  a  flask,  as 
shown  in  Fig.  69,  If  inflammable  or  noxious  vapors  are  likely  to 
be  evolved,  they  may  be  condensed  to  the  liquid  state  by  connecting 
the  exit  tube  of  the  flask  with  a  condenser.  It  is  important  that  the 
thermometer  should  not  be  immersed  in  the  liquid,  but  should  be 
surrounded  only  by  the  vapor  of  the  liquid.  Heat  is  applied  to  the 
flask  until  the  liquid  assumes  a  state  of  active  ebullition,  and  when 
vapor  is  escaping  freely  and  the  temperature  ceases  to  rise,  the  latter 
is  noted.  This  is  the  boiling-point  of  the  liquid  at  the  atmospheric 
pressure  prevailing  at  the  time. 

Pure  liquids,  under  the  same  pressure,  always  have  the  same  boil- 
ing-points, and  this  property  is  very  important  in  chemistry  in 
judging  of  the  purity  of  liquids.  Impure  liquids  not  only  have  dif- 
ferent boiling-points  from  the  pure  substances,  but  also  the  tempera- 
ture rises  during  boiling  instead  of  remaining  constant. 

The  boiling-points  of  different  liquids  vary  widely.  Thus,  mer- 
cury boils  at  357°  C.,  water  at  100°  C.,  alcohol  at  78°  C.,  chloroform 
at  61°  C.,  ether  at  35°  C.,  oxygen  at  -182.5°  C.,  hydrogen  at 
—252.5°  C.,  under  standard  atmospheric  pressure. 

Latent  heat  of  vaporization.  When  a  liquid  passes  to  the  gas- 
eous state,  heat  energy  is  absorbed  or  becomes  latent^  and,  conversely, 
when  a  vapor  is  condensed  to  a  liquid,  the  same  heat  energy  is  given 
out.  If  the  heat  is  not  added  to  the  liquid  from  the  outside,  the  heat 
is  absorbed  from  the  liquid  itself  during  vaporization  and  its  tem- 
perature falls.  The  sensation  of  cold  produced  by  the  evaporation 
of  water,  alcohol,  ether,  chloroform,  etc.,  from  the  skin  is  familiar  to 
every  one.  It  is  by  evaporation  of  moisture  from  the  skin  that  the 


HEAT.  55 

temperature  of  our  body  is  kept  normal  in  heated  weather.  A  thin 
glass  beaker,  containing  ether  and  resting  on  some  water  on  a  glass 
plate,  may  quickly  be  frozen  to  the  plate  by  passing  a  rapid  current 
of  air  through  the  ether. 

The  number  of  calories  of  heat  required  to  vaporize  1  gramme  of 
any  liquid  at  a  given  temperature  is  called  its  latent  heat  of  vaporiza- 
tion. The  latent  heat  of  steam  at  100°  C.  is  535.9  calories,  that  is, 
it  requires  as  much  heat  to  convert  1  gramme  of  water  at  100°  C. 
into  steam  at  100°  C.,  as  would  raise  535.9  grammes  of  water  1°  C. 
in  temperature.  Steam  has  the  largest  latent  heat  of  all  known  sub- 
stances, hence,  its  value  in  warming  houses,  etc.,  by  the  steam-heat- 
ing process. 

Influence  of  pressure  on  state  of  aggregation.  We  have  seen 
that  the  volume  of  a  substance,  and,  more  especially,  of  a  gas,  depends 
upon  pressure  and  temperature,  an  increase  of  pressure  or  decrease  of 
temperature  causing  the  volume  to  become  smaller.  We  learned  also 
that  liquids  may  be  converted  into  gases,  and  that  this  conversion 
takes  place  at  a  certain  fixed  temperature,  called  the  boiling-point. 
This  point,  however,  changes  with  the  pressure.  An  increased  pres- 
sure will  raise,  a  decreased  pressure  will  lower,  the  boiling-point. 


Thus,  water  boils  at  the  normal  pressure  of  one  atmosphere  at  100°  C.  (212° 
F.),  but  it  will  boil  at  a  lower  temperature  on  mountains  in  consequence  of  the 
diminished  atmospheric  pressure.  If  the  pressure  be  increased,  as,  for  instance, 
in  steam-boilers,  the  boiling-point  will  be  raised.  Thus,  the  boiling-point  of 
water  under  a  pressure  of  two  atmospheres  is  at  122°  C.  (251°  F.),  of  five  atmo- 
spheres at  153°  C.  (307°  F.),  of  ten  atmospheres  at  180°  C.  (356°  F.).  A  differ- 
ence of  pressure  of  10  millimeters  from  the  normal  atmospheric  pressure  (760 
mm.)  produces  a  difference  of  0.36°  C.  in  the  boiling-point  of  water,  100°  C. 


QUESTIONS.— What  is  the  view  in  regard  to  the  nature  of  heat?  What  is 
meant  by  sensible  heat  and  latent  heat?  What  is  the  law  in  regard  to  expan- 
sion of  gases  when  heated?  Explain  the  construction  of  a  thermometer  and 
the  principle  on  which  it  depends.  What  Fahrenheit  temperature  corresponds 
to  50°  C.,  to  130°  C.,  to  — 40°  C.?  What  Centigrade  temperature  corresponds 
to  167°  F.,  to  311°  F.,  to  14°  F.  ?  What  is  meant  by  absolute  temperature? 
Give  a  definition  of  the  following :  Calorie,  specific  heat,  conduction,  convec- 
tion, and  radiation  of  heat.  Define  melting  and  state  how  the  melting-point  is 
determined  ;  define  latent  heat  of  fusion.  State  the  difference  between  evapo- 
ration and  boiling.  What  is  distillation  and  sublimation?  What  is  meant  by 
latent  heat  of  vaporization  ?  What  is  the  influence  of  pressure  on  the  boiling- 
point  of  liquids  ? 


56  CHEMICAL  PHYSICS. 

3.  LIGHT. 

Light  a  form  of  energy.  It  has  been  shown  in  the  preceding 
chapter  that  a  heated  body  sends  forth  waves  through  the  ether, 
which  in  striking  a  cooler  body  cause  its  molecules  to  vibrate  more 
quickly — i.  e.,  heat  it  to  a  higher  temperature.  But  an  increased 
molecular  motion  may  produce  other  effects  than  heat,  as  we  may 
observe  by  heating  an  iron  bar,  which,  when  sufficiently  hot,  will 
emit  light.  That  light  is  different  in  effect  from  heat,  though  both 
come  from  the  same  hot  body,  may  be  observed  in  the  action  of 
luminously  hot  bodies  on  certain  chemicals ;  for  example,  the  silver 
salts,  which  undergo  a  change  in  their  chemical  composition.  The 
action  of  sunlight  on  photographic  plates  is  an  excellent  illustration. 

The  explanation  of  these  phenomena  is  that  ether  waves  of  diverse 
characters  produce  different  effects.  Thus,  the  waves  coming  to  us 
from  the  sun  may  affect  the  sense  of  touch,  and  we  call  the  effect 
heat ;  they  may  affect  the  sense  of  sight,  and  we  term  it  light ;  or 
they  may  affect  the  composition  of  matter,  when  we  speak  of  it  as 
chemical  action.  But  in  all  these  results  we  have  simply  different 
manifestations  of  some  form  of  radiant  energy.  Light  is  that  form 
of  energy  which  may  be  appreciated  by  the  organ  of  vision. 

Color.  Both  heat-  and  light-producing  waves  or  oscillations  are 
propagated  through  ether  with  the  same  velocity,  viz.,  at  the  rate  of 
300,000  kilometers,  or  186,000  miles,  per  second  ;  but  the  waves 
differ  in  regard  to  length  and  in  the  amplitude  of  vibration.  Waves 
of  a  particular  limited  range  of  frequency  (477,000,000  millions  to 
699,000,000  millions  per  second)  when  falling  upon  the  eye  produce 
a  sensation  of  light.  Of  these,  the  slowest — i.  e.,  the  waves  with 
the  least  frequency  and  the  greatest  wave-length — produce  a  sensa- 
tion of  red  light ;  as  the  frequency  increases,  the  sensation  produced 
by  them  is  successively  that  which  is  termed  orange,  yellow,  green, 
blue,  indigo,  and  violet  light. 

Ether  waves  of  frequency  too  limited  to  be  visible  are  called  infra- 
red  waves  ;  they  have,  however,  great  heating  power  when  falling 
upon  a  substance.  On  the  other  hand,  there  are  waves  of  greater 
frequency  than  those  which  produce  a  sensation  of  violet ;  they  are 
also  invisible,  but  have  the  power  of  producing  chemical  action  ;  they 
are  called  ultra-violet  or  actinic  waves.  There  is  no  inherent  difference 
between  any  of  the  different  kinds  of  waves  here  mentioned  ;  indeed, 
they  all  may  be  produced  at  the  same  time  by  the  same  body. 

In  what  is  called  daylight  there  is  a  mixture  of  waves  of  different 
frequencies,  affecting  our  eye  simultaneously  in  such  a  manner 


LIGHT. 


57 


that  none  of  the  specific  colors  predominates.  The  reason  that  even 
under  the  influence  of  this  white  light  most  objects  show  a  distinct 
color  is  not,  as  might  be  supposed,  an  inherent  color  possession  of 
these  objects,  but  an  effect  of  the  light.  Without  light  all  objects 
are  black  —  i.  <?.,  without  light  there  is  no  color.  There  is  a  great 
diversity  in  the  behavior  of  different  substances  toward  white  light. 
It  may  either  be  absorbed  or  reflected,  or  partly  absorbed  and  partly 
reflected.  If  all  be  absorbed,  black  is  the  result  ;  if  all  rays  except 
the  red  ones  be  absorbed,  the  body  appears  red,  etc. 

Not  only  has  the  number  of  wave  oscillations  per  second  been 
determined,  but  also  their  length.  The  longest  waves  are  those  pro- 
ducing heat  ;  the  shortest  ones  are  the  actinic  waves.  Between  them 
are  the  light  waves  ranging  from  650  millionths  of  a  millimeter  in 
length  for  red  light,  to  442  millionths  of  a  millimeter  in  length  for 
violet  light. 

Light  rays.  Light  travels  through  homogeneous  media,  as  air, 
water,  and  glass,  in  straight  lines,  and  a  very  narrow  cylinder  of  light 
is  called  a  ray,  beam,  or  pencil  of  light.  Those  bodies  which  readily 
transmit  luminous  rays  are  said  to  be  transparent,  those  not  trans- 
mitting light  are  called  opaque,  while  translucent  bodies  are  those 
permitting  light  to  pass  through  them  to  a  limited  extent. 

A  body  may  be  self-luminous,  like  the  sun  or  a  flame  ;  or  it  may 
be  luminous  by  reflected  light,  like  the  moon  or  any  object  that  is 
illuminated  by  daylight  or  by  any  luminous  body. 

Light  of  itself  is  invisible,  as  can  be  shown  by  admitting  a  sun- 
beam through  a  small  hole  into  a  dark  room.  If  the  air  be  free 
from  dust,  the  beam  is  invisible  ;  but  if  the  eye,  or  any  object  upon 

which  it  mav  strike,  is  placed  in  its  path, 

~  V. 
we  are  made   aware   of   its  presence,  not 

by  seeing  the  light,  but  by  seeing  the  ob- 
ject which  emits  it  or  intercepts  it. 

Reflection.  When  a  ray  of  light  strikes 
a  mirror  or  a  polished  surface  obliquely 
we  notice  that  a  ray  of  light  is  thrown  off 

or  reflected  from  the  mirror.     On  measuring 
,1  ,      .  ,_..        «  „.  ,     ,  . 

the  angle  ^  (Fig.  17)  made  by  the  entering 
or  incident  ray  CB  and  a  perpendicular  NB,  and  the  angle  r  made 
by  the  reflected  ray  AB  and  the  perpendicular,  they  will  be  found 
equal.  In  other  words,  in  plane  mirrors  the  angle  of  incidence  is 
always  equal  to  the  angle  of  reflection. 


FIG.  17. 


Reflection. 


58 


CHEMICAL   PHYSICS. 


Upon  this  reflection  depends  the  formation  of  the  image  seen  in  mirrors. 
If  a  reflecting  surface  were  an  absolutely  smooth  plane,  it  would  be  invisible, 
and  we  would  see  in  it  simply  the  images  of  other  subjects.  Most  objects  are 
not  bounded  by  absolutely  smooth  surfaces,  and,  consequently,  the  light  which 
falls  upon  them  is  scattered  or  diffused,  thus  rendering  them  visible  in  all 
directions. 

Refraction.  While  a  light  ray  travels  in  a  straight  line  through 
homogeneous  media,  the  ray  is  bent  when  passing  from  a  medium 
of  one  density  to  that  of  another  density,  as  from  air  to  glass  or  to 
water.  Under  these  conditions,  unless  the  ray  enter  perpendicularly, 

it  is  bent  out  of  its  course,  still  moving, 
however,  in  a  straight  path  in  the 
second  medium,  but  in  a  different 
direction  from  that  in  the  first.  This 
bending  of  rays  is  known  as  refrac- 
tion. It  is  refraction  which  causes  a 
straight  stick,  when  held  obliquely 
in  clear  water,  to  appear  bent  at  the 
point  of  entering  the  water. 

In  Fig.  18,  SI  represents  a  ray  of 
light  entering  a  denser  medium — say 
a  plate  of  glass — with  parallel  sides. 
Here  the  ray  is  bent  toward  the  per- 
pendicular N'R ;  on  leaving  the  denser  medium  and  re-entering  the 
air  it  is  again  bent,  but  away  from  the  perpendicular  to  such  an 
extent  that  the  rays  SI  and  US'  (or  rather  their  extensions)  are 
parallel  to  one  another. 

Refraction  through  prisms.  A  prism,  in  optics,  is  any  trans- 
parent medium  comprised  between  two  plane  surfaces  inclined  to 


Refraction  by  a  parallel  plate. 


Refraction  through  a  prism. 

each  other.     The  intersection  of  the  two  planes  is  called  the  edge,  and 


LIGHT. 


59 


the  angle  between  them  is  called  the  refracting  angle.      Triangular 
glass  prisms  are  generally  used. 

In  Fig.  19,  ABC  is  a  section  of  a  prism.  A  is  called  the  summit  or 
apex,  and  BC  the  base.  A  ray  of  light,  SI,  falling  upon  the  prism 
will  not  pass  through  it  in  a  straight  line,  SIS',  but  is  bent  out  of  its 
course  twice,  in  accordance  with  the  law  of  refraction,  first  from 
I  to  I',  and  then  to  K.  The  amount  of  bending  depends  on  the 
angle  of  the  prism,  its  material,  and  the  angle  of  incidence  of  the 
ray,  shown  in  i,  while  r  is  the  angle  of  refraction.  The  angle  D 
represents  the  angle  of  deviation. 

Dispersion.  In  Fig.  19,  the  ray  is  represented  by  a  single  line 
throughout.  In  reality,  matters  are  more  complicated,  as  white 
light  is  made  up  of  rays  of  different  colors,  each  of  which  has  a  dif- 
ferent angle  of  refraction.  The  result  is  that  when  a  beam  of  white 
light  falls  on  a  prism  it  does  not  come  through  as  white  light,  but 
the  constituent  colors  are  refracted  at  different  angles,  giving  rise  to  a 
band  of  light  containing  all  the  colors  of  the  rainbow,  viz.,  red, 
orange,  yellow,  green,  blue,  indigo,  violet ;  red  being  less  refracted, 
violet  most.  Such  a  band  of  colors  is  known  as  the  prismatic 
spectrum. 

In  Fig.  20,  A  represents  a  ray  of  light  which  if  unbent  would  strike 
a  screen  at  X,  but  the  prism  P  intervening  the  ray  is  refracted  and 
at  the  same  time  resolved  into  its  constituents,  which  form  the  spec- 
trum, the  colors  of  which  are  indicated  by  the  initial  letters.  This 

FIG.  20. 


Prismatic  spectrum. 


spreading  out  of  light,  and  its  separation  into  different  colors,  are 
called  dispersion. 

The  spectroscope  is  an  instrument  that  serves  for  conveniently 
observing  the   spectrum.     Differently  constructed    instruments  are 


60 


CHEMICAL  PHYSICS. 


employed,  of  which  Fig.  21  represents  the  single-prism  spectroscope, 
which  is  most  largely  used.  It  consists  of  the  prism  P  and  of 
three  telescopes  directed  toward  it.  The  light  is  permitted  to  enter 
the  tube  A  through  a  narrow  slit  at  its  distal  end,  while  at  the 
other  end  a  convex  lens,  called  the  collimator,  serves  to  collect  the 
light  into  nearly  parallel  beams.  These  beams  pass  through  the 
prism  where  the  dispersion  is  brought  about,  and  the  spectrum  thus 
formed  is  observed  at  d  through  the  telescope  B.  Through  the  third 

FIG.  21. 


Spectroscope. 

tube,  C,  a  fine  scale  for  measurement  of  the  relative  position  of  lines 
or  colors  is  reflected  to  the  eye  of  the  observer.  This  scale  is  usually 
photographed  on  glass,  and  when  illuminated  by  a  candle  or  some 
other  stronger  light  the  image  of  the  scale  is  directed  upon  the  face 
of  the  prism  in  such  a  manner  that  it  is  reflected  down  the  axis  of 
the  observing  telescope,  and  is  seen  above  or  below  the  spectrum, 
according  to  the  direction  given  to  the  axis  of  the  scale  tube.  The 
glass  vessel  a  serves  as  a  container  for  a  liquid  to  be  examined  spec- 
troscopically. 

A  second  form  of  spectroscope,  known  as  the  direct-vision  spec- 
troscope, is  shown  in  Fig.  22.  It  consists  of  a  cylindrical  tube 
provided  with  ocular  and  containing  from  three  to  seven  prisms, 


LIGHT.  61 

a  draw-tube  with  adjustable  slit,  and  a  collimator  lens  placed 
between  them  to  render  the  rays  parallel.  The  prisms  placed 
opposite  to  one  another  are  made  of  crown  glass  and  flint  glass,  re- 
spectively. The  dispersive  power  of  the  latter  is  nearly  double  that 
of  crown  glass,  while  the  deviating  powers  of  the  two  glasses  do  not 
differ  much.  The  result 

is  that  a  beam  of  light  Fl°-  22- 

entering  through  the  slit 
undergoes  but  little  de- 
viation from  its  original 

COlirse,    while      there      is  Direct-vision  spectroscope. 

sufficient  dispersion  be- 
tween  its  colors  to  produce  a  spectrum  available  for  spectroscopic 
uses.     When  the  luminous  flame  of  a  candle,  oil,  or  gas  is  examined 
spectroscopically,  it  shows  a  continuous  spectrum — i.  e.,  this  white 
light  has  been  decomposed  into  its  constituents. 

Bright  line  spectra.  If  into  a  non-luminous  flame  of  a  Bunsen 
burner  a  platinum  wire  which  has  been  previously  dipped  into 
common  salt  (sodium  chloride)  be  held,  the  flame  will  be  colored 
yellow,  and  if  it  be  examined  by  the  spectroscope  there  will  be  seen 
a  bright-yellow  line  in  the  yellow  part  of  the  spectrum,  wrhile  no 
other  colors  are  visible.  In  thus  examining  salts  of  other  metals, 
such  as  potassium,  lithium,  calcium,  etc.,  by  holding  in  the  flame  by 
means  of  platinum  wire,  it  will  be  seen  that  each  one  gives  a  number 
of  characteristic  bands  or  lines  in  different  parts  of  the  spectrum,  the 
remaining  portion  being  quite  dark.  So  characteristic  are  these 
spectra  of  different  elements  that  they  furnish  a  distinctive  means 
of  recognition ;  and  indeed  some  elements  have  been  discovered  by 
this  method.  These  spectra  can  be  seen  only  when  the  substance  is 
heated  to  a  point  where  volatilization  takes  place,  because  gases  alone 
show  the  property  of  giving  discontinuous,  or  bright  line,  spectra, 
and  no  two  gases  give  the  same  spectrum. 

The  reason  that  luminous  flames  give  a  continuous  spectrum  is 
that  the  luminosity  is  due  to  light  emitted  by  particles  of  solid  carbon 
floating  in  the  burning  gas.  This  shows  that  the  spectroscope  fur- 
nishes a  reliable  means  of  determining  whether  light  proceeds  from 
a  luminous  solid  or  a  luminous  gas,  as  all  luminous  solids  and  liquids 
give  continuous  spectra. 

Absorption  spectra.  If  the  spectroscope  is  so  arranged  that  a 
continuous  spectrum  is  obtained  from  a  strongly  luminous  flame,  or 


62  CHEMICAL  PHYSICS. 

from  an  electric  light,  and  if  then  a  little  sodium  chloride  be  evapo- 
rated in  the  flame  of  a  Bunsen  burner  that  has  been  placed  between 
the  slit  and  the  luminous  flame,  it  will  be  seen  that  the  spectrum  is 
no  longer  continuous,  but  that  a  black  line  intercepts  it,  a  line  hold- 
ing precisely  the  position  occupied  by  the  yellow  sodium  line  seen 
on  a  dark  background  when  the  luminous  flame  is  removed.  In 
repeating  the  experiment  with  the  salts  of  various  metals,  we  find 
like  conditions,  viz.,  the  discontinuous  bright  color  spectra  of  indi- 
vidual metals  are  converted  into  spectra  showing  black  lines  in  the 
continuous  spectrum  obtained  from  the  luminous  flame.  (See  spectra 
on  plate  facing  title  page. 

From  these  facts  we-  may  draw  the  conclusion  that  the  vapors  of 
different  substances  absorb  precisely  the  same  rays  that  they  are 
capable  of  emitting.  Such  spectra  are  called  absorption  spectra,  or 
reversed  spectra. 

Absorption  spectra  are  also  of  interest  because,  if  white  sunlight 
be  examined  with  a  spectroscope  of  sufficiently  high  power,  it  is  found 
not  to  be  continuous,  but  to  contain  many  hundreds  of  black  lines, 
called  after  their  discoverer  Frauenhofer  lines.  The  more  prominent 
lines  are  designated  by  letters  or  numbers,  as  shown  in  the  solar  spec- 
trum represented  on  the  accompanying  plate.  On  comparing  these 
lines  in  the  sun  spectrum  with  the  positions  of  lines  obtained  by  known 
elements,  such  as  iron,  sodium,  calcium,  etc.,  it  is  found  that  they 
correspond  exactly  to  one  another.  The  explanation  given  is  this  : 
The  main  body  of  the  sun  consists  of  a  highly  luminous  mass  sur- 
rounded by  an  atmosphere  of  cooler  vapor.  The  luminous  body 
would  give  a  continuous  spectrum,  but  the  rays  passing  through  the 
vapors  of  the  sun's  atmosphere  are  partly  absorbed,  and  thus  a  large 
number  of  black  lines  are  produced.  Absorption-spectra  are,  further- 
more, of  great  interest,  because  when  light  passes  through  certain 
liquids,  such  as  blood  or  a  solution  of  quinine  sulphate,  dark  line 
spectra  are  obtained,  sufficiently  characteristic  to  assist  in  the  recog- 
nition of  these  substances. 

From  what  has  been  said,  we  learn  that  we  have  three  kinds  of 
spectra,  viz.,  continuous  spectra,  produced  by  luminous  solids  or 
liquids,  and  possibly  by  luminous  gases  tinder  high  pressure  ;  bright 
line  spectra,  produced  by  luminous  vapors ;  and  absorption  spectra, 
produced  by  light  that  has  passed  through  certain  media. 

The  value  of  the  spectroscope  depends  on  the  use  made  of  it  in 
spectroscopic  analysis,  as  both  the  bright  line  spectra  and  absorption 
spectra  enable  us  to  determine  the  nature  of  many  substances,  and 


LIGHT.  63 

to  differentiate  between  elements  present  not  only  on  our  globe,  but 
in  other  celestial  bodies  likewise. 


Double  refraction.  A  plate  of  glass  will  not  interfere  with  read- 
ing printed  matter  over  which  the  plate  is  laid.  But  in  trying  to 
read  through  several  varieties  of  transparent  crystalline  substances  a 

FIG.  23. 


Double  refraction. 


peculiar  phenomenon  is  noticed ;  as  then  each  letter  will  be  dupli- 
cated, as  shown  in  Fig.  23,  where  a  piece  of  Iceland  spar  (crystallized 
calcium  carbonate)  is  placed  over  reading  matter. 

If  a  pinhole  be  made  through  a  card,  and  the  card  be  placed  over  a 
crystal  of  Iceland  spar  and  held  before  the  eye  toward  the  light,  there 
will  appear  to  be  two  holes,  with  light  shining  through  each.  If 
the  crystal  be  made  to  rotate  in  a  plane  parallel  with  the  card,  then 
one  of  the  holes  will  appear  to  remain  nearly  at  rest,  while  the 
other  rotates  about  it.  These  facts  show  that  a  ray  of  light  on  enter- 
ing the  crystal  is  divided  into  two  parts,  one  of  which  obeys  the 
law  of  regular  refraction,  and  is  called  the  ordinary  ray,  while  the 
other,  which  does  not,  is  termed  the  extraordinary  ray.  This  power 
of  certain  substances  to  refract  light  rays  in  two  directions  is  known 
as  double  refraction.  . 

In  all  crystals  which  produce  double  refraction  there  is  one  direc- 
tion (in  some  even  two  directions)  in  which  an  object,  looked  at 
through  the  crystal,  does  not  appear  double.  The  line  through 
which  double  refraction  is  suspended  is  called  the  optic  qxis,  and  is  a 
line  around  which  the  molecules  appear  to  be  arranged  symmetrically. 

Polarization.  The  semitransparent  mineral  tourmaline  is  another 
substance  refracting  double.  Two  rays,  the  ordinary  and  the  ex- 
traordinary, are  formed  when  a  ray  of  light  is  passed  through  a  plate 


64 


CHEMICAL  PHYSICS. 


of  this  substance,  just  as  in  the  case  of  Iceland  spar;  but  tourmaline 
possesses  the  peculiar  property  of  absorbing  the  ordinary  ray,  while 
the  extraordinary  one  passes  through. 

If  two  plates,  cut  parallel  to  the  axis  of  the  crystal,  are  laid  upon 
each  other  in  a  crossed  position,  as  AB  in  Fig.  24,  it  is  found  that 


FIG.  24. 


Tourmaline  plates. 

light  from  the  first  plate  is  cut  off  by  the  second  one,  and  darkness 
results.  If  one  plate  be  turned  round  upon  the  other,  it  will  be 
found  that  the  combination  is  most  transparent  in  two  positions  dif- 
fering by  180  degrees,  one  of  them,  ab,  being  the  natural  position 
which  the  plates  originally  occupied  in  the  crystal.  The  combina- 
tion is  most  opaque  in  the  two  positions  at  right  angles  with  these, 
while  intermediate  positions,  such  as  a'b',  show  intermediate  be- 
havior. These  facts  show  that  light  which  has  passed  through  one 
such  plate  is  in  a  peculiar  condition.  It  is  said  to  be  plane-polarized. 
In  order  to  understand  polarization  of  light,  we  should  bear  in 
mind  that  the  particles  of  ether  undulate  in  a  variety  of  planes  per- 
pendicular to  the  line  of  propagation.  We  assume  that  in  polarized 
light  the  undulations  of  the  ether  particles  take  place  in  a  single 
plane.  These  ether  undulations  may  be  compared  to  those  taking 
place  in  a  cord  fastened  at  one  end  and  shaken  by  the  hand  at  the 

FIG.  25. 


Undulation  in  a  cord. 


other  end,  as  in  Fig.  25.  According  to  whether  we  move  the  hand 
horizontally,  obliquely,  or  vertically,  the  undulations  will  lie  in  a 
horizontal,  oblique,  or  vertical  plane,  as  represented  at  A. 


LIGHT.  65 

If  a  cardboard,  with  a  long  slit  in  it,  be  held  over  the  string, 
the  string  will  vibrate  in  one  plane  only,  viz.,  in  that  of  the  slit. 
Instead  of  one  cardboard,  two  or  more  may  be  used,  and  as  long  as 
the  slits  are  in  one  plane  the  vibrations  will  proceed  in  that  plane. 
If,  however,  the  slit  of  one  card  be  set  at  a  right  angle  to  that  of 
another  card  placed  over  the  string,  then  vibrations  will  no  longer 
be  propagated. 

To  make  the  action  of  the  tourmaline  plates  still  more  intelligible, 
we  may  compare  it  to  that  of  a  grating,  A,  Fig.  26,  formed  of  parallel 
vertical  rods  which  permit  the  passage  of  all  vertical  planes,  as 
aa,  but  intercept  that  of  horizontal  planes,  cc.  As  long  as  the  rods 


FIG.  26. 
A 

GH 

a 

.,,11111 

Explanatory  diagram  of  the  action  of  tourmaline  plates. 

of  the  gratings  A  and  B  are  in  the  same  plane,  a  string  may  be 
made  to  vibrate  through  these  gratings  parallel  to  the  rods,  but  when 
set  at  a  right  angle  this  becomes  impossible. 

When  a  ray  of  light  strikes  a  plate  of  tourmaline  it  permits  the 
passage  of  those  undulations  which  are  parallel  with  its  axis,  but  it 
absorbs  those  undulations  which  are  in  planes  at  right  angles  to  its 
axis.  The  rays  which  pass  through  the  plate  produce  the  polarized 
light. 

Polariscope.  As  the  unaided  eye  cannot  differentiate  between 
common  and  polarized  light,  instruments  are  constructed  by  which 
the  phenomena  of  polarization  can  be  studied,  and  these  instruments 
are  known  as  polariscopes,  polarimeters,  or,  in  a  special  case,  sac- 
clmrimeters.  They  all  contain  some  substance,  known  as  a  polarizer, 
such  as  tourmaline,  Iceland  spar,  etc.,  serving  as  a  polarizer  of  light ; 
and  a  second  substance,  called  an  analyzer,  for  the  detection  of  that 
light.  In  the  above  experiment  with  tourmaline  plates  the  first 
plate  serves  as  a  polarizer  and  the  second  as  an  analyzer. 

The  material  used  generally  for  polarization  is  Iceland  spar,  as  it 
is  more  transparent  than  tourmaline.  Instead  of  using  plates  of 
this  material,  prisms,  known  as  NicoVs  prisms,  are  made  by  sawing 

5 


66  CHEMICAL  PHYSICS. 

through  a  crystal  from  one  obtuse  angle  to   the   other.     The   two 

parts,  after  their  surfaces  have 
been  well  polished,  are  joined 
by  a  transparent  cement  of 
Canada  balsam.  Fig.  27  rep- 
resents a  section  of  this  prism. 
DB  indicates  the  line  where  the 
crystal  has  been  cut  and  ce- 
mented. A  ray  of  light  passing 

Nicol's  prism.  fr°m  the  °bJect  tO  thf  side  AD 

is  doubly  refracted  in  such  a 

manner  that  the  ordinary  ray  on  striking  the  balsam  is  totally  re- 
flected to  the  side  AB,  and  there  refracted  out  of  the  crystal,  while 
the  extraordinary  ray  passes  on  and  emerges  at  the  side  BC  as  a 
polarized  ray.  If  this  ray  is  now  passed  into  a  second  NicoPs  prism 
parallel  to  the  first,  as  if  it  were  a  continuation  of  the  latter,  it  will 
pass  through  unchanged.  If  the  second  prism  be  turned  through  an 
angle  of  90  degrees — that  is,  if  the  two  prisms  be  crossed — the  ray  of 
light  will  be  cut  off  entirely.  The  ray  in  the  second  prism  becomes 
an  ordinary  one,  and  is  totally  reflected  at  the  layer  of  balsam 
through  the  side  of  the  prism  and  is  lost,  as  in  the  case  of  the  first 
prism.  In  intermediate  positions  between  the  crossed  and  the  parallel 
ones  the  extraordinary  ray  from  the  first  prism  is  decomposed  in  the 
second  one  partly  into  an  ordinary  and  partly  into  an  extraordinary 
ray.  The  former  is  reflected  out  of  the  prism,  while  the  latter  goes 
through,  so  that  more  and  more  light  will  pass  through  as  the  second 
prism  is  turned  so  as  to  approach  parallelism  to  the  first.  Thus  it  is 
easily  seen  that  a  Nicol  prism  may  serve  not  only  to  produce  polar- 
ized light,  but  also  to  detect  such  light. 

Polarized  light  is  extensively  used  in  the  examination  of  minerals 
and  salts,  as  thin  slices  of  crystals  belonging  to  different  crystallo- 
graphic  systems  when  brought  between  two  NicoPs  prisms  show 
rings  or  bands  of  colors  characteristic  of  the  respective  systems. 

Many  organic  liquids  and  solids  in  solution  have  a  peculiar  action 
on  polarized  light.  Such  substances,  for  example,  are  sugars,  tar- 
taric  acid,  alkaloids,  essential  oils,  etc.  If  two  NicoPs  prisms  are 
crossed  so  that  no  light  is  emitted,  and  a  solution  of  sugar,  for  ex- 
ample, is  placed  in  a  glass  tube  between  the  prisms,  light  will  pass. 
The  sugar  turns  the  direction  of  vibrations  of  the  light  as  it  comes 
from  the  first  prism,  and  the  effect  is  the  same  as  if  the  second  prism 
had  been  turned  with  respect  to  the  first  one  as  described  above, 


LIGHT.  67 

where  nothing  intervened  between  the  prisms.  Substances  which 
have  such  an  effect  on  polarized  light  are  said  to  turn  the  plane  of 
polarization,  and  are  called  optically  active.  The  amount  of  this 
turning  or  rotation  of  the  plane  of  polarization  can  be  measured  by 
noting  to  what  extent  the  second  prism  must  be  turned  to  the  right 
or  left  to  produce  the  original  condition,  namely,  darkness. 

Substances  which  act  in  such  a  manner  that  the  analyzer  must  be 
turned  to  the  right  to  produce  darkness  are  called  dextrorotatory,  or 
right-handed;  while  those  substances  acting  in  the  opposite  manner 
are  called  levorotatory ,  or  left-handed.  Substances  acting  in  neither 
way  are  called  optically  inactive. 

The  degree  of  rotation  varies  with  the  quantity  of  substance  in 
solution  for  a  definite  length  of  a  column  of  the  latter,  and  hence  is 
used  to  determine  the  percentage  strength,  for  example,  that  of  sugar 
in  urine  and  other  liquids.  Polariscopes  are  therefore  valuable  quan- 
titative analytical  instruments. 

All  polariscopes  consist  essentially  of  a  polarizer  and  an  analyzer, 
with  a  tube  between  them  for  containing  the  substance  to  be  exam- 
ined, and  a  scale  for  reading  the  amount  of  rotation  produced,  all 
carried  on  a  suitable  metallic  support.  In  addition  to  these  essential 
parts,  the  polariscopes  of  different  makers  are  provided  with  numer- 
ous contrivances  rendering  the  instruments  more  perfect  and  the 
analytical  results  obtained  more  accurate. 

Plates  of  crystalline  substances,  as  quartz,  have  a  noteworthy 
effect  when  placed  in  the  path  of  polarized  light  between  a  polarizer 
and  an  analyzer.  Not  only  do  they  prevent  the  light  from  being 
entirely  shut  off  when  the  Nicol  prisms  are  crossed,  but  they  produce 
sharply  defined  appearances,  as  color  tints,  alternate  lines  of  light 
and  darkness,  equal  or  unequal  illumination  of  the  two  halves  of 
the  field  of  view,  etc.  The  appearances  depend  on  the  particular 
arrangement  and  direction  of  cutting  of  the  crystalline  plates.  A 
full  explanation  of  the  cause  of  these  effects  is  beyond  the  scope  of 
this  work. 

Fig.  28  shows  Lippich's  polariscope,  used  chiefly  for  sugar  solu- 
tions. The  optical  arrangement  is  shown  above  the  drawing  of  the 
instrument,  and  consists  of  a  telescope,  a-a,  the  analyzer  6,  a  station- 
ary polarizer,  c,  a  movable  polarizer,  d,  and  the  condensing  lens  e ; 
/represents  a  number  of  diaphragms.  The  liquid  to  be  examined  is 
placed  in  the  tube,  and  the  rotatory  power  of  the  substance  is  deter- 
mined by  turning  the  polarizer  to  the  right  or  left,  as  the  case  may 
require.  The  amount  of  turning  necessary  to  establish  the  same  con- 


68 


CHEMICAL   PHYSICS. 


ditions  existing  before  the  optically  active  substance  was  brought 
between  the  prisms  is  read  off  on  the  movable  disk,  which  is  pro- 


FIG.  28. 


a    b  f 


fe  dfe 


Lippich's  polariscope. 

vided  with  a  scale.     A  lamp  supplies  the  illumination   by  means  of 
a  flame  colored  yellow  by  sodium. 

Chemical  effects  of  light.  The  well-known  bleaching  effect  that 
sunlight  has  on  many  dye-stuffs  shows  that  light  has  the  power  to 
bring  about  chemical  changes.  The  art  of  photography  is  one  of 
the  practical  applications  of  this  principle.  Plant-life  is  dependent 
on  the  light  that  reaches  us  from  the  sun.  The  storage  of  many 
chemicals  in  the  dark,  or  in  colored  glass  bottles,  is  often  necessary  to 
protect  them  from  the  decomposing  influence  of  light. 

QUESTIONS. — What  are  our  views  regarding  the  nature  and  propagation  of 
light?  Explain  reflection,  refraction,  and  dispersion  of  light.  What  is  the 
prismatic  spectrum,  and  how  is  it  obtained  ?  Give  a  full  explanation  of  the 
spectroscope  and  of  its  use  in  chemical  analysis.  Define  continuous,  bright- 
line,  and  absorption-spectra,  and  state  the  conditions  under  which  they  are 
formed.  What  is  meant  by  double  refraction  and  by  polarization  of  light? 
Mention  the  essential  parts  of  the  polariscope,  and  the  use  made  of  it  in  chem- 
ical analysis.  How  are  the  different  colors  produced  under  the  influence  of 
white  light?  What  is  revealed  to  us  by  the  Frauenhofer  lines  in  the  solar 
spectrum?  Explain  the  terms  dextrorotatory,  levorotatory,  and  optically 
inactive  substances. 


ELECTRICITY.  69 

4.  ELECTRICITY. 

Electricity  generated  by  friction.  When  a  glass  tube  is  rubbed 
with  a  piece  of  silk,  it  will  be  found  to  have  acquired  the  property 
of  attracting  light  bodies,  such  as  scraps  of  paper,  sawdust,  etc. 
Moreover,  if  the  tube  be  brought  close  to  the  face,  a  sensation  similar 
to  that  produced  by  the  contact  of  a  cobweb  will  be  experienced. 
If  a  knuckle  be  held  near  the  tube,  a  peculiar  noise  is  heard,  and 
a  spark  may  be  seen  to  pass  between  the  tube  and  the  knuckle. 

These  phenomena  show  that  the  tube  has  acquired  peculiar 
properties  by  friction.  It  is  said  to  be  electrified,  and  the  name 
electricity  is  given  to  the  cause  producing  these  phenomena.  The 
term  electricity  is  derived  from  the  Greek  electron,  amber,  in  which 
substance  the  property  of  attracting  light  objects  after  the  applica- 
tion of  friction  was  first  noticed  about  twenty-five  hundred  years  ago. 

Conductors  and  non-conductors.  Besides  glass  and  amber, 
there  are  many  substances,  such  as  sulphur,  sealing-wax,  hard 
rubber,  etc.,  which  can  be  readily  electrified  by  friction.  On  the 
other  hand,  a  bar  of  metal  cannot  be  electrified  unless  it  be  fitted  to 
a  glass  rod,  a  piece  of  rubber,  or  to  certain  other  substances,  and 
held  by  this  handle  while  being  rubbed  with  flannel.  .  Moreover,  it 
can  be  shown  that  a  piece  of  glass  or  sulphur  will  attract  particles 
— i.  c.,  becomes  electrified — at  that  spot  only  where  it  has  been  rubbed, 
while  a  tube  of  metal,  fastened  to  a  suitable  handle,  becomes  elec- 
trified over  the  whole  surface  of  the  tube.  These  facts  show  that 
electricity  when  generated  in  such  bodies  as  glass,  sulphur,  and 
rubber,  remains  where  it  has  been  produced,  while  in  metals  it 
immediately  spreads  over  the  whole  mass. 

Bodies  of  the  first  kind,  such  as  glass,  etc.,  are  said  to  be  non-con- 
ductors, while  materials  such  as  metals  are  said  to  be  conductors.  A 
non7conductor  is  often  called  an  insulator,  and  a  conductor  supported 
by  a  non-conductor  is  said  to  be  insulated. 

The  reason  that  conductors,  such  as  metals,  cannot  be  electrified 
by  friction  unless  held  by  a  non-conductor,  is  that  the  human  body  is 
a  good  conductor,  and  therefore  carries  off  the  electricity  as  quickly 
as  it  is  generated. 

No  substance  is  absolutely  non-conducting,  but  the  difference  in 
this  power  possessed  by  what  are  termed  good  conductors  and  non- 
conductors is  very  great.  Of  conductors,  may  be  mentioned  :  All 
metals,  charcoal,  acids,  saline  solutions,  living  animals  and  vege- 


70  CHEMICAL  PHYSICS. 

tables,  water,  moist  earth  and  stones.  Non-conductors  are  :  Shellac, 
rubber,  resins,  sulphur,  wax,  glass,  silk,  wool,  porcelain,  dry  paper 
and  dry  air. 

Duality  of  electricity.  For  a  further  study  of  electrical  phe- 
nomena the  simple  instrument  known  as  the  electric  pendulum  or 
pith -ball  electroscope  may  be  used.  It  consists  of  a  pith-ball  sus- 
pended by  a  silk  fibre  from  an  insulated  support.  When  an  electri- 
fied glass  rod  is  brought  near  the  ball,  the  latter  is  attracted ;  but 
as  soon  as  it  touches  the  rod  the  attraction  is  changed  to  repulsion, 
which  lasts  as  long  as  the  ball  retains  the  electricity  it  has  acquired 
by  contact.  The  same  phenomena  may  be  shown  by  employing  any 
other  electrified  body,  for  example  a  piece  of  sealing-wax,  sulphur, 
etc.,  in  place  of  the  glass  rod.  If  while  the  pith-ball  exhibits  re- 
pulsion for  the  glass  electrified  resin  is  brought  near  the  ball,  it  is 
attracted  by  the  resin ;  and  when  it  is  repelled  by  the  resin  it  is 
attracted  by  the  glass.  These  phenomena  clearly  show  that  the 
electricity  developed  on  the  resin  is  not  of  the  same  kind  as  that 
developed  on  the  glass.  They  exhibit  opposite  forces  toward  any 
third  electrified  body,  each  attracting  what  the  other  repels.  They 
have  accordingly  received  names  which  indicate  opposition.  The 
electricity  which  glass  acquires  when  rubbed  with  silk  is  called  vitre- 
ous or  positive,  and  that  which  resin  acquires  by  friction  with  flannel, 
resinous  or  negative  electricity. 

On  repeating  the  experiment  with  other  substances,  it  is  found 
that  all  electrified  bodies  behave  like  either  glass  or  resin.  An  elec- 
trified body  is  spoken  of  as  being  charged  with  electricity ;  the 
charge  may  be  either  positive  or  negative.  Experiments  show 
that,  whenever  electricity  of  one  kind  is  developed,  whether  by 
friction  or  other  means,  an  equal  quantity  of  the  opposite  kind  is 
simultaneously  developed.  Thus,  in  rubbing  glass  and  silk  the  glass 
is  charged  with  positive,  the  silk  with  negative  electricity.  If  a 
conductor  receives  two  charges  of  electricity  of  equal  quantity  but 
opposite  kind,  it  exhibits  no  trace  of  electricity,  the  two  charges 
having  neutralized  one  another. 

The  kind  of  electricity  which  a  body  obtains  by  friction  with 
another  body  evidently  depends  on  the  nature  of  the  bodies.  For 
instance,  if  glass  be  rubbed  with  cat's  skin  the  glass  becomes  charged 
with  negative,  but  if  rubbed  with  silk  it  becomes  charged  with  posi- 
tive electricity.  In  the  following  "  potential  series  "  any  one  of  the 
bodies  named  becomes  positively  electrified  when  rubbed  with  one 


ELECTRICITY.  71 

of  the  bodies  following,  but  negatively  electrified  when  rubbed  with 
one  of  those  which  precede  it : 

1.  Cat's  skin.  5.  Silk.  9.  Sealing-wax. 

2.  Flannel.  6.  Human  body.  10.  Resin. 

3.  Ivory.  7.  Wool.  11.  Sulphur. 

4.  Glass.  8.  Metals.  12.  Gutta-percha. 

When  an  electrified  body  is  brought  to  its  normal  condition  it  is 
said  to  be  discharged.  The  discharge  may  take  place  slowly  through 
the  air,  or  rapidly  by  bringing  the  charged  body  in  contact  with  the 
earth  directly  or  by  means  of  a  conductor,  such  as  the  human  body 
or  a  piece  of  wire.  The  discharge  may  be  accompanied  by  a  flash  of 
light,  called  a  spark. 

Induction.  A  body  charged  with  electricity  will  exert  an  influ- 
ence upon  surrounding  unelectrified  bodies  and  destroy  the  neutral 
condition  existing  in  them,  attracting  to  the  surface  next  to  the  elec- 
trified body  a  charge  the  opposite  to  that  which  it  contains.  But 
while  one  kind  of  electricity  is  drawn  toward  the  original  electrified 
body,  an  equal  quantity  of  the  opposite  kind  of  electricity  is  driven 
toward  the  farther  extremity  of  the  bodies  which  are  under  the  influ- 
ence of  the  electrified  body.  This  action  exerted  by  an  electrified 
body  on  another  body  is  called  induction. 

Induction  of  bodies  connected  with  the  earth  can  last  only  so  long 
as  they  are  under  the  influence  of  the  electrified  body,  because  as 
soon  as  this  is  removed  the  induced  electricity  is  immediately  carried 
off  by  the  earth.  But  if  an  insulated  body  be  brought  near  one  that 
is  electrified,  and  while  under  its  influence  be  touched  at  the  end 
opposite  to  the  electrified  body  so  as  to  carry  off  the  electricity  there 
gathered,  then  on  removing  the  electrified  body  the  previously  neu- 
tral body  will  be  found  to  be  electrified  with  a  charge  opposite  in 
character  to  that  of  the  originally  electrified  body.  This  method  of 
imparting  electricity  is  called  charging  by  induction.  Induction 
furnishes  us  the  explanation  of  the  attraction  and  repulsion  of  light 
materials  by  electrified  bodies.  A  positively  excited  body  decdm- 
poses  the  normal  charge  present  in  other  bodies,  and  if  sufficiently 
light  they  move  toward  the  excited  body,  discharging  their  negative 
electricity  and  becoming  charged  positively  through  contact;  they 
are  now  repelled,  as  both  bodies  are  electrified  alike. 

Electrical  machines.  Electricity  produced  by  friction  or  by 
induction  is  called  static  electricity,  or  electricity  at  rest,  to  differ- 


72  CHEMICAL  PHYSTCS. 

cntiate  it  from  current  electricity,  or  electricity  in  motion,  which  will 
be  considered  later.  Various  machines  have  been  constructed  to 
generate  static  electricity.  In  the  older  forms  of  such  machines 
friction  between  glass  plates  or  glass  cylinders  and  pads  of  silk  served 
as  the  generating  source.  In  the  newer  and  more  powerful  forms 
of  static  machines,  such  as  the  Toepler-Holtz  machines,  induction 
chiefly  is  used  to  generate  the  electricity. 

Nature  of  Electricity. — The  most  modern  theory  of  the  nature  of  elec- 
tricity teaches  that  it  is  a  manifestation  of  some  manner  of  strain  set  up  in  the 
hypothetical  ether.  But  this  theory  cannot  be  discussed  to  advantage  in  this 
volume.  However,  the  following  lines  may  assist  the  student  in  getting  an 
idea  of  what  electricity  is,  and  how  it  acts. 

It  has  been  stated  that  energy  is  a  universal  property  of  matter,  and  that 
energy,  like  matter,  can  neither  be  created  nor  destroyed.  But  energy,  like 
matter,  can  be  changed  from  one  form  .to  another,  or  from  one  place  to 
another.  According  to  whether  energy  manifests  itself  in  masses,  in  mole- 
cules, or  in  atoms,  we  speak  of  mass  energy,  molecular  energy,  and  atomic 
energy.  Mass  energy  becomes  manifest  in  the  attractions  due  to  gravitation, 
such  as  the  fall  of  bodies;  in  magnetic  attractions,  as  when  a  magnet  attracts 
iron  ;  in  electric  attractions,  as  when  an  electrified  body  attracts  light  particles 
of  matter.  Molecular  energy  manifests  itself  in  heat,  in  light,  in  magnetism, 
and  in  electricity.  Just  what  the  difference  is  between  the  different  kinds  of 
molecular  motion  that  produce  in  one  case  heat,  in  others  light  or  electricity, 
has  never  been  discovered.  It  is  supposed  to  be  in  the  form  of  undulations 
or  vibrations,  the  heat  undulations  having  one  form,  the  electric  undulations 
another  form,  so  that  while  both  kinds  of  motion  are  found  in  the  same  body 
at  the  same  time,  they  do  not  interfere  with  each  other. 

Exactly  as  in  the  case  of  heat  and  light,  we  have  to  assume  that  the  propa- 
gation of  electricity  through  space  takes  place  in  the  ether.  There  is,  more- 
over, a  mutual  reaction  between  the  vibratory  motion  of  the  molecules  and  the 
undulatory  motion  of  the  ether,  the  vibrations  producing  the  undulations,  and 
the  undulations,  in  turn,  producing  the  vibrations;  just  as  the  vibratory  strokes 
of  an  oar  produce  waves,  which  in  turn  may  produce  vibrations  in  other  oars 
resting  in  the  water. 

The  conclusion,  therefore,  to  which  we  come  in  regard  to  the  nature  of  elec- 
tricity is  this :  Electricity  is  a  manifestation  of  energy  believed  to  consist  in 
undulations  of  the  ether  and  vibrations  of  the  grosser  molecules  of  matter. 

We  see,  then,  that  electricity  is  neither  energy  nor  matter,  but,  like  heat, 
light,  and  sound,  it  is  an  effect  produced  by  energy  on  matter.  But  as  the 
effect  cannot  be  separated  from  its  cause,  it  is  convenient  to  speak  of  it  as 
electric  energy,  in  the  same  sense  as  we  speak  of  mechanical  enegy,  vital  energy, 
heat  energy,  or  energy  in  any  other  form  in  which  it  becomes  manifest  as  asso- 
ciated with  matter. 

To  obtain  electricity,  energy  in  some  other  form  must  be  expended,  whether 
it  be  the  energy  of  our  body  expended  in  rubbing  together  pieces  of  glass  and 
silk,  or  the  energy  of  chemical  action,  as  in  a  battery  cell,  or  the  potential 


ELECTRICITY.  73 

energy  of  coal  used  in  the  mechanical  working  of  a  dynamo.  All  methods  of 
generating  electricity  bring  about  a  disturbance  of  the  electrical  equilibrium 
existing  under  normal  conditions  in  ail  matter.  Whenever  this  equilibrium  is 
disturbed  there  is  a  tendency  to  re-establish  it,  and  it  is  during  the  process  of 
re-establishing  the  equilibrium  that  work  is  done  electrically. 

One  of  the  principal  reasons  that  electrical  phenomena  offered  great  diffi- 
culties to  the  investigator  is  that  the  electric  undulations  taking  place  in  the 
ether  produce  no  effect  whatever  on  our  senses.  Waves  of  air  in  striking  certain 
nerves  in  the  ear  produce  the  sensation  of  sound ;  waves  of  ether  affect  certain 
other  nerves  in  such  a  manner  as  to  produce  the  sensations  of  heat  and  light, 
but  man  has  no  nerves  that  are  affected  by  electric  or  magnetic  waves — i.  e., 
he  is  magnetically  and  electrically  blind  and  deaf.  The  slow  development  of  the 
science  of  electricity  was  due  to  this  fact. 

Magnetism.  The  native  iron  ore  known  as  lodestone  or  mag- 
netite (ferrous  ferric  oxide)  has  the  power  of  attracting  bits  of  steel 
or  iron,  and  also  possesses  the  property  of  pointing  north  and  south 
when  suspended  by  a  thread.  Pieces  of  iron  may  be  caused  to 
acquire  the  same  properties,  and  all  bodies  possessing  them  are  called 
magnets,  while  magnetism  is  the  term  used  to  designate  the  magnetic 
condition  of  matter. 

Any  bar  of  steel  or  iron  may  be  magnetized  by  drawing  over  it 
lengthwise  a  magnet ;  but  while  a  piece  of  hard  steel  will  remain 
a  magnet  almost  indefinitely,  soft  iron  loses  its  magnetism  very 
readily.  A  pivoted  or  suspended  magnet  always  places  itself  in  the 
direction  of  the  " magnetic  meridian'7  of  the  earth — i.e.,  nearly 
north  and  south.  The  end  of  the  magnet  pointing  north  is  called 
its  north  pole,  the  other  its  south  pole.  On  bringing  one  pole  of  a 
magnet  near  a  suspended  magnet  it  is  found  that  with  magnetism,  as 
with  electricity,  like  poles  repel  and  unlike  poles  attract  each  other. 
There  exists  also  magnetic  induction,  corresponding  to  induction  by 
electricity.  This  can  be  shown  by  placing  a  bar  of  iron  near  a 
magnet,  when  it  is  found  that  the  end  of  the  bar  nearest  the  north 
pole  is  converted  into  a  south  pole,  and  vice  versa. 


When  a  magnetized  bar  is  dipped  into  iron  filings,  masses  of  the  filings  adhere 
to  the  two  extremities — i.  e.,  to  the  two  poles — while  none  are  found  at  the 
centre.  When  a  magnetic  bar  is  cut  in  halves  at  the  non-magnetic  centre, 
two  magnets  are  produced ;  and  this  cutting  into  smaller  lengths  may  be  con- 
tinned  indefinitely,  with  the  result  that  each  length,  and  finally  each  particle, 
possesses  two  poles  and  an  intermediate  neutral  zone.  This  fact,  as  well  as 
other  considerations,  has  led  to  the  assumption  that  each  molecule  of  iron  is 
a  magnet  in  itself.  In  ordinary  iron  these  little  magnets  are  not  arranged 
systematically,  while  in  magnetized  iron  all  the  north  poles  point  in  one  direc- 
tion, all  the  south  poles  in  the  opposite  direction.  Moreover,  it  is  supposed 


74  CHEMICAL  PHYSICS. 

that  each  magnetic  molecule  is  traversed  by  a  closed  electric  circuit,  which 
currents  become  parallel  upon  magnetization  of  ordinary  iron.  According  to 
this  theory,  magnetism  is  a  manifestation  of  electrical  energy. 

The  shape  given  to  magnets  is  usually  that  of  a  bar  or  of  a  horse- 
shoe. A  bar  of  soft  iron  laid  over  the  poles  of  a  horseshoe  magnet 
is  called  an  armature;  it  serves  to  retain  the  full  power  of  the 
magnet. 

When  fine  iron  filings  are  sprinkled  on  a  piece  of  glass  or  card- 
board which  has  been  placed  over  a  magnet,  the  filings  arrange 
themselves  in  lines  radiating  from  either  pole,  forming  graceful 
curves  from  pole  to  pole.  These  lines,  called  lines  of  magnetic  force, 
represent  the  resultant  of  the  combined  action  of  the  two  poles,  the 
space  surrounding  a  magnet  as  far  as  its  influence  extends  being 
termed  its  magnetic  field.  A  magnetic  needle  placed  anywhere  in 
this  field  follows  the  lines  of  magnetic  force,  always  assuming  a 
position  tangent  to  the  magnetic  curve. 

The  explanation  given  for  the  fact  that  the  magnetic  needle  points 
north  and  south  is  that  the  earth  itself  is  an  immense  magnet,  pos- 
sessing two  magnetic  poles  which  are  close  to  the  geographical  poles. 

Electricity  generated  by  chemical  action.  On  placing  a  strip 
of  ordinary  zinc  in  diluted  sulphuric  acid,  bubbles  of  hydrogen  gas 
are  evolved  on  its  surface  and  the  zinc  gradually  dissolves ;  a  piece 
of  platinum  placed  in  the  acid  is  not  affected  at  all.  If,  however, 
strips  of  zinc  and  platinum  are  placed  in  a  vessel  containing  diluted 
acid,  on  connecting  the  plates  above  the  liquid  by  a  conductor, 
for  instance  by  a  piece  of  copper  wire,  characteristic  changes  take 
place.  First,  the  evolution  of  gas  stops  on  the  zinc,  while  bubbles 
of  hydrogen  escape  from  the  surface  of  the  platinum.  Next,  on 
placing  the  connecting  wire  near  a  magnetic  needle,  this  is  turned 
from  its  course — i.  e.,  deflected.  And  again,  on  cutting  the  wire  and 
placing  the  tongue  between  the  two  ends,  a  metallic  taste  and  a 
tingling  sensation  are  perceived.  All  these  phenomena  cease  as  soon 
as  the  connection  between  the  plates  is  broken,  and  reappear  when 
connection  is  again  established. 

Undoubtedly  something  takes  place  in  the  wire  while  the  plates 
are  in  the  diluted  acid.  Further  investigation  shows  that  during 
the  action  of  the  acid  on  the  metals  electricity  is  generated,  which 
travels  through  the  wire,  imparting  to  it  characteristic  properties. 

Galvanic  or  voltaic  cells.     In  place  of  zinc,  platinum,  and  sul- 


ELECTRICITY.  75 

phuric  acid,  many  other  materials  may  be  used  to  bring  about  the 

conditions  described  in  the  preceding  paragraph  ;  indeed,  electricity 

is  generated  whenever  two  solids  (plates  or  cylinders  are  generally 

used),   conductors  themselves  and    connected   by  a  conductor,  are 

placed  in  a  liquid  that  has  the  power  to  act  chemically  on  one  of  the 

solids.    Any  such  arrangement  is  termed 

a  galvanic  or  voltaic  cell.     Here  chemical  FIG.  29. 

action  causes  the  generation  of  electricity, 

resulting  in  the  zinc-platinum  cell  in  the 

splitting  up  of  sulphuric  acid,  H2SO4, 

the   hydrogen,    H2,   escaping   from    the 

platinum    plate,    while  the    group   SO4 

combines   with    the  zinc,   forming   zinc 

sulphate,  ZnSO4,  which  dissolves  in  the 

water. 

Many  combinations  are  employed  in 
the  different  cells  for  generating  elec- 
tricity.    Fig.  29  represents  the  Daniell  Danieii's  ceil. 
cell.     It  consists  of  the  glass  jar  S,  con- 
taining a  saturated  solution  of  cupric  sulphate,  in  which  stands  the 
copper  cylinder  C.     Inside  of  this  cylinder  fits  a  porous  cell,  A,  con- 
taining sulphuric  acid,  and  into  this  dips  the  zinc  plate. Z. 

Chemically  pure  zinc  is  scarcely  acted  on  by  diluted  sulphuric  acid  ;  ordi- 
nary zinc  contains  metallic  impurities,  and  as  these  are  in  contact  with  zinc, 
they  set  up  a  galvanic  action,  and  thus  bring  about  the  chemical  changes  above 
described. 

What  is  believed  to  take  place  in  any  galvanic  cell  is  that  the 
electrolytic  fluid — i.  e.,  the  active  agent  in  the  liquid  state — is  split 
up  into  two  component  parts,  called  ions,  and  that  these  ions,  charged 
with  positive  and  negative  electricity,  respectively,  unload  these 
charges  on  the  two  plates,  while  an  equalizing  effect  is  brought  about 
through  the  connecting  wire.  In  other  words,  there  is  a  constant 
disturbance  of  the  electrical  equilibrium  through  chemical  action, 
and  a  tendency  to  re-establish  the  equilibrium,  which  tendency  pro- 
duces the  current. 

One  of  the  plates  (platinum,  in  the  case  cited  above)  is  known 
as  the  positive  electrode  or  anode,  while  the  other  one  (zinc)  is  the 
negative  electrode  or  cathode  of  the  cell.  The  same  terms  are  used 
also  to  designate  the  terminals  of  the  wires  leading  from  the  two 
plates,  which  terminals  are  called  also  +  and  —  poles. 


76  CHEMICAL  PHYSICS. 

Whenever  the  plates  are  connected  by  the  conducting  wire  elec- 
tricity passes  from  the  anode  through  the  wire  to  the  cathode,  and 
through  the  liquid  back  to  its  point  of  origin.  This  continuous 
motion  is  called  the  electric  current,  and  the  different  parts  through 
which  the  current  passes  are  known  as  the  circuit.  Whenever  the 
connection  is  broken  at  any  point  the  circuit  is  said  to  be  open  ; 
otherwise  it  is  closed.  If  the  circuit  be  open,  both  plates  become 
charged  with  positive  and  negative  electricity,  respectively ;  but  as 
there  is  no  conductor  to  carry  off  these  charges,  further  accumulation 
stops,  and  chemical  action  ceases  until  the  circuit  is  again  closed. 

Whenever  two  or  more  galvanic  cells  are  connected  so  as  to  use  in 
one  circuit  the  electricity  generated  by  all  the  cells,  the  arrangement 
is  spoken  of  as  a  galvanic  battery;  at  present  this  term  is  likewise 
applied  to  a  single  cell. 

Electromotive  force.  The  fact  that  electricity  flows  continuously 
in  a  closed  circuit  containing  a  galvanic  cell  shows  that  the  cell  has 
the  power  of  setting  electricity  in  motion,  and  this  power  is  desig- 
nated as  electromotive  force  (E.  M.  F.),  electrical  tension,  or  potential. 
It  is  the  result  of  the  tendency  to  re-establish  equilibrium,  and 
depends  upon  the  difference  in  the  electrical  condition  of  the  two 
plates ;  the  greater  this  difference  the  greater  the  E.  M.  F. 

The  action  of  an  electric  battery  may  be  compared  to  a  pump  sending  water 
from  a  reservoir  through  a  pipe  to  a  higher  elevation ;  the  water  will  return  to 
its  former  level  with  a  certain  force,  depending  on  the  height  to  which  it  has 
been  lifted,  and  the  water  while  descending  can  be  made  to  do  mechanical 
work — turn  a  wheel  or  set  in  motion  other  machinery.  Similarly  the  cur- 
rent of  electricity  on  its  return  trip  can  be  made  to  do  work,  and  the  quantity 
of  it  depends  on  the  E.  M.  F.  generated  by  the  battery. 

Electric  units.  For  obvious  reasons,  it  is  desirable  to  measure  the 
intensity  and  quantity  of  electric  currents  similarly  as  heat  or  other 
forms  of  energy  are  measured.  The  three  chief  units  adopted  for 
such  measurements  are  named,  in  honor  of  three  great  pioneers  in 
electricity,  the  ohm,  the  ampere,  and  the  volt. 

It  has  been  stated  that  we  differentiate  between  conductors  and 
non-conductors,  but  even  the  best  conductors  offer  resistance  to  the 
passage  of  an  electric  current.  The  unit  of  this  resistance  is  called 
the  ohm,  and  represents  the  resistance  to  a  current  in  a  column  of 
mercury  having  a  section  of  1  square  millimeter  and  a  length  of 
106.28  centimeters,  at  a  temperature  of  0°  C.  For  practical  pur- 


ELECTRICITY.  77 

poses,  sets  of  coils,  known  as  resistance  coils,  having  a  known  resist- 
ance, are  used  for  measuring  electrical  resistance. 

An  ampere  is  the  unit  of  quantity  of  current,  which  may  be  deter- 
mined by  measuring  the  amount  of  oxygen  and  hydrogen  liberated 
by  the  current  from  water  within  a  given  time. 

The  weight  of  copper  deposited  electrolytically  by  the  current  is  used  also 
as  a  means  of  determining  its  amperage.  One  ampere  of  current  deposits  1.177 
grammes  of  copper  per  hour.  For  practical  purposes,  instruments  known  as 
amperemeters,  or  ammeters,  are  used  for  measuring  amperage;  use  is  made  in 
these  instruments  of  the  fact  that  a  current  deflects  a  magnetic  needle,  which 
is  made  to  move  over  a  dial-face  graduated  in  amperes. 

In  using  electric  currents  for  medical  purposes,  1  ampere  is  often  too  strong 
for  the  tissues  of  the  body.  For  this  reason  the  unit  is  divided  into  1000  parts, 
each  part  being  designated  as  a  milliampere. 

The  volt  is  the  unit  for  electromotive  force,  and  is  the  pressure 
required  to  maintain  a  current  of  1  ampere  through  a  resistance  of 
1  ohm. 

The  relation  existing  between  these  three  units  is  expressed  in 
Ohm's  law  :  The  strength  of  the  current  is  equal  to  the  E.  M.  F. 
divided  by  the  resistance  of  the  current. 

The  chief  diiference  between  frictional  and  galvanic  electricity  is 
that  the  first  is  of  high  tension  but  small  in  amount,  while  current 
electricity  is  of  low  tension  but  greater  in  amount. 

Electromagnets.  When  a  piece  of  insulated  wire  is  wound  in 
spiral  form  around  a  bar  of  soft  iron,  and  an  electric  current  is  made 
to  pass  through  the  wire,  the  iron  becomes  a  magnet  for  the  time 
being,  and  is  then  called  an  electromagnet.  If  a  piece  of  steel  is 
treated  in  the  same  way,  it  remains  a  magnet  even  after  the  current 
is  broken,  or  after  it  has  been  taken  from  the  spiral. 

As  the  strength  of  an  electromagnet  is  proportional  to  the  strength 
of  the  current  and  the  length  of  wire  wound  around  it,  electromagnets 
of  very  much  greater  power  than  ordinary  magnets  can  be  made 
The  position  of  the  north  and  south  poles  of  the  magnet  depends  on 
the  direction  of  the  current,  a  reversion  of  the  latter  producing  a 
reversion  of  the  polarity  in  the  electromagnet.  Practical  use  is  made 
of  the  electromagnet  in  telegraph  instruments,  in  the  telephone,  the 
electric  bell,  and  in  many  other  contrivances. 

Electricity  generated  by  magnetism.  Not  only  can  magnets  be 
made  by  subjecting  iron  to  the  influence  of  electric  currents,  butj 


78  CHEMICAL  PHYSICS. 

vice  versa,  electric  currents,  termed  magneto-electric  currents,  can  be 
generated  by  the  action  of  magnets  on  metallic  wires.  Indeed,  when- 
ever a  magnet  is  brought  near  to,  or  taken  away  from,  a  wire,  or  is 
moved  about  in  its  neighborhood  ;  or  if,  vice  versa,  a  mass  of  wire  is 
moved  around  a  magnet — i.  e.,  whenever  metallic  wires  are  made  to 
pass  through  a  magnetic  field — temporary  electric  currents  are  always 
set  up  in  the  wire.  These  induced  currents  are  the  result  of  the 
conversion  of  mechanical  energy — i.  e..  the  energy  required  to  move 
a  wire  or  a  magnet — into  electrical  energy. 

Use  is  made  of  these  facts  for  the  generation  of  electric  currents 
by  suitably  constructed  machines,  known  as  magneto-electric  machines. 
In  the  smaller  ones  a  permanent  horseshoe  magnet  is  used.  Between 
or  in  front  of  its  poles  revolve  two  coils  of  insulated  wire  with  soft 
iron  cores,  known  as  armatures.  During  rapid  revoluting  the  soft 
iron  cores  are  magnetized  while  opposite  one  of  the  poles  of  the  per- 
manent magnet,  demagnetized  while  equidistant  from  the  two  poles, 
and  reversed  while  passing  to  the  opposite  pole.  The  magnetization 
and  demagnetization  of  the  iron  cores  have  the  same  effect  on  the 
coils  of  wire  as  if  a  magnet  were  suddenly  introduced  into  the  coil 
and  as  quickly  withdrawn.  Thus  currents  will  be  induced  in  the 
wire,  and  they  will  run  in  opposite  directions  as  the  polarity  of  the 
cores  changes  with  each  half  revolution.  Such  currents  are  known 
as  alternating  currents. 

The  same  principle  is  made  use  of  in  the  dynamo-electrical  machines 
for  generating  the  currents  employed  for  motive  power,  electric 
lighting,  etc.  Instead  of  permanent  magnets,  powerful  electro- 
magnets are  here  used,  and  in  place  of  an  armature  with  two  coils 
of  wire,  armatures  with  many  coils  are  employed.  Moreover,  an 
arrangement  known  as  the  commutator  is  often  used  to  change  the 
alternating  to  a  direct  or  continuous  current — i.  e.,  the  generated 
electricity  is  collected  in  such  a  manner  that  it  moves  in  one  direction 
continuously. 

Electric  motors  are  essentially  dynamos  in  which  the  action  is  re- 
versed— i.  e.,  electric  currents  convert  iron  into  electromagnets,  which 
by  successive  attraction  and  repulsion  of  the  iron  in  the  armature 
cause  its  rapid  rotation,  which  motion  may  be  communicated  to  other 
machinery. 

Voltaic  induction.  It  has  been  mentioned  that  a  body  charged 
with  static  electricity  causes,  by  induction,  an  electric  disturbance  in 
all  bodies  near  by.  Similarly  an  electric  current  passing  through 


ELECTRICITY. 


79 


one  wire  sets  up  induced  currents  in  neighboring  wires.  One  of  the 
principal  applications  made  of  these  induced  currents  is  in  the  induc- 
tion coil,  or  Ruhmkorf  coil,  shown  diagrammatically  in  Fig.  30.  It 
consists  of  a  hollow  cylinder  covered  with  a  coil  of  insulated  and 
relatively  coarse  wire,  P,  connected  with  a  battery,  B.  Over  this 
first  or  primary  coil  is  wound  another,  the  secondary  coil,  S,  com- 
posed of  much  longer  and  finer  wire. 

FIG.  30. 


Induction  coil. 

While  a  current  passes  through  the  primary  wire  nothing  is  noticed 
in  the  secondary  wire,  but  the  instant  the  current  is  closed  an  instan- 
taneous induced  current  is  set  up  in  the  secondary  wire  in  one  direc- 
tion, and  on  opening  the  circuit  in  the  opposite  direction.  It  follows 
that  it  requires  a  rapid  closure  and  opening  of  the  circuit  to  generate 
electricity  in  the  secondary  coil.  The  opening  and  closing  of  the 
current  are  accomplished  by  the  following  self-acting  arrangement. 
In  the  hollow  portion  of  the  primary  coil  are  placed  bars  of  soft  iron, 
which  are  magnetized  whenever  a  current  passes  through  the  coil. 
Near  one  terminal  of  the  iron  bars  is  a  movable  metallic  hammer,  H, 
held  by  a  spring  in  such  a  position  that  the  current  is  closed  by  it. 
When  the  bars  are  magnetized,  they  raise  the  hammer,  thereby  open- 
ing the  circuit ;  the  cessation  of  the  current  causes  the  iron  to  be  de- 
magnetized and  the  hammer  falls  to  its  original  position,  closing  the 
circuit,  and  this  action  continues  as  long  as  the  current  is  allowed 
to  flow.  This  arrangement,  known  as  a  "  make  and  break "  con- 
trivance, generates,  through  the  very  rapid  opening  and  closing  of 
the  primary  circuit,  in  the  secondary  coil  that  current  which  is  known 
as  secondary,  induced,  interrupted,  or/aradic  current. 

The  object  of  the  induction  coil  is  to  generate  from  a  battery  current  of  low 
E.  M.  F.  induced  currents  of  very  high  E.  M.  F.  The  effectiveness  of  the 


80 


CHEMICAL  PHYSICS. 


induction  coil  increases  with  the  length  of  its  wire,  which  in  large  instruments 
is  fifty  miles  and  more.  While  such  machines  are  in  operation  sparks  several 
feet  in  length  will  pass  between  the  terminals  of  the  secondary  coil  at  A. 

Conversion  of  electrical  energy  into  heat  and  light.  "When- 
ever a  current  passes  through  a  wire  (or  through  any  other  mass)  it 
offers  more  or  less  resistance,  the  amount  of  which  depends  on  the 
nature  of  the  material  and  the  thickness  of  the  wire.  This  resistance 
gives  rise  to  the  conversion  of  electrical  energy  into  heat.  Practical 
use  is  now  extensively  made  of  these  heating  effects  by  passing  strong 
currents  through  poor  conductors,  as  is  done  in  the  heaters  used  for 
heating  cars  or  buildings,  in  stoves  for  cooking  purposes,  in  the 
vulcanizers  used  in  dental  operations,  and  in  electric  furnaces.  In 


M 


Electric  furnace. 


the  latter,  powerful  currents  are  employed  to  produce  temperatures 
unattainable  by  processes  of  combustion  or  by  any  other  means  at 
our  disposal.  These  furnaces  have  not  only  revolutionized  many 
processes  of  manufacture,  but  have  led  to  the  discovery  of  a  number 
of  substances. 

The  construction  of  electric  furnaces  differs  widely  according  to 
the  use  made  of  them.  Fig.  31  represents  the  vertical  section  of  a 
furnace  used  for  the  manufacture  of  aluminum-bronze.  The  material 
to  be  acted  on  is  contained  in  a  graphite  crucible,  A,  resting  on  the 


ELECTRICITY. 


81 


metallic  plate  P,  and  surrounded  by  a  mass  of  carbon,  C,  the  whole 
being  enclosed  by  the  furnace  wall  M.  D  is  a  carbon  rod,  and  acts 
as  the  anode,  while  connection  through  the  metallic  plate  is  made 
with  the  cathode  from  below. 

Fig.  32  gives  a  sectional,  and  Fig.  33  an  exterior,  view  of  an  elec- 
tric furnace  used  in  the  manufacture  of  carborundum.     The  current 

FIG.  32. 


Longitudinal  section  of  carborundum  furnace. 

enters  and  leaves  through  the  cables  which  terminate  in  carbon  elec- 
trodes fastened  in  the  wall.     Between  the  electrodes  is  a  mass  of 

FIG.  33. 


Exterior  view  of  carborundum  furnace. 

coke,  which,  while  conducting  the  current,  offers  sufficient  resistance 
to  be  heated  to  an  extremely  high  temperature.  (For  details  of  the 
chemical  action  see  the  article  on  Carborundum.) 

The  electric  arc  lamp  and  the  incandescent  lamp  are  well-known  examples 
of  the  conversion  of  electrical  energy  into  light.     In  the  former  lamp  electricity 
6 


82 


CHEMICAL  PHYSICS. 


FIG.  34. 


of  very  high  electromotive  force  (1000-3000  volts)  passes  between  terminals  of 
pencils  of  hard  carbon,  which,  while  infusible,  burn  away  gradually,  requiring 
an  automatically  acting  contrivance  to  keep  the  two  pencils  at  a  constant  dis- 
tance. In  the  incandescent  lamp  a  filament  of  carbon,  fastened  in  an  exhausted 
glass  globe,  is  heated  to  a  white  heat  by  a  current  of  about  50  to  120  volts. 

Conversion  of  electrical  energy  into  chemical  action.    A  highly 
important  effect  of  electric  currents  is  their  power  to  cause  chemical 
decomposition — i.  e.,  the  splitting-  up  of  matter  into  two  of  its  com- 
ponent parts.     Thus,  if  the  terminals  of  a  battery  are  placed  in  a 
vessel  with  acidified  water,  gas-bubbles  rise  from 
both  terminals,  and  on  examination  the  gases 
are  found  to  be  hydrogen  and  oxygen,  which 
are  the  constituents  of  water.     In  order  to  col- 
lect the  gases  and  measure  their  volume,  the 
apparatus  shown  in  Fig.  34  may  be  used.     It 
consists  of  three  connected  glass  tubes,  which 
are  filled  with  water  acidified   with  sulphuric 
acid.      The   electric   current  is    made   to  pass 
through  the  liquid  from  the  poles,  in  this  case 
preferably  pieces  of  platinum  foil  fastened  to 
platinum  wire  fused   in  the  glass  tubes.     On 
passing  a  current  through  the  liquid,  oxygen 
rises  from  the  positive,  and  hydrogen  from  the 
negative  pole.     The  process  of  splitting  up  a 
compound   body  by   electricity   is  called   elec- 
trolysis ;   the  bodies  undergoing  decomposition 
are  termed  electrolytes.    The  metallic  conductors 
by  which  the  current  enters  and  leaves  a  liquid 
or  gaseous  electrolyte  are  called  poles  or  elec- 
trodes, and  are  designated  by  the  same  names 
given  to  the  plates  in  the  generating  cell — i.  e., 
they  are  called  positive  (  +  )  pole  or  anode,  and  negative  (  —  )  pole 
or  cathode.      The  decomposition  product  appearing  at  the  positive 
pole  is  said  to  be  electronegative,  the  one  appearing  at  the  nega- 
tive pole  is  electropositive. 


Electrolysis  of  water. 


Electropositive  are : 
Hydrogen, 
Metals, 
Bases  and  basic  radicals. 


Electronegative  are : 
Oxygen, 

Halogens  (chlorine,  etc.), 
Acids  and  acid  radicals. 


When  an  electric  current  passes  through  a  solution  of  any  salt, 
this  is  split  up  into  the  base  and  the  acid  composing  the  salt.     If 


ELECTRICITY.  83 

the  base  be  a  metal,  such  as  copper,  it  will  be  deposited  on  the  elec- 
tronegative pole.  Use  is  made  of  this  property  in  the  different 
processes  of  electroplating  and  electrotyping.  Among  the  metals 
requiring  the  weakest  current  for  their  electrolytic  precipitation  are 
copper,  silver,  gold,  and  nickel,  and  these  are  often  precipitated  upon 
other  metals  which  form  the  negative  pole. 

Electrolysis  is  used  also  on  a  large  scale  for  separating  metals  from 
ores,  or  from  one  another,  and  on  a  small  scale  for  analytical  opera- 
tions ;  it  also  plays  an  important  part  in  the  work  done  by  the  elec- 
tric furnace,  in  which  often  both  the  required  high  temperature  and 
the  decomposing  influence  are  furnished  by  the  electric  current. 

Discharge  through  gases.  When  an  electric  current  of  suffi- 
ciently high  E.  M.  F.  is  discharged  through  a  gas,  for  instance, 
through  air,  the  gas  is  rendered  luminous  by  its  passage — i.  e.,  we 
have  what  is  called  an  electric  spark,  in  appearance  like  that  of  a  flash 
of  lightning.  This  spark  in  many  cases  exerts  chemical  action,  as, 
for  instance,  when  oxygen  is  converted  into  ozone,  which  change  will 
be  considered  later. 

If  the  discharge  take  place  in  a  gas  inclosed  in  a  glass  globe  from 
which  the  gas  may  be  removed  by  means  of  an  air-pump,  it  is  found 
that  at  a  sufficiently  reduced  pressure  the  spark  ceases  and  the  inte- 
rior of  the  globe  assumes  a  beautiful  luminosity,  the  nature  of  which 
depends  on  the  kind  of  gas  operated  on. 

By  exhausting  the  air  from  suitably  constructed  bulbs  or  tubes 
still  further  until  an  almost  perfect  vacuum  is  obtained,  the  electric 
discharges  passing  through  this  vacuum  again  show  decided  changes. 
If  the  cathode  of  such  a  vacuum  tube  be  formed  of  a  metallic  disk, 
while  the  anode  be  a  straight  wire,  then  on  passing  the  current 
through  the  vacuum  tube  a  pale  purplish  beam  of  light  radiates  from 
the  face  of  the  disk.  This  beam  is  known  as  the  cathode  ray ;  it  has 
been  shown  to  consist  of  streams  of  portions  of  matter  negatively 
charged,  and  moving  with  great  velocity. 

Rontgen  rays.  During  the  generation  of  the  cathode  rays  in  the 
vacuum  tube  another  kind  of  rays  of  a  very  peculiar  character  are  formed. 
They  have  been  called  Rontgen  rays,  after  their  discoverer,  who  him- 
self named  them  x-rays.  These  rays  differ  from  other  rays  in  many 
respects ;  thus  they  can  pass  readily  through  many  kinds  of  matter 
which  are  opaque  to  ordinary  light ;  they  cause  many  substances  tg 
emit  light  when  they  fall  upon  them  ;  they  affect  photographic  plates, 


84  CHEMICAL  PHYSICS. 

and  have   a  decided   physiological   action   on  various  parts  of  the 
human  body. 

Radio-activity.  In  1896  the  French  scientist  Becquerel  dis- 
covered that  the  metal  uranium  and  its  compounds  exert  sponta- 
neously and  continuously  a  certain  influence  upon  their  surroundings. 
This  influence  was  found  to  be  due  to  rays  (now  called  Becquerel 
rays)  of  a  peculiar  kind.  They  act  upon  the  photographic  plate ;  they 
pass  through  black  paper  and  metals  ;  they  render  the  gases  through 
which  they  pass  conductors  of  electricity  ;  they  cannot  be  reflected  or 
refracted.  Any  substance  exhibiting  the  power  of  sending  out  such 
rays  is  said  to  be  radio-active.  Besides  uranium  and  its  compounds 
those  of  thorium  were  found  to  possess  the  same  properties. 

The  subject  of  radio-activity  was  next  studied  by  Madam  Curie, 
who  showed  that  certain  minerals  (such  as  pitch-blende)  contain- 
ing uranium  are  more  radio-active  than  uranium  itself,  and  in  the 
course  of  her  investigation  demonstrated  that  in  uranium  ores  are 
several  substances  which  show  radio-activity  to  a  remarkable  extent. 

The  work,  carried  yet  farther  by  a  number  of  scientists,  has 
brought  out  the  following  results  :  Three  substances,  named  polonium, 
actinium,  and  radium,  have  been  obtained  from  pitch-blende  and 
show  a  radio-activity  a  million  times  greater  than  that  of  uranium 
or  thorium. 

Of  these  three  substances  at  least  one — the  radium — has  been  posi- 
tively proven  to  be  an  elementary  substance  of  metallic  nature  form- 
ing well-defined  salts,  such  as  radium  chloride  and  bromide.  Radium 
salts  show  all  the  previously  mentioned  properties  of  Becquerel  rays, 
but  in  addition  they  exhibit  some  other  features. 

Thus,  radium  salts  are  permanently  luminous  and  render  luminous 
(or  phosphorescent)  for  a  shorter  or  longer  period  a  great  number  of 
other  substances.  The  most  sensitive  are  barium  platinocyanide,  zinc 
sulphide,  diamond,  etc.  Not  only  do  radium  salts  impart  luminosity 
to  other  substances,  but  these  salts  communicate  little  by  little  their 
radio-active  properties  to  substances  in  their  neighborhood,  and  these 
in  turn  emit  Becquerel  rays  for  some  time. 

Another  startling  discovery  was  made  when  it  was  shown  that 
radium  salts  develop  heat  continuously,  and  consequently  are  in 
themselves  warmer  than  their  surroundings.  A  small  flask  containing 
0.7  gramme  of  radium  bromide  shows  a  temperature  of  3°  C.  higher 
than  the  surrounding  air.  Calorimetric  measurements  have  shown 
that  radium  bromide  evolves  enough  heat  to  convert  per  hour  its  own 


ELECTRICITY.  85 

weight  of  ice  into  water,  or  that  one  gramme  of  radium  bromide  will 
raise  the  temperature  of  80  grammes  of  water  one  degree  C.  per 
hour. 

Just  as  sun  rays  are  made  up  of  heat  rays,  light  rays,  and  rays  of 
actinic  power,  so  it  has  been  found  that  there  is  a  difference  in  the 
rays  of  a  radio-active  body.  There  are  at  least  three  kinds,  of  which 
the  first  group,  called  alpha  rays,  possesses  remarkable  penetrating 
power  and  great  photographic  energy ;  they  are  not  deviated  from 
their  path  under  the  influence  of  a  magnetic  field,  and  resemble  the 
Rontgen  rays  in  their  action.  The  beta  rays  produce  heat,  are  devi- 
able  under  the  influence  of  a  magnetic  field,  and  resemble  cathode 
rays.  The  third  group — gamma  rays — is  easily  absorbed. 

Of  great  interest  is  the  physiological  action  of  radium  compounds 
on  the  animal  system.  Radium  bromide,  even  when  enclosed  in  a 
wooden  or  metallic  box,  brought  near  the  closed  eye  causes  the  sensa- 
tion of  light.  While  nothing  is  felt  when  radium  salts  are  brought 
close  to  our  body,  yet  a  strong  influence,  similar  to  that  of  Rontgen 
rays,  is  exerted  upon  the  tissues.  This  is  shown  by  the  fact  that  days 
or  weeks  after  the  body  had  been  exposed  to  radium  rays  the  skin 
reddens  and,  if  the  exposure  was  of  sufficient  duration,  sores  and 
ulcerations  will  form  which  require  a  long  time  for  healing.  A  sealed 
glass  tube,  containing  a  little  radium  bromide,  when  placed  in  a  bowl 
of  water  with  small  fishes  will  cause  their  death  in  a  few  hours. 
Attempts  are  now  being  made  to  use  radium  rays  like  Rontgen  rays 
in  the  treatment  of  skin  diseases,  lupus,  etc. 

When  the  apparently  never-diminishing  power  of  radium  to  give 
out  continuously  light  and  heat  was  discovered,  it  appeared  as  if  our 
views  regarding  matter  and  energy  were  completely  upset.  A  closer 
investigation,  however,  has  shown  that  this  apparently  unlimited 
source  of  energy  may  be  explained  in  a  way  conforming  to  our  pre- 
vious views. 

What  is  supposed  to  take  place  is  this :  All  radio-active  substances 
send  out  with  enormous  velocity  particles,  called  corpuscles,  which  are 
a  thousand  times  smaller  than  a  hydrogen  atom.  This  substance 
which  is  thrown  off,  and  which  Crookes  designates  the  fourth  state  of 
matter,  or  radiant  matte)*,  is  called  emanation.  The  phenomena  of 
radio-activity,  previously  described,  are  due  to  these  emanations 
which  cause  a  bombardment  of  everything  lying  in  their  paths. 

The  discovery  of  radiant  matter  has  modified  our  views  regarding 
atoms.  It  is  now  believed  that  the  atom,  as  revealed  in  chemistry,  is 
a  mass  of  a  great  number  of  small  corpuscles  which  have  come  to  a 


86  CHEMICAL  PHYSICS. 

state  of  stability  or  equilibrium,  in  which  state  they  cannot  be  sepa- 
rated by  our  ordinary  chemical  operations,  and  thus  appear  as  single 
units  or  atoms.  In  radium  and  in  other  radio-active  bodies  these 
complexes  of  corpuscles  are  in  unstable  equilibrium  and  possess 
potential  energy  which  has  a  tendency  to  diminish  in  quantity,  thus 
causing  the  state  of  unrest  exhibited  by  radio-active  bodies.  The 
potential  energy  becomes  kinetic  in  the  form  of  heat,  light,  etc.,  and 
meantime  the  complexes  are  transformed  to  stable  forms  which  do  not 
possess  radio-activity  and  which  act  like  the  chemical  atoms. 

This  would  involve  the  transformation  of  one  element  into  a  new 
element.  And  that  is  exactly  what  has  been  found  to  take  place  in 
the  case  of  radium,  namely,  that  the  emanation  from  radium  contains 
helium.  (For  the  manufacture  of  radium  compounds,  see  the  article 
on  Radium.) 

QUESTIONS. — Name  some  conductors  and  non-conductors  of  electricity,  and 
explain  their  behavior  in  connection  with  electrical  phenomena.  What  is 
meant  by  positive  and  negative,  and  by  static  and  current  electricity  ?  Describe 
three  methods  for  generating  electricity.  Name  the  three  principal  units  used 
in  the  measurement  of  electrical  currents,  and  explain  the  methods  employed. 
Explain  the  construction  and  action  of  a  galvanic  cell.  What  is  a  permanent 
magnet,  and  what  is  an  electromagnet  ?  How  are  they  made,  and  what  are  their 
characteristic  properties?  Define  the  following  terms:  Anode,  cathode,  circuit, 
electric  current,  induction,  and  electromotive  force.  Describe  construction  of 
the  electric  furnace,  and  explain  its  action.  How  may  electricity  be  used  in 
the  generation  of  heat,  light,  mechanical  motion,  and  chemical  action? 


II. 

PRINCIPLES  OF  CHEMISTRY. 


5.    ELEMENT,    COMPOUND,    CHEMICAL    AFFINITY,    MODES    OF 
EFFECTING    CHEMICAL    CHANGE. 

HAVING  considered  some  of  the  subjects  of  physics,  we  may  now 
pass  to  the  field  of  chemistry.  The  nature  of  a  chemical  change  and 
the  scope  of  chemistry  have  already  been  discussed  on  page  18.  One 
of  the  simplest  means  of  bringing  about  a  change  in  the  composition 
of  matter  is  by  applying  heat.  Let  us  see  what  may  be  learned 
from  the  following  experiment. 

Decomposition  by  heat.  The  results  of  the  action-  of  heat  upon 
matter  have  been  stated  to  be :  Increased  velocity  of  the  motion  of 
molecules,  increase  in  volume  of  the  substance  heated,  and  in  many 
cases  a  conversion  of  solids  into  liquids  and  of  these  into  gases.  Be- 
sides these  results  there  frequently  may  be  noticed  another. 

FIG.  35. 


Decomposition  of  mercuric  oxide  in  A  ;  collection  of  mercury  in  B,  and  of  oxygen  in  C. 

To  illustrate  this  action  of  heat,  we  will  select  the  red  oxide  of 
mercury,  a  solid  substance  which  is  insoluble  in  water,  almost  taste- 
,  and  of  a  brick-red  color.     When  this  oxide  of  mercury  is  placed 

87 


88  PRINCIPLES  OF  CHEMISTRY. 

in  a  glass  tube  and  heated,  it  will  be  found  to  disappear  gradually, 
and  we  might  assume  that  it  has  been  converted  into  a  gas  from 
which,  upon  cooling,  the  red  oxide  of  mercury  would  be  re-obtained. 
If  the  apparatus  for  heating  the  oxide  of  mercury  be  so  constructed 
that  the  escaping  gases  may  be  collected  and  cooled,  we  shall  not  find 
the  red  oxide  in  our  receiver,  but  in  its  place  a  colorless  gas,  while  at 
the  same  time  globules  of  metallic  mercury  will  be  found  deposited 
in  the  cooler  parts  of  the  apparatus  (Fig.  35). 

The  action  of  heat  consequently  has  in  this  case  produced  an  effect 
entirely  different  from  the  effects  spoken  of  heretofore.  There  is  no 
doubt  that  the  first  action  of  the  heat  upon  the  oxide  of  mercury  is 
an  increased  velocity  of  the  motion  of  its  molecules  and  simulta- 
neously an  increase  of  its  volume,  but  afterward  a  decomposition  of 
the  oxide  takes  place,  and  two  substances  are  liberated,  each  different 
from  the  oxide. 

One  of  these  substances  is  a  silvery-wThite,  heavy,  liquid  metal,  the 
mercury ;  the  other  substance  is  a  colorless,  odorless  gas,  which  sup- 
ports combustion  much  more  freely  than  does  atmospheric  air,  and  is 
known  as  oxygen. 

Elements.  We  have  thus  succeeded  in  proving  that  red  oxide  of 
mercury  may  be  converted  or  decomposed  by  the  mere  action  of  heat 
into  mercury  and  oxygen.  It  is  but  natural  to  inquire  whether  it 
would  be  possible  further  to  subdivide  the  mercury  or  the  oxygen 
into  two  or  more  new  substances  of  different  properties.  To  this 
question,  which  has  been  experimentally  propounded  to  Nature  over 
and  over  again,  we  have  but  one  answer,  viz. :  Oxygen  and  mercury 
are  substances  incapable  of  decomposition  by  any  method  or  means 
as  yet  known  to  us.  They  resist  the  powerful  influences  of  electricity 
and  heat,  even  when  raised  to  the  highest  attainable  degrees  of  in- 
tensity, and  they  issue  unchanged  from  every  variety  of  reaction 
hitherto  devised  with  the  view  of  resolving  them  into  simpler  forms 
of  matter. 

Therefore  we  are  justified  in  regarding  oxygen  and  mercury  as  non- 
decomposable  or  simple  substances,  in  contradistinction  to  compound 
or  decomposable  substances,  such  as  the  red  oxide  of  mercury. 

All  substances  which  cannot  by  any  known  means  be  resolved  into 
simpler  forms  of  matter,  are  called  elements;  all  substances  which 
may,  by  one  process  or  another,  be  subdivided  or  decomposed  in  such 
a  manner  that  new  substances  with  new  properties  are  formed,  are 
called  compound  substances  or  compounds. 


ELEMENT,   COMPOUND,    CHEMICAL  AFFINITY,  ETC.          89 

While  the  number  of  known  compounds  exceeds  many  thousands, 
the  number  of  elements  is  comparatively  small,  about  seventy-six  of 
these  simple  substances  being  known  to  exist  on  our  earth.  And  yet 
this  small  number  of  elements,  by  combining  with  each'  other  in  many 
different  proportions,  form  all  that  boundless  variety  of  matter  which 
we  see  in  nature. 

In  the  case  of  oxide  of  mercury  heat  has  evidently  caused  a  weak- 
ening of  the  attractive  force  which  held  the  two  elements,  mercury 
and  oxygen,  together,  thus  permitting  them  to  part  company.  Such 
a  change  is  known  as  decomposition.  But,  in  other  cases,  heat 
increases  the  attraction  between  elements,  so  that  they  unite  to  form 
more  complex  bodies,  which  would  not  occur  at  ordinary  tempera- 
ture. Such  a  change  is  known  as  combinatioyi .  For  example,  mag- 
nesium metal  does  not  unite  with  the  oxygen  of  the  air  at  ordinary 
temperature,  but  when  heated  sufficiently,  it  unites  with  oxygen 
with  great  vigor.  In  fact,  mercury  unites  with  oxygen  when  heated 
to  a  temperature  a  little  below  its  boiling-point,  and  forms  the  red 
oxide,  but  if  the  latter  is  heated  to  a  higher  temperature  it  is  decom- 
posed. 

The  student  must  not  think  that  elements  are  obtained  in* all  cases 
of  decomposition  by  heat.  In  some  instances  the  new  products  ob- 
tained are  themselves  compounds,  while  in  others  an  element  and  a 
new  compound  result.  For  example,  when  calcium  carbonate  is 
heated  (see  page  18),  calcium  oxide,  a  solid  compound,  and  carbon 
dioxide,  a  gaseous  compound,  are  obtained.  When  potassium  chlor- 
ate, a  compound  of  potassium,  chlorine,  and  oxygen,  is  heated,  the 
element  oxygen  is  evolved,  while  a  new  compound  composed,  of  po- 
tassium and  chlorine,  and  known  as  potassium  chloride,  remains  as  a 
solid  in  the  vessel. 

The  quantity  of  heat  required  for  decomposition  differs  widely 
according  to  the  nature  of  the  substance.  Some  substances  can  be 
produced  only  at  a  temperature  below  the  freezing-point  of  water, 
a  higher  temperature  causing  their  decomposition  ;  other  substances 
may  be  decomposed  at  temperatures  between  the  freezing-  and 
boiling-points;  others  again,  and  to  these  belong  the  majority  of 
inorganic  compounds,  may  be  raised  to  red  or  white  heat  before  decom- 
position sets  in;  and  still  another  number  of  compounds  have  never 
yet  been  decomposed  by  heat.  Theoretically,  however,  we  assume 
that  all  compounds  may  be  decomposed  by  heat,  should  it  be  possible 
to  raise  it  to  a  sufficiently  high  degree. 


90  PRINCIPLES  OF  CHEMISTRY. 

Decomposition  by  electricity.  It  has  been  shown  in  Chapter  4 
that  electricity  exerts  under  certain  conditions  a  strong  decomposing 
influence  on  many  compounds.  It  was  also  stated  that  this  process 
of  decomposition  is  called  electrolysis,  while  the  term  electrolyte  is 
given  to  the  material  acted  upon.  This  material  must  be  a  conductor 
of  electricity,  and  either  in  the  liquid  or  gaseous  state.  The  electro- 
lyte is  brought  into  the  liquid  state  either  by  melting  it  if  solid  or 
dissolving  it  in  some  other  molten  medium,  or,  as  is  most  frequently 
the  case,  by  dissolving  it  in  water,  which  in  some  cases  is  rendered 
acid  or  alkaline,  before  electrolysis  is  carried  out. 

Electricity  is  widely  used  at  the  present  day  in  chemical  industries 
and  in  quantitative  chemical  analysis.  Some  examples  of  chemicals 
obtained  thus  are  metallic  sodium  and  potassium,  caustic  potash, 
chlorine  which  is  converted  into  bleaching  powder,  potassium  chlor- 
ate, aluminum  by  electrolysis  of  a  solution  of  aluminum  oxide  in 
molten  cryolite,  pure  copper  from  the  impure  product,  pure  iron, 
nitric  acid  by  a  powerful  electric  discharge  through  air. 

Decomposition  by  light.  Another  cause  of  decomposition  is,  in 
many  cases,  the  action  of  light.  The  art  of  photography  is  based 
upon  this  kind  of  decomposition.  Many  substances,  easily  affected 
by  light,  have  to  be  kept  in  the  dark  to  prevent  them  from  being 
decomposed. 

The  phenomena  of  heat,  light,  and  electricity  resemble  each  other  in  so  far 
as  they  are  phenomena  of  motion.  Heat  is  the  consequence  of  the  motion  of 
material  particles  (molecules) ;  light  is  the  consequence  of  the  vibratory  motion 
of  the  hypothetical  medium  ether ;  probably  the  same  is  true  of  electricity. 

These  motions,  in  being  transferred,  have,  as  shown  above,  frequently  the 
tendency  of  splitting  up  the  molecules  of  compound  substances. 

Mutual  action  of  substances  upon  each  other.  As  a  general 
rule,  it  may  be  said  that  no  chemical  action  takes  place  between  two 
substances  both  of  which  are  in  the  solid  state,  because  the  molecules 
do  not  come  in  sufficiently  close  proximity  to  exchange  their  parts. 
The  free  motion  of  the  molecules  in  liquid  or  gaseous  substances 
facilitates  such  a  proximity,  and  consequently  chemical  action.  It  is 
often  sufficient  to  have  but  one  of  the  acting  substances  in  the  gaseous 
or  liquid  state,  while  the  second  one  is  a  solid.  By  converting  two 
solids  into  extremely  fine  powder  and  mixing  them  together  thor- 
oughly, chemical  combination  may  follow,  provided  the  affinity 
between  them  be  sufficiently  strong. 


ELEMENT,   COMPOUND,    CHEMICAL  AFFINITY,   ETC.          91 

Physical  phenomena  accompanying-  chemical  action.  By  a 
careful  observation  of  all  the  details  in  a  great  variety  of  chemical 
actions,  an  intimate  connection  between  physics  and  chemistry  be- 
comes apparent.  A  noteworthy  fact  that  stands  out  prominently  is 
that  in  every  change  in  composition,  energy  in  some  form  is  produced 
or  consumed.  In  the  decomposition  of  red  oxide  of  mercury,  heat 
energy  is  constantly  being  absorbed  and  rendered  latent  as  the  oxide 
separates  into  the  free  elements,  oxygen  and  mercury.  As  soon  as 
the  heat-supply  is  withdrawn  the  decomposition  ceases.  When  mag- 
nesium burns,  that  is,  unites  with  oxygen,  a  great  quantity  of  heat 
and  intense  light  is  produced,  and  the  action  after  starting  is  self-sus- 
taining. "We  have  seen  that  electric  energy  is  consumed  in  bringing 
about  chemical  change.  On  the  other  hand,  chemical  action  under 
proper  control  can  be  made  to  produce  electric  energy,  that  is,  an 
electric  current.  In  some  cases  the  energy  of  light  rays  is  consumed 
in  producing  chemical  change,  for  example,  in  photography.  De- 
composition can  be  accomplished  in  certain  instances  by  mechanical 
energy,  as  violent  trituration,  while,  on  the  other  hand,  the  production 
of  mechanical  energy  by  chemical  action  is  illustrated  by  the  explo- 
sion of  gunpowder  and  movement  of  muscles. 

Chemical  or  internal  energy.  Exothermic  and  endothermic 
actions.  From  the  previous  discussion,  we  learn  that  there  must  be 
another  kind  of  energy  stored  up  in  latent  form  in  matter  which 
under  proper  conditions  is  converted  into  forms  of  energy  with  which 
we  have  already  become  familiar  in  Section  I.  on  Physics ;  namely, 
heat,  electricity,  light,  mechanical  energy.  This  form  of  energy, 
which  is  made  manifest  during  chemical  change,  is  called  chemical 
or  internal  energy.  Every  element  and  compound  should  be  looked 
upon  not  merely  as  consisting  of  certain  kinds  of  matter,  but  also  as 
a  storehouse  of  chemical  energy.  In  many  chemical  changes  part  of 
the  internal  energy  is  liberated  in  forms  which  can  be  measured,  such 
as  heat,  electricity,  etc.  This  portion  is  known  as  free  or  available 
internal  energy,  and  is  different  in  amount  according  to  the  nature  of 
the  substances  concerned  in  the  chemical  change.  For  example,  the 
same  weight  of  various  articles  of  food,  when  undergoing  combustion 
in  the  animal  body,  produces  very  different  amounts  of  heat,  and 
therefore  these  foods  have  different  values  as  fuels  for  keeping  up  the 
temperature  of  the  animal  body. 

Sometimes  it  is  necessary  to  augment  the  internal  energy  of  sub- 
stances from  a  supply  of  energy  such  as  heat,  electricity,  etc.,  in  order 


92  PRINCIPLES  OF  CHEMISTRY. 

to  bring  about  chemical  change.  Indeed,  it  has  been  found  that  all 
chemical  changes  maybe  divided  into  two  classes:  (1)  those  which 
take  place  spontaneously  and  in  which  a  certain  amount  of  the  chem- 
ical energy  of  the  substances  acting  is  liberated  and  converted  into 
some  other  forms  of  energy,  which  thus  become  available  for  use  ;  (2) 
those  which  do  not  take  place  spontaneous!  v,  but  which  must  be  sus- 
tained by  the  addition  of  energy  from  without  to  the  substances  act- 
ing. The  energy  set  free  in  spontaneous  chemical  actions  usually 
appears  as  heat,  and  all  actions  proceeding  with  liberation  of  heat 
are  called  exothermic,  while  those  actions  which  absorb  heat  are  called 
endothermic.  The  study  of  the  energy  changes  in  chemical  actions  is 
very  important  for  a  full  understanding  of  such  actions.  The  study 
of  the  heat  produced  or  absorbed  in  chemical  changes  constitutes  a 
subdivision  known  as  Thermochemistry. 

Chemical  reaction,  in  its  broadest  sense,  refers  to  any  chemical 
change,  but  is  used  more  especially  when  the  intention  is  to  study 
the  nature  of  the  substances  decomposed  or  formed.  The  expression 
reagent  is  applied  to  those  substances  used  for  bringing  about  such 
changes. 

Chemical  affinity.  There  must  be  some  cause  which  enables  or 
even  forces  the  different  elements  to  unite  with  each  other  so  as  to 
form  compound  bodies.  There  must  be,  for  instance,  a  cause  which 
enables  oxygen  and  mercury  to  combine  and  form  a  red  powder. 

This  cause  is  to  be  found  in  the  existence  of  another  form  of 
attraction  which  causes  the  smallest  particles  of  different  elements 
to  unite  to  form  new  substances  with  new  properties.  This  kind  of 
attractive  power  is  called  chemical  force  or  chemical  affinity,  and 
bodies  possessing  this  capacity  of  uniting  with  each  other  are  said 
to  have  an  affinity  for  each  other. 

There  is  a  great  difference  between  chemical  attraction  and  the 
various  forms  of  attraction  spoken  of  heretofore.  Cohesion  simply 
holds  together  the  molecules  of  the  same  substance,  adhesion  acts 
chiefly  between  the  molecules  of  solid  and  liquid  substances,  gravita- 
tion acts  between  masses.  But  all  these  forces  do  not  change  the 
nature,  the  external  and  internal  properties  of  matter ;  this  is  done 
when  chemical  force  or  affinity  is  operating,  when  a  chemical  change 
takes  place. 

For  instance  :  In  a  piece  of  yellow  sulphur  the  molecules  are  held 
together  by  cohesion,  and  we  can  counteract  this  cohesion  by  mechan- 
ical subdivision,  reducing  the  sulphur  to  a  fine  powder ;  or  by  the 


LAWS  AND  THEORIF:S  OF  CHEMISTRY.  93 

application  of  heat  we  can  further  subdivide  the  sulphur,  melt,  and 
finally  volatilize  it ;  or  we  can  throw  a  piece  of  sulphur  into  the  air, 
when  it  will  fall  back  upon  the  earth  in  consequence  of  gravitation  ; 
or  we  can  dip  it  into  water,  when  it  becomes  moist  in  consequence  of 
surface-action.  Yet  in  all  these  cases  sulphur  remains  sulphur. 

It  is  entirely  different  when  sulphur  enters  into  chemical  combina- 
tion exerting  chemical  attraction,  for  instance,  when  it  burns;  this 
means  when  it  combines  with  the  oxygen  of  the  atmospheric  air.  In 
this  case  a  new  substance,  a  disagreeably  smelling  gas,  a  compound  of 
oxygen  and  sulphur,  is  formed. 

It  is^  consequently  a  complete  change  in  the  properties  of  matter 
which  follows  the  action  of  true  chemical  attraction  ;  we  might  define 
affinity  to  be  a  force  by  which  elements  unite  and  new  substances  are 
generated. 

It  should  be  noted  that  affinity  does  not  really  explain  why  chem- 
ical union  takes  place,  why  an  attraction  between  elements  exists. 
It  is  merely  a  term  that  has  come  into  use  to  express  a  fact  that  can 
be  observed  ;  namely,  that  elements  do  unite,  but  why  they  do  so  no 
one  knows.  Likewise  no  one  knows  why  fhe  earth  attracts  bodies, 
although  we  say  it  is  due  to  gravitation.  This  is  simply  equivalent 
to  saving  that  an  attractive  force  exists  between  the  earth  and  bodies 
upon  it,  a  fact  which  anyone  can  observe.  But  no  one  knows  why 
this  force  exists  or  its  nature. 

6.    LAWS  AND  THEORIES  OF  CHEMISTRY.1 

Law  of  the  constancy  of  composition.  This  law,  also  known 
as  the  law  of  definite  proportions,  was  the  first  ever  recognized  in 
chemical  science ;  it  was  discovered  toward  the  close  of  the  18th 
century,  and  may  be  stated  thus  :  A  definite  compound  always  contains 
the  same  elements  in  the  same  proportion;  or,  in  other  words,  All  chemi- 
cal compounds  are  definite  in  their  nature  and  in  their  composition. 

To  make  this  law  perfectly  understood,  the  difference  between  a 
mechanical  mixture  and  a  chemical  compound  must  be  pointed  out. 
Two  powders,  for  instance  sugar  and  starch,  may  be  mixed  together 
very  intimately  in  a  mortar,  so  that  it  seems  impossible  for  the  eye  to 
discover  more  than  one  body.  But  in  looking  at  this  powder  with 
the  aid  of  a  microscope,  the  particles  of  sugar  as  well  as  those  of 

1  The  subject  matters  of  chapters  6,  7,  8,  and  9  are  grouped  together  for  convenience.  It  is 
not  intended  that  they  should  be  taken  up  in  lectures  or  class  work  at  once  after  chapter  5, 
nor  in  the  exact  order  given  here,  but  each  instructor  will  introduce  them  in  what,  to  him, 
seems  the  most  logical  sequence. 


94  PRINCIPLES  OF  CHEMISTRY. 

starch  may  be  easily  distinguished.     The  mixture  thus  produced  is  n 
mechanical  mixture  of.  molecule  clusters. 

It  is  somewhat  different  when  two  substances,  for  instance  two 
metals,  are  fused  together,  or  when  two  gases  or  two  liquids  (oxygen 
and  nitrogen,  water  and  alcohol)  are  mixed  together,  or  when  finally 
a  solid  is  dissolved  in  a  liquid  (sugar  in  water).  In  these  instances 
no  separate  particles  can  be  discovered  even  by  the  microscope.  The 
mixtures  thus  produced  are  mixtures  of  molecules.  Such  mixtures 
always  exhibit  properties  intermediate  between  those  of  their  constitu- 
ents and  in  regular  gradation  according  to  the  quantity  of  each  one 
present.  The  proportions  in  which  substances  may  be  mixed  are 
variable. 

In  a  true  chemical  compound  the  proportions  of  the  constituent 
elements  admit  of  no  variation  whatever ;  it  is  not  formed  by  the 
mixing  of  molecules,  but  by  the  combination  of  molecules;  the  prop-1 
erties  of  a  compound  thus  formed  usually  differ  very  widely  from 
those  of  the  combining  elements. 

Powdered  iron  and  powdered  sulphur  may  be  mixed  together  in  many 
different  proportions.  If  such  a  mixture  be  heated  until  the  sulphur  becomes 
liquid,  the  two  elements,  iron  and  sulphur,  combine  chemically,  but  they  do  so 
in  one  proportion  only,  56  parts  by  weight  of  iron  combining  with  32  parts  by 
weight  of  sulphur,  to  form  88  parts  of  sulphide  of  iron.  If  the  two  substances 
are  mixed  together  in  any  other  proportion  than  the  one  mentioned,  the  excess 
of  one  will  be  left  uncornbined. 

Law  of  multiple  proportions.  While  two  or  more  elements 
may  unite  in  certain  definite  proportions  to  give  one  definite  com- 
pound, it  does  not  follow  that,  under  other  conditions,  they  may  not 
unite  in  other  proportions  to  give  another  entirely  different  com- 
pound, but  still  perfectly  definite  in  its  composition.  Many  such  ex- 
amples are  known  in  chemistry.  Copper  unites  with  oxygen  in  two 
proportions,  forming  two  distinct  oxides.  Tin  does  the  same.  There 
are  four  different  compounds  of  the  elements  potassium,  chlorine,  and 
oxygen,  and  nitrogen  and  oxygen  unite  in  five  different  ways.  In 
1804  John  Dalton,  of  England,  by  a  study  of  such  multiple  com- 
pounds, proposed  the  law  of  multiple  proportions.  He  had  studied 
the  composition  of  two  gaseous  compounds  of  carbon  and  hydrogen, 
and  found  one  (olefiant  gas)  to  contain  6  parts  of  carbon  to  1  part  of 
hydrogen,  while  the  other  (marsh  gas)  contained  6  parts  of  carbon 
to  2  parts  of  hydrogen.  Upon  what  seems  now  to  be  a  slight  basis, 
Dalton  put  forth  his  law,  which,  however,  has  been  verified  by  every 


LAWS  AND   THEORIES  OF  CHEMISTRY.  95 

exact  analysis  since  his  time,  and  which  is  one  of  the  most  important 
foundation-stones  upon  which  the  structure  of  chemical  science  is 
reared.  The  law  of  multiple  proportions  maybe  stated  thus:  If 
tiro  dements,  A  and  B,  are  capable  of  uniting  in  several  proportions, 
the  quantities  of  B  which  combine  with  a  fixed  quantity  of  A  bear  a 
xitnple  ratio  to  each  other. 

Besides  the  above  illustrations  of  the  law,  several  other  examples 
may  be  mentioned.  Sulphur  and  oxygen  unite  in  two  proportions  to 
form  two  distinct  compounds,  one  a  gas  known  as  sulphur  dioxide, 
the  other  a  solid  known  as  sulphur  trioxide.  In  these  the  quantities 
of  oxygen,  united  with  a  fixed  weight  of  sulphur,  are  in  the  ratio  of 

1  :  1 J  or  2  :  3.     There  are  two  sulphides  of  iron,  known  respectively 
as  ferrous   sulphide  and   pyrite ;    in   these  the  weights  of   sulphur 
united  with  a  fixed  weight  of  iron  are  in  the  ratio  of  1  :  2.     The 
phrase  simple  ratio,  in  the  law,  means  in  the  ratio  of  small  whole 
numbers.     This   feature  of  the  law  is  strikingly  illustrated  in  the 
case   of   the   four   compounds   containing   potassium,   chlorine,  and 
oxygen,  in  which  the  variable  weights  of  oxygen  united  with  fixed 
weights  of  potassium  and  chlorine  are  in  the  ratio  of  1:2:3:4; 
also  in  the  case  of  the  five  compounds  of  nitrogen  and  oxygen,  in 
which  the  weights  of  oxygen  united  with  a  fixed  weight  of  nitrogen 
bear  the  ratio  of  1  :  2  :  3  :  4  :  5. 

Combining-  weights  of  elements.  The  proportions  in  which  any 
two  elements  unite  may  be  expressed  by  any  two  figures  which  stand 
in  the  proper  ratio.  Thus  we  may  say  that  water  is  made  up  of 
hydrogen  and  oxygen  in  the  proportions  by  weight  of  1  to  8,  or 

2  to  16,  or  5  to  40.      Similarly  we  may  state  the  composition  of 
ferrous  sulphide  as  7  parts  of  iron  to  4  parts  of  sulphur,  or  56  parts 
of  iron  to  32  parts  of  sulphur.     Expressing  the  composition  of  com- 
pounds thus  in  a  random  manner,  there  seems  to  be  no  relationship 
between  the   relative  quantities   with  which  the  different    elements 
unite  with  one  another.     But  upon  closer  inspection  of  the  propor- 
tions by  weight  in  which  the  elements  unite,  it  is  found  chat  they  can 
be  reduced  to  a  system  of  figures  which  show  a  remarkable  relation- 
ship.    It  is   found,  purely  from   the   results  of  analysis  and  inde- 
pendently of  any  theory,  that  a  certain  figure  can  be  assigned  to  each 
element,  which  has  the  remarkable  property  that  it  or  a  simple  mul- 
tiple of  it  expresses  the  relative  proportion  by  weight  in  which  that 
element   unites   with    the    other   elements.     Chemists   soon    became 
aware  of  the  fact  that  hydrogen  is  the  lightest  of  all  known  matter 


96  PRINCIPLES  OF  CHEMISTRY. 

and  also  that  it  enters  into  union  with  other  elements  in  the  smallest 
proportions.  Hence  in  establishing  the  above-mentioned  system  of 
numbers,  one  part  by  weight  of  hydrogen  is  taken  as  the  standard  of 
reference,  which  offers  the  advantage  that  none  of  the  figures  is  less 
than  unity.  Let  us  illustrate  by  a  few  examples:  One  part  of 
hydrogen  unites  with  35.18  parts  of  chlorine,  35.18  parts  of  chlorine 
unite  with  38.82  parts  of  potassium,  2  X  38.82  parts  of  potassium 
unite  with  15.88  parts  of  oxygen.  But  2x1  parts  of  hydrogen  also 
unite  with  15.88  parts  of  oxygen.  Also  15.88  parts  of  oxygen  unite 
with  64.91  parts  of  zinc,  and  64.91  parts  of  zinc  unite  with  2  X  35.18 
parts  of  chlorine.  Thus  we  see  that  the  figures  in  these  instances  are 
reciprocally  related,  and  the  same  is  true  for  the  figures  assigned  to 
all  the  other  elements.  This  system  of  figures  is  called  combining 
weights,  and  has  a  deep  significance,  which  will  appear  clearer  when 
the  atomic  theory  is  discussed. 

Atomic  theory.  One  of  the  objects  of  men  of  science,  besides 
experimenting  and  observing  facts  and  laws,  is  to  determine  causes^ 
that  is,  to  furnish  an  answer  to  the  question,  Why  do  things  take 
place  as  they  do?  If  the  senses,  even  when  fortified  with  delicate 
instruments,  are  not  sufficiently  refined  to  perceive  the  causes, 
the  philosopher,  with  the  aid  of  his  reasoning  faculties,  tries  to 
imagine  a  cause  which  will  account  in  the  most  satisfactory  manner 
for  what  he  observes.  Such  an  imagined  cause  is  called  an  hypothe- 
sis or  theory.  For  example,  to  account  for  the  uniform  behavior  of 
all  gases  as  summed  up  in  the  Laws  of  Boyle,  Charles,  and  Avogadro, 
it  was  imagined  that  the  nature  of  gases  is  that  they  are  made  up  of 
exceedingly  minute  particles  in  motion,  acting  as  elastic  bits  of 
matter  and  with  practically  no  cohesion  between  them.  This  is 
known  as  the  kinetic-molecular  theory  of  gases,  and  from  it  all  the 
behaviors  of  gases  can  be  deduced  mathematically.  We  may  never 
be  able  to  actually  see  a  gas  particle,  nevertheless  we  are  willing  to 
accept  that  it  exists  as  long  as  the  hypothesis  accounts  satisfactorily 
for  what  is  observed. 

There  must  be  some  reason  for  the  chemical  behavior  of  the 
elements  as  set  forth  in  the  Laws  of  Definite  and  Multiple  Propor- 
tions and  the  fact  that  the  elements  unite  in  proportions  represented 
in  the  system  of  figures  called  combining  weights.  This  cause  must 
lie  in  the  constitution  or  physical  make-up  of  matter.  Reflection 
upon  the  constitution  of  matter  is  not  peculiar  to  modern  science,  for 
the  ancients  had  their  conceptions,  and  some  (Democritus,  Lucretius) 


LAWS  AND   THEORIES  OF  CHEMISTRY.  97 

advocated  a  theory  of  atoms.  But  the  views  of  the  ancients  were 
speculative  and  had  no  physical  basis  resting  upon  experiments,  and 
therefore  were  of  no  service  to  science.  It  was  not  until  1804  that  a 
theory  or  conception  of  matter  was  proposed  by  John  Dalton,  of 
England,  that  had  the  merits  of  being  capable  of  being  put  to  tests 
and  from  which  deductions  could  be  made  that  lent  themselves  to  ex- 
perimental verification.  Dalton's  atomic  theory  holds  that  (1)  elements 
arc  made  up  of  inconceivably  small  particles  which  are  indivisible  in 
chemical  actions  and  called  atoms  (from  the  Greek  dro//oc,  uncut,  or 
not  yet  divided) ;  (2)  the  atoms  not  only  have  definite  weights,  but 
the  atoms  of  any  one  element  have  the  same  weight,  which  is  differ- 
ent from  the  weight  of  the  atoms  of  some  other  element ;  (3)  when 
the  elements  unite  chemically,  the  action  takes  place  between  the 
atoms.  If  we  assume  this  theory  to  be  correct  and  argue  from  it  as 
a  basis,  w«  can  deduce  the  laws  of  definite  proportions  and  multiple 
proportions.  Let  us  suppose  that  two  certain  elements,  A  and  B, 
unite,  and  the  union  is  of  the  simplest  kind  possible,  that  is,  in  each 
instance  an  atom  of  A  is  united  with  an  atom  of  B.  No  matter  what 
the  mass  of  the  resulting  product  may  be,  whether  an  ounce,  pound, 
or  ton,  the  whole  chemical  action  is  simply  a  repetition  throughout 
the  mass  of  what  might  be  called  the  unit  action,  that  is,  the  union 
of  one  atom  of  A  with  one  atom  of  B.  Hence  the  ratio  between 
the  weights  of  the  elements  in  the  resulting  compound,  that  is,  its 
composition,  must  be  the  same  as  the  ratio  between  the  weights  of 
the  aton?  of  A  and  the  atom  of  B.  But  the  weights  of  these  atoms 
arc  definite  and  constant,  hence  the  composition  of  the  compound 
must  be  constant,  or,  in  other  words,  the  compound  is  an  illustration 
of  the  law  of  definite  proportions.  By  a  simple  extension  of  the 
above  argument,  the  law  of  multiple  proportions  may  be  deduced. 
The  theory  also  accounts  for  the  fact  that  if  two  elements  are  brought 
together  in  other  than  certain  proportions,  say  56  parts  of  iron  to  32 
parts  of  sulphur,  after  union  has  taken  place,  part  of  the  one  or  the 
other  element  is  found  uncombined.  It  is  easy  to  see,  too,  that,  if 
the  theory  is  correct,  the  elements  ought  to  combine  according  to  a 
system  of  figures  such  as  were  discussed  above  as  combining  weights, 
for  these  weights  are  bound  to  be  proportional  to  the  weight  of  atoms, 
which  are  definite.  The  atomic  theory  has  been  found  in  accord  with 
the  facts  of  chemistry  for  a  century  or  more,  and  we  are  justified  in 
accepting  it,  although  we  cannot  prove  absolutely  the  existence  of 
atoms. 

7 


'98  PRINCIPLES  OF  CHEMISTRY. 

Atomic  weight.  If  atoms  exist,  they  must  have  weight,  since 
they  are  concrete  masses  of  matter,  and  all  matter  is  attracted  by  the 
earth.  But,  of  course,  it  is  impossible  to  weigh  single  atoms,  and  we 
have  no  knowledge  of  the  absolute  weight  of  an  atom.  It  is  possi- 
ble, however,  to  determine  the  relative  weights  of  the  atoms,  that  is, 
how  many  times  heavier  one  atom  is  than  another.  How  this  is  done 
will  be  briefly  indicated  in  the  next  chapter.  In  any  process  of 
weighing,  we  adopt  a  unit  with  which  to  make  a  comparison.  For 
example,  in  commerce  we  have  a  mass  of  iron  which  is  called  a 
pound,  and  we  say  a  body  weighs  so  many  times  the  mass  of  iron,  or 
so  many  pounds.  We  proceed  similarly  in  the  case  of  atomic 
weights.  We  use  the  weight  of  an  atom  of  one  element  as  the  unit, 
and  compare  the  weight  of  the  atoms  of  the  other  elements  with  it. 
The  thing  to  decide  is,  Which  atom  shall  be  chosen  as  the  unit 
weight  ?  As  was  said  in  discussing  combining  weights,  hydrogen  is 
the  lightest  known  substance,  and  it  unites  with  other  elements  in  the 
smallest  proportions,  hence  its  atom  is  chosen  as  the  unit  weight. 
The  figures  assigned  to  the  other  elements  as  atomic  weights  simply 
signify  how  many  times  heavier  those  atoms  are  than  the  atom  of 
hydrogen.  In  other  words,  the  atomic  weights  are  nothing  more 
than  ratios.  On  the  page  preceding  the  Index  is  a  table  of  the  ele- 
ments, with  symbols  and  atomic  weights. 

Atoms  and  molecules.  In  Section  I,  on  Physics,  we  learned  that 
all  matter  is  made  up  of  exceedingly  minute  particles,  called  mole- 
cules, and,  from  a  chemical  study  of  matter,  we  are  led  to  believe 
that  there  is  another  kind  of  small  particle,  the  atom.  The  atoms 
unite  in  chemical  action  and  form  the  larger  masses  called  molecules. 
The  molecules  of  compounds  consist  of  atoms  of  different  kinds. 
The  elements  also,  like  any  kind  of  matter,  consist  of  molecules, 
which  evidently  must  be  made  up  of  atoms  of  the  same  kind.  There 
are  a  few  exceptional  elements  of  which  the  molecule  consists  of  only 
one  atom,  that  is,  the  molecule  and  atom  of  these  are  identical.  The 
atoms  of  an  element  have  the  power  of  uniting  not  only  with  atoms 
of  a  different  kind,  but  also  with  themselves,  to  form  molecules  of 
the  element.  The  present  conception  as  to  atoms  may  be  summed 
up  in  the  following  definition  :  "Atoms  are  the  indivisible  constitu- 
ents of  molecules.  They  are  the  smallest  particles  of  the  elements 
that  take  part  in  chemical  reactions,  and  are,  for  the  greater  part,  in- 
capable of  existence  in  the  free  state,  being  generally  found  in  com- 
bination with  other  atoms,  either  of  the  same  kind 'or  of  different 
kinds"  (Remsen). 


LAWS  AND   THEORIES  OF  CHEMISTRY.  99 

We  may  define  molecules  as  the  smallest  particles  of  matter  that 
can  exist  in  the  free  state  and  still  retain  all  the  properties  of  the 
substance  to  which  they  belong.  If  we  divide  the  molecule,  we 
destroy  the  properties  of  the  substance  as  we  know  it  in  the  free  state. 

Chemical  symbols.  For  reasons  to  be  better  understood  hereafter, 
chemists  designate  each  element  by  a  symbol,  and  the  first  or  first  two 
letters  of  the  Latin  name  of  the  element  have  generally  been  selected. 
Thus,  the  symbol  of  hydrogen  is  H,  of  oxygen  O,  of  mercury  Hg 
(from  hydrargyrum),  of  sulphur  S,  etc.  These  symbols  designate, 
moreover,  not  only  the  elements,  but  one  atom  of  these  elements. 
For  instance  :  O  not  only  signifies  oxygen,  but  one  atom  or  15.88  parts 
by  weight  of  oxygen  ;  and  Hg,  one  atom  or  198.5  parts  by  weight  of 
mercury. 

Symbols  or  formulas  of  compounds.  By  suitable  experiments 
it  is  possible  for  the  chemist  to  determine  not  only  the  kinds  of  ele- 
ments in  a  compound  and  their  proportions,  but  also  how  many  atoms 
are  in  a  molecule  of  the  substance.  For  the  sake  of  economy  of 
time  and  space  and  to  give  a  better  insight  into  their  nature,  sub- 
stances are  represented  by  formulas,  which  is  a  shorthand  way  of 
telling  what  would  require  many  words.  A  formula  primarily  rep- 
resents the  composition  of  a  molecule,  but  as  any  quantity  of  a  sub- 
stance is  simply  the  sum  of  a  great  multitude  of  molecules  all.  alike, 
the  formula,  in  a  broader  sense,  stands  for  the  substance  itself.  Thus 
we  say  HgO  is  mercuric  oxide,  although  it  shows  the  composition  of 
a  molecule  of  the  oxide,  namely,  that  it  consists  of  one  atom  of  mer- 
cury and  one  atom  of  oxygen. 

The  formulas  are  formed  by  writing  the  symbols  of  the  constituent 
elements  side  by  side,  and  the  number  of  atoms  of  each  element, 
when  more  than  one  atom  is  present,  is  represented  by  a  figure  below 
and  to  the  right  of  the  symbol  of  the  element ;  thus  H2O  means  that 
a  molecule  of  water  consists  of  two  atoms  of  hydrogen  and  one  atom 
of  oxygen  ;  CO2  means  that  the  carbon  dioxide  molecule  consists  of 
one  atom  of  carbon  and  two  atoms  of  oxygen.  A  number  placed  before 
a  formula  signifies  so  many  molecules,  thus  2H2O  means  two  mole- 
cules of  water.  As  the  formulas  represent  the  size  of  the  molecules, 
they  are  called  molecular  formulas,  and  the  sum  of  the  atomic  weights 
of  all  the  atoms  composing  the  molecules  is  called  the  molecular 
weight,  which  shows  how  many  times  heavier  the  molecule  is  than  an 
atom  of  hydrogen. 


100  PRINCIPLES  OF  CHEMISTRY. 

To  establish  a  molecular  formula  requires  a  careful  quantitative  determina- 
tion of  the  proportions  of  the  constituents  of  a  compound;  conversely,  if  we 
know  the  molecular  formula  of  a  compound,  we  can  calculate  from  it  the  rela- 
tive quantities  of  the  elements,  or  the  percentage  composition  of  the  com- 
pound. Also,  if  we  know  the  formula,  and  the  weight  of  one  constituent,  we 
can  calculate  the  weight  of  the  other  constituents,  and  the  total  weight  of  the 
compound.  Let  us  consider  the  red  oxide  of  mercury,  which  has  the  molec- 
ular formula,  HgO.  In  the  molecule  there  is  an  atom  of  mercury  weighing 
198.5  times  as  much  as  an  atom  of  hydrogen,  and  an  atom  of  oxygen  weighing 
15.88  times  as  much  as  an  atom  of  hydrogen.  It  is  evident  that  the  weights 
of  the  mercury  and  oxygen  in  a  molecule  are  to  each  other  as  198.5  : 15.88. 
What  is  true  of  one  molecule  must  be  true  of  any  number  of  molecules,  that 
is,  of  any  quantity  of  oxide  of  mercury;  hence  we  can  conclude  that  in  the 
oxide  there  are  198.5  parts  of  mercury  to  every  15.88  parts  of  oxygen,  making 
198.5  +  15.88  =  214.38  parts  of  oxide.  To  calculate  the  percentage  composi- 
tion, or  parts  per  hundred,  we  use  the  proportions, 

214.38  HgO  :  198.5  Hg :  :  100  HgO  :  x  Hg  and 
214.38  HgO  :  15.88  O    : :  100  HgO  :  x  O. 

Of  course,  in  all  cases  where  there  are  only  two  constituents,  and  we  find  the 
per  cent,  of  one,  the  other  need  not  be  calculated. 

If  we  had  a  quantity  of  oxide  of  mercury  that  we  knew  contained,  say,  30 
parts  of  mercury,  and  we  wanted  to  know  the  weight  of  the  oxygen  present  or 
the  total  weight  of  oxide,  the  following  proportions  would  give  us  the  answers: 

198.5  Hg  :  15.88  O          : :  30  Hg  :  x  O. 
198.5  Hg  :  214.38  HgO  : :  30  Hg :  x  HgO. 

We  learn  from  the  discussion  above  that  the  elements  enter  into  combina- 
tion in  quantities  represented  by  their  atomic  weights,  or  multiples  of  these, 
to  produce  a  quantity  of  compound  represented  by  the  molecular  weight. 

The  law  of  chemical  combination  by  volume,  or  the  Law  of 
Gay-Lussac,  may  be  stated  as  follows  :  When  two  or  more  gaseous 
constituents  combine  chemically  to  form  a  gaseous  compound,  the  volumes 
of  the  individual  constituents  bear  a  simple  relation  to  the  volume  of  the 
product.  The  law  may  be  divided  into  two  laws,  thus  :  1.  Gases 
combine  by  volume  in  a  simple  ratio.  2.  The  resulting  volume  of 
the  compound,  when  in  the  form  of  a  gas,  bears  a  simple  ratio  to  the 
volumes  of  the  constituents.  For  instance  :  1  volume  of  hydrogen 
combines  with  1  volume  of  chlorine,  forming  2  volumes  of  hydro- 
chloric acid  gas  ;  2  volumes  of  hydrogen  combine  with  1  volume  of 
oxygen,  forming  2  volumes  of  water-vapor  ;  3  volumes  of  hydrogen 
combine  with  1  volume  of  nitrogen,  forming  2  volumes  of  ammonia. 

If  the  different  combining  volumes  of  the  gases  mentioned  are 


LAWS  AND   THEORIES  OF  CHPIMISTRY. 


101 


weighed,  it  will  be  found  that  there  exists  a  simple  relation  between 
these  weights  and  the  atomic  or  molecular  weights  of  the  elements. 

For  instance :  Equal  volumes  of  hydrogen  and  chlorine  combine, 
and  the  weights  of  these  volumes  are  as  1:35.18,  which  numbers 
represent  also  the  atomic  weights  of  the  two  elements.  Two  volumes 
of  hydrogen  combine  with  one  volume  of  oxygen,  and  the  weights  of 
the  volumes  are  as  1  :  7.94  or  2  : 15.88,  the  latter  being  the  atomic 
weight  of  oxygen. 


2  Vol  umes 

Hydrochl  j  oric  Acid  gas. 
W  = !  36.18 


2  Vol ;  umes 

j 
Water  i  -vapor 

W  =  j  17.88 


2  Vol  j  umes 
Anna  ;  onia  gas. 
W  =  I  16.93 


2  Vol  umes 
Sulphur  ic  acid  gas. 
Weight  !=B  97.36 


The  above  diagram  shows  the  simple  relation  which  exists  between 
combining  volumes  and  atomic  and  molecular  weights.  It  was, 
besides  other  factors,  the  discovery  of  this  relation  that  led  to  the 
adoption  of  Avogadro's  Law,  which  has  been  stated.  (See  Chapter 
I.,  page  30.) 

Taking  the  law  of  combination  by  volume  and  Avogadro's  Law  as  a  basis  of 
argument,  we  can  prove  directly  in  the  case  of  some  of  the  elementary  gases 
that  their  molecules  consist  of  more  than  one  atom.  One  volume  of  hydrogen 
combines  with  one  volume  of  chlorine  to  give  two  volumes  of  hydrochloric  acid 
gas.  According  to  Avogadro's  Law  the  volume  of  hydrogen  and  chlorine  con- 
tain the  same  number  of  molecules,  and  the  two  volumes  of  product  formed 
must  contain  twice  as  many  molecules  as  does  the  volume  of  hydrogen  or  chlo- 


102  PRINCIPLES  OF  CHEMISTRY. 

rine.  Hence  the  molecules  of  hydrogen  and  chlorine  must  be  divided  to  form 
part  of  a  product  consisting  of  twice  as  many  molecules,  since  each  molecule  of 
hydrochloric  acid  contains  some  hydrogen  and  some  chlorine.  But  if  the  mole- 
•cules  of  hydrogen  and  chlorine  can  be  divided,  they  must  consist  of  more  than 
one  atom.  Everything  that  is  known  about  hydrochloric  acid  justifies  the 
assumption  that  its  molecule  contains  one  atom  each  of  hydrogen  and  chlorine. 
If  this  is  true,  it  follows  then  that  the  molecule  of  hydrogen  and  of  chlorine 
contains  two  atoms.  The  same  kind  of  argument  in  the  case  of  the  union  of 
hydrogen  and  oxygen  to  form  water-vapor,  leads  to  the  conclusion  that  the 
molecule  of  oxygen  contains  at  least  two  atoms.  In  fact,  from  various  experi- 
ments and  processes  of  reasoning,  it  has  been  established  that  the  molecule  of 
nearly  all  the  elements,  in  the  gaseous  state,  consists  of  two  atoms. 

Theory  (Law)  of  equivalents.  Valence,  or  Quantivalence. 
When  one  element  replaces  another  element  in  a  compound,  the 
quantities  of  the  two  elements  are  said  to  be  equivalent  to  each  other, 
and  according  to  the  law  of  equivalents  the  replacement  of  elements 
one  by  another  takes  place  always  in  definite  proportions.  Formerly 
it  was  believed  that  the  atoms  of  all  elements  were  equivalent  one 
with  another ;  accordingly,  atomic  weights  were  frequently  designated 
as  equivalent  weights. 

This  view,  however,  is  not  correct,  as  it  ir>  found  that  one  atom  of 
one  element  frequently  displaces  two  or  more  atoms  of  another 
element.  This  fact,  as  well  as  other  considerations,  has  led  to  the 
assumption  of  the  quantivalence  of  atoms.  This  property  will  be 
understood  best  by  selecting  for  consideration  a  few  compounds  of 
different  elements  with  hydrogen. 

i.  ii.  m.  iv. 

HCl  H20  H3N  H,C 

HBr  H2S  H3As  H4Si 

HI  H2Se  H3P 

We  see  here  that  Cl,  Br,  and  I  combine  with  H  in  the  proportion 
of  atom  for  atom  ;  O,  S,  Se  combine  with  H  in  the  proportion  of  2 
atoms  of  hydrogen  for  1  atom  of  the  other  element ;  N,  As,  P  com- 
bine with  3;  C  and  Si  with  4  atoms  of  hydrogen. 

Moreover,  it  has  been  found  that  the  compounds  mentioned  in 
column  I.  are  the  only  ones  which  can  be  formed  by  the  union  of 
the  elements  Cl,  Br,  and  I  with  H.  They  invariably  combine  in  this 
proportion  only.  Other  elements  show  a  similar  behavior.  For 
instance,  the  metal  sodium  combines  with  chlorine  or  bromine  in  one 
proportion  only,  forming  the  compound  Nad  or  NaBr. 

Looking  at  columns  II.,  III.,  and  IV.,  we  see  that  the  elements 
mentioned  there  combine  with  2,  3,  and  4  atoms  of  hydrogen, 
respectively.  It  is  evident,  therefore,  that  there  must  be  some  pecu- 


LAWS  AND   THEORIES  OF  CHEMISTRY.  103 

liarity  in  the  power  of  attraction  of  different  elements  toward  other 
elements,  and  to  this  property  of  the  atoms  of  elements  of  holding 
in  combination  one,  two,  three,  four,  or  more  atoms  of  other  ele- 
ments the  name  atomicity,  quantivalence,  or  simply  valence,  has  been 
given. 

According  to  this  theory  of  the  valence  of  atoms,  we  distinguish 
univalent,  bivalent,  trivalent,  quadrivalent,  quinquivalent,  sexivalent, 
and  septivalent  elements.  All  elements  which  combine  with  hydro- 
gen in  the  proportion  of  one  atom  to  one  atom  are  univalent,  as,  for 
instance,  Cl,  Br,  I,  F,  and  all  elements  which  combine  with  these  in 
but  one  proportion,  that  is,  atom  with  atom,  bear  the  same  valence, 
or  are  also  univalent,  as,  for  instance,  Na,  K,  Ag,  etc. 

Those  elements  which  combine  with  hydrogen  or  other  univalent 
elements  in  the  proportion  of  one  atom  to  two  atoms  are  bivalent, 
such  as  O,  S,  Se. 

Trivalent  and  quadrivalent  elements  are  those  the  atoms  of  which 
combine  with  3  or  4  atoms  of  hydrogen,  respectively.  Figuratively 
speaking,  we  may  say  that  the  atoms  of  univalent  elements  have  but 
one,  those  of  bivalent  elements  two,  of  trivalent  elements  three,  of 
quadrivalent  elements  four  bonds  or  points  of  attraction,  by  means  of 
which  they  may  attach  themselves  to  other  atoms. 

Elementary  atoms  are  often  named  according  to  their  valence  : 
monads,  diads,  triads,  tetrads,  pentads,  hexads,  and  heptads. 

To  indicate  the  valence  of  the  elements  frequently  dots  or  numbers 
are  placed  above  the  chemical  symbols,  thus  H1,  Ou,  Nm,  Cmi  or  Civ. 

The  bonds  are  often  graphically  represented  by  lines,  thus  : 

H-,    -0-,    -N-,    -0- 

It  is  needless  to  say  that  such  representations  are  merely  symbolical, 
and  express  the  view  that  atoms  have  a  definite  power  to  combine 
with  others. 

When  atoms  combine  with  one  another  the  bonds  are  said  to  be 
satisfied,  and  it  is  graphically  expressed  thus  : 


I  / 

-N- 


H—  Cl,     H—  O—  H    or    O        ,    H-N-H    or    N-H 

XH  \H 

While  the  valence  of  some  elements  is  invariably  the  same  under 
all  circumstances,  other  elements  show  a  different  valence  (this  means 
a  different  combining  power  for  other  atoms)  under  different  condi- 


104  PRINCIPLES  OF  CHEMISTRY. 

tions.  For  instance  :  Phosphorus  combines  both  with  3  and  5  atoms 
of  chlorine,  forming  the  compounds  PC13  and  PC15.  As  chlorine  is 
a  univalent  element,  we  have  to  assume  that  phosphorus  has  in  one 
case  3,  in  another  case  5  points  of  attraction.  Many  similar  instances 
are  known,  and  will  be  spoken  of  later. 

An  explanation  which  is  sometimes  given  in  regard  to  the  variability  of 
the  valence  of  atoms  is  the  assumption  that  sometimes  one  or  more  of  the 
bonds  of  an  atom  unite  with  other  bonds  of  the  same  atom.  If,  for  instance, 
in  the  quinquivalent  phosphorus  atom  two  bonds  unite  with  one  another  a 
trivalent  atom  will  remain. 

It  is  noticed  that  the  valence  of  atoms  in  nearly  all  cases  increases  or  di- 
minishes by  two,  which  could  not  be  otherwise,  if  the  explanation  given  be 
correct.  Thus  chlorine,  the  valence  of  which  generally  is  I.,  may  also  have  a 
valence  equal  to  III.,  V.,  or  VII.,  while  sulphur  shows  a  valence  either  of  II., 
IV.,  or  VI.  Atoms  whose  valence  is  even,  as  in  the  case  of  sulphur,  are  called 
artiadu  ;  those  whose  valence  is  expressed  in  uneven  numbers,  as  chlorine  and 
phosphorus,  are  called  perissads. 

While  it  is  now  being  assumed  that  most  of  the  elements  possess  more  than 
one  valence,  in  consequence  of  the  assumed  power  of  bonds  in  the  same  atom 
to  saturate  one  another,  in  this  book  will  be  mentioned  chiefly  that  valence 
which  the  element  seems  to  possess  predominantly. 

The  doctrine  of  the  valence  of  atoms  has  modified  our  views  of  the 
equivalence  of  atoms.  We  now  say  that  all  atoms  of  a  like  valence 
are  equivalent  to  each  other.  The  atoms  of  each  univalent  element 
are  equivalent  to  each  other,  and  so  of  the  atoms  of  any  other  valence, 
but  two  atoms  of  a  univalent  element  are  equivalent  to  one  atom  of 
a  bivalent  element,  or  two  atoms  of  a  bivalent  element  to  one  atom 
of  a  quadrivalent  element,  etc. 


QUESTIONS. — Define  a  chemical  change  and  state  the  various  modes  of 
effecting  it,  with  examples.  Define  element,  compound,  combination,  and 
decomposition.  About  how  many  elements  exist?  What  is  chemical  energy? 
Define  exothermic  and  endothermic  actions.  What  is  chemical  affinity  and 
how  does  it  differ  from  other  forces?  State  the  law  of  constancy  of  composi- 
tion. What  is  the  distinction  between  a  mixture  and  a  chemical  compound? 
Give  examples  of  each.  State  the  law  of  multiple  proportions.  Give  in  full 
Dalton's  atomic  theory  and  show  how  it  accounts  for  the  laws  of  combination. 
What  is  the  relation  of  atoms  to  molecules?  Define  atomic  and  molecular 
weight.  What  atom  is  chosen  as  the  unit  of  atomic  weights,  and  why?  What 
are  chemical  symbols  and  what  do  they  signify?  Calculate  the  per  cent,  of 
oxygen  and  hydrogen  in  water,  H2O.  What  weight  of  carbon  dioxide,  CO,, 
would  result  from  25  grammes  of  carbon?  What  regularity  regarding  volume 
is  noticed  when  gases  combine?  Define  valence.  What  were  considered  for- 
merly as  equivalent  quantities,  and  what  are  such  at  present?  Mention  some 
univalent,  bivalent,  trivalent,  and  quadrivalent  elements.  What  explanation 
is  offered  for  variable  valence  ? 


DETERMINATION  OF  ATOMIC  WEIGHTS.  105 

7.  DETERMINATION  OF  ATOMIC   AND  MOLECULAR  WEIGHTS.1 

Determination  of  atomic  weights  by  chemical  decomposition. 
The  great  difficulties  originally  encountered  in  the  determination  of 
atomic  weights  cannot  well  be  described  here.  Consideration  will  be 
given  alone  to  the  three  principal  methods  at  present  in  use.  These 
methods  depend  either  on  chemical  action  or  on  physical  properties. 

One  of  the  chemical  methods  used  for  the  determination  of  atomic 
weights  depends  upon  the  determination  of  the  proportions  by  weight  in 
which  the  element,  the  atomic  weight  of  which  is  unknown,  combines 
with  an  element  the  atomic  weight  of  which  is  known.  For  instance : 
If  in  decomposing  a  substance  we  find  it  to  contain  in  72  parts  by 
weight,  16  parts  by  weight  of  oxygen2  and  56  parts  by  weight  of 
another  element,  we  have  a  right  to  assume  the  atomic  weight  of  this 
second  element  to  be  56,  provided,  however,  that  the  compound  is 
actually  formed  by  the  union  of  one  atom  of  oxygen  and  one  atom  of 
the  other  element.  These  56  parts  by  weight  might,  however,  repre- 
sent 2,  3,  or  more  atoms.  If  56  represented  2  atoms,  the  atomic 
weight  would  be  but  28 ;  if  4  atoms,  14. 

As  this  mode  of  determination  gives  no  clue  to  the  number  of 
atoms  present  in  the  molecule,  the  results  obtained  are  liable  to  be 
incorrect.  In  fact,  the  atomic  weights  of  a  number  of  elements  had 
originally  been  determined  incorrectly  by  using  the  above  or  similar 
methods,  and  many  of  these  old  atomic  weights  had  to  be  changed 
(generally  doubled)  in  order  to  obtain  the  correct  numbers. 

Thus,  in  examining  water,  it  was  found  that  it  contained  8  parts 
by  weight  of  oxygen  to  1  part  of  hydrogen,  and  the  conclusion  was 
drawn  that  the  atomic  weight  of  oxygen  was  8,  and  that  the  molecule 
of  water  was  formed  by  the  union  of  one  atom  of  hydrogen  and  one 
atom  of  oxygen.  It  will  be  demonstrated  below  why  we  assume  to- 
day that  the  atomic  weight  of  oxygen  is  16,  and  that  the  molecule  of 
water  is  composed  of  2  atoms  of  hydrogen  and  1  of  oxygen. 

Another  chemical  method  of  determining  atomic  weights  is  the 
replacement  of  hydrogen  atoms  in  a  known  substance  by  the  element 
the  atomic  weight  of  which  is  to  be  determined.  For  instance :  Hy- 
drochloric acid  is  composed  of  one  atom  of  chlorine  weighing  35.2, 
and  one  atom  of  hydrogen  weighing  1,  the  molecular  weight  of  hy- 
drochloric acid  being  36.2.  If  in  this  acid  the  hydrogen  be  replaced 
by  some  other  element,  for  instance  by  sodium,  we  are  enabled  to 
determine  the  atomic  weight  of  sodium  by  weighing  its  quantity  and 

1  The  consideration  of  Chapter  7  should  be  postponed  until  the  student  has  become  famil- 
iar with  chemical  phenomena  generally. 

2  For  purposes  of  discussion,  whole  numbers  are  often  used  in  place  of  exact  atomic  weights 
when  these  contain  decimals. 


106  PRINCIPLES  OF  CHEMISTRY. 

that  of  the  liberated  hydrogen.  Suppose  that  by  the  action  of  36.2 
grammes  of  hydrochloric  acid  on  sodium,  1  gramme  of  hydrogen 
was  replaced  by  23  grammes  of  sodium.  In  that  case  we  would  say 
that  the  atomic  weight  of  sodium  is  equal  to  23. 

The  difficulty  which  was  alluded  to  above  exists  also  in  this  mode 
of  determination  of  atomic  weights,  viz.,  not  knowing  whether  it 
was  actually  one  atom  of  sodium  that  replaced  the  one  part  of  hy- 
drogen, a  doubt  is  left  as  to  whether  or  not  the  determination  is  correct. 

Determination  of  atomic  weights  by  means  of  specific  weights 
of  gases  or  vapors.  It  has  been  stated  before  that  equal  volumes  of 
gases  contain,  under  like  conditions,  the  same  number  of  molecules 
(no  matter  how  few  or  many  the  atoms  within  the  molecules  may  be), 
and  that  the  molecules  of  elements  contain  (in  most  cases)  two  atoms. 
These  facts  give  in  themselves  the  necessary  data  for  the  determina- 
tion of  atomic  weights. 

For  instance:  If  a  certain  volume  of  hydrogen  is  found  to  weigh 
2  grammes,  and  an  equal  volume  of  some  other  gaseous  element  is 
found  to  weigh  71  grammes,  then  the  atomic  weight  of  the  latter 
element  must  be  35.5,  because  2  and  71  represent  the  relative  weights 
of  the  molecules  of  the  two  elements.  Each  molecule  being  com- 
posed of  2  atoms,  these  molecular  weights  have  to  be  divided  by  2  in 
order  to  find  the  atomic  weights,  which  are,  consequently,  1  and  35.5 
respectively. 

In  comparing  by  this  method  oxygen  with  hydrogen,  it  is  found 
that  equal  volumes  of  these  gases  weigh  32  and  2  respectively,  that 
the  atomic  weight  of  oxygen  is  consequently  16,  and  not  8,  as  deter- 
mined by  chemical  methods. 

This  mode  of  determining  atomic  weights  may  be  applied  to  all 
elements  which  are  gases  or  which  may  without  decomposition  be 
converted  into  gas.  There  are,  however,  elements  which  cannot  be 
volatilized,  and  in  this  case  it  becomes  necessary  to  determine  the 
specific  gravity  of  some  gaseous  compound  of  the  element.  The 
element  carbon  itself  has  never  been  volatilized,  but  we  know  many 
of  its  volatile  compounds,  and  these  may  be  used  in  the  determina- 
tion of  its  atomic  weight. 

Determination  of  atomic  weights  by  specific  heat.  Specific 
heat  has  been  stated  to  be  the  quantity  of  heat  required  to  raise  the 
temperature  of  a  given  weight  of  any  substance  a  given  number  of 
degrees,  as  compared  with  the  quantity  of  heat  required  to  raise  the 
temperature  of  the  same  weight  of  water  the  same  number  of  degrees. 


DETERMINATION  OF  ATOMIC  WEIGHTS.  107 

In  comparing  atomic  weights  with  the  numbers  expressing  the  spe- 
cific heats,  it  is  found  that  the  higher  the  atomic  weight  the  lower  tHe 
specific  heat,  and  the  lower  the  atomic  weight  the  higher  the  specific 
heat.  This  simple  relation  may  be  thus  expressed  :  Atomic  weights 
are  inversely  proportional  to  the  specific  heats ;  or  the  product  of  the 
atomic  weight  multiplied  by  the  specific  heat  is  a  constant  quantity 
for  the  elements  examined. 

Elements.          Specific  heat*.  Atomic  weights.          Product  of  specific  heal 

(Water  =  1 .)  X  atomic  weight. 

Lithium,             09408  7  6.59 

Sodium,               0.2934  23  6.75 

Sulphur,              0  2026  32  6  48 

Zinc,                    00956  65  6.22 

Bromine  (solid),  0.0843  79  6.66 

Silver,                  0.0570  107  6.10 

Bismuth,             0.0308  209  644 

An  examination  of  this  table  will  show  this  relation  between 
atomic  weight  and  specific  heat,  and  also  that  the  product  of  atomic 
weight  multiplied  by  specific  heat  is  equal  to  about  6.5.  The  varia- 
tions noticed  in  this  constant  quantity  of  about  6.5  may  be  due  to 
errors  made  in  the  determinations  of  the  specific  heats,  and  subse- 
quent determinations  may  cause  a  more  absolute  agreement. 

However,  the  agreement  is  sufficiently  close  to  justify  the  deduction 
of  a  law  which  says  :  The  atoms  of  all  elements  have  exactly  the  same 
capacity  for  heat.  This  law  was  first  recognized  by  Dulong  and  Petit 
in  1819,  and  is  simply  a  generalization  of  the  facts  stated. 

To  show  more  clearly  what  is  meant  by  saying  that  all  atoms  have 
the  same  capacity  for  heat,  we  will  select  three  elements  to  illustrate 
this  law. 

If  we  take  of  lithium  7  grammes,  of  sulphur  32  grammes,  of  silver 
107  grammes,  we  have  of  course  in  these  quantities  equal  numbers  of 
atoms,  because  7,  32,  and  107  represent  the  atomic  weights  of  these 
elements.  If  we  expose  these  stated  quantities  of  the  three  elements  to 
the  same  action  of  heat,  we  shall  find  that  the  temperature  increases 
equally  for  all  three  substances — that  is  to  say,  the  same  heat  will  be 
required  to  raise  7  grammes  of  lithium  1°,  which  is  necessary  to  raise 
either  32  grammes  of  sulphur  or  107  grammes  of  silver  1°. 

The  quantity  of  heat  necessary  to  raise  the  atom  of  any  element  a 
certain  number  of  degrees  is,  consequently,  the  same.  As  heat  is  the 
consequence  of  motion,  the  result  of  the  facts  stated  may  also  be  ex- 
pressed by  saying :  It  requires  the  same  energy  to  cause  different 
atoms  to  vibrate  with  such  a  velocity  as  to  acquire  the  same  tempera- 
ture, no  matter  whether  these  atoms  be  light  or  heavy. 


108  PRINCIPLES  OF  CHEMISTRY. 

It  is  evident  that  these  facts  give  us  another  means  of  determining 
atomic  weights,  by  simply  dividing  6.5  by  the  specific  heat  of  the  ele- 
ment. The  specific  heat  of  sulphur,  for  instance,  has  been  found  to  be 
0.2026.  6.5  divided  by  this  number  is  31.6,  or  nearly  32.  Originally 
the  atomic  weight  of  sulphur  had  been  determined  by  chemical  methods 
to  be  16,  but  its  specific  heat,  as  well  as  other  properties,  has  shown 
this  number  to  be  but  one-half  of  the  weight,  32,  now  adopted. 

Tt  may  be  mentioned  that  elements  possess  essentially  the  same 
specific  heat  whether  they  exist  in  a  free  state  or  are  in  combination ; 
this  fact  will,  in  many  cases,  be  of  use  in  the  determination  of  atomic 
weights. 

Determination  of  molecular  weights.  From  the  statements 
made  regarding  the  determination  of  atomic  weights,  it  is  evident 
that  we  may  use  a  number  of  methods  for  determining  molecular 
weights,  these  methods  being  to  some  extent  analogous  to  the  former. 

Thus  we  have  methods  which  are  based  entirely  on  chemical  analysis 
or  on  chemical  changes  generally.  If,  for  instance,  the  analysis  of  a 
substance  shows  of  calcium  40  per  cent.,  of  carbon  12  per  cent.,  and 
of  oxygen  48  per  cent.,  we  have  a  right  to  assume  that  the  molecule  is 
made  up  of  1  atom  of  calcium,  1  atom  of  carbon,  and  3  atoms  of 
oxygen,  as  the  atomic  weights  of  these  elements  are  40,  12,  and  16 
approximately.  The  molecular  weight  in  this  case  is  100,  and  the  com- 
position is  expressed  by  the  formula  CaCO3,  but  the  molecular  weight 
might  be  200  and  the  correct  formula  Ca2C2O6.  There  are  actually 
substances  which  contain  such  multiples  of  atoms,  as,  for  instance,  the 
compounds  C2H2  and  C6H6,  and  as  their  percentage  composition  is 
identical,  analytical  methods  are  insufficient  to  indicate  the  number 
of  atoms  contained  in  these  molecules. 

The  second  method,  based  on  Avogadro's  law,  is  applicable  to  all 
substances  which  are  or  can  be  converted  into  gases  or  vapors  without 
decomposition.  Since  equal  volumes  of  all  gases  at  the  same  temper- 
ature and  pressure  contain  the  same  number  of  molecules,  the  weights 
of  equal  volumes  of  gases  must  bear  the  same  ratio  to  one  another  as 
the  weights  of  the  individual  molecules.  But  the  weights  of  mole- 
cules are  in  the  same  ratio  as  the  molecular  weights.  Hence  we 
deduce  the  following  rule  from  Avogadro's  Law  :  Densities  of  gases  at 
the  same  temperature  and  pressure  are  to  each  other  as  their  molecular 
weights.  If  we  know  the  molecular  weight  of  any  gas  and  its 
density,  by  comparing  any  other  gas  with  it  we  can  determine  its  molec- 
ular weight.  As  we  have  seen,  the  molecule  of  hydrogen  is  known 
to  contain  two  atoms,  that  is,  its  molecular  weight  is  2,  if  we  call  the 


DETERMINATION  OF  ATOMIC   WEIGHTS.  109 

weight  of  its  atom  1.  Hydrogen  is  usually  chosen  for  comparison 
with  other  gases.  Suppose  it  is  desired  to  find  the  molecular  weight 
of  oxygen.  One  liter  of  oxygen  at  0°  C.  and  760  mm.  of  pressure 
weighs  1.429  grammes,  one  liter  of  hydrogen  under  the  same  conditions 
weighs  0.08987  gramme.  Hence  by  the  proportion, 

0.08987:1.429  :  :  2:x, 

x  =  1 .429  X  2  -5-  0.08987  =  31.8, 

that  is,  the  molecular  weight  of  oxygen  is  31.8,  or  the  molecule  is  15.9 
times  heavier  than  the  molecule  of  hydrogen. 

If  we  call  the  density  of  hydrogen  1,  and  refer  the  densities  of 
other  gases  to  this  standard,  then  the  figures  indicate  how  many  times 
heavier  the  gases  are  than  hydrogen  under  like  conditions,  or,  what 
comes  to  the  same  thing,  how  many  times  heavier  the  molecules  of  the 
gases  are  than  the  molecule  of  hydrogen.  Hence,  a  simple  rule  for 
finding  molecular  weight  is  to  multiply  the  density  of  a  gas  on  the 
hydrogen  basis  by  2. 

Conversely,  if  we  know  the  molecular  weights  of  two  gases,  and 
the  density  of  one  of  them,  we  can  calculate  the  density  of  the  other 
gas.  The  density  of  any  gas  is  equal  to  the  density  of  hydrogen 
multiplied  by  half  the  molecular  weight  of  the  gas. 

A  third  method,  that  of  Raoult,  is  based  upok  the  fact  that  the 
freezing-point  of  a  liquid  is  lowered  to  the  same  extent  by  dissolving 
in  it  compounds  in  quantities  proportional  to  their  molecular  weights. 
For  example  :  Water  begins  to  solidify  at  32°  F.  (0°  C.),  but  by  dis- 
solving in  it  say  4  per  cent,  of  its  weight  of  a  salt  (the  molecular  weight 
of  which  is  known)  the  freezing-point  is  lowered,  say  1°  C.  If,  then, 
another  salt  (the  molecular  weight  of  which  is  not  known)  be  dissolved 
in  water,  and  it  be  found  that  to  reduce  the  freezing-point  1°  C.  there 
must  be  dissolved  a  quantity  equal  to  7  per  cent,  of  the  weight  of  the 

QUESTIONS. — What  are  the  three  principal  methods  used  for  the  determina- 
tion of  atomic  weights  ?  Why  are  chemical  means  not  always  sufficient  to 
determine  atomic  weights  ?  How  can  the  specific  gravity  of  elements  in  the 
gaseous  state  be  used  for  the  determination  of  atomic  weight?  Describe  a 
method  of  the  determination  of  atomic  weight  by  chemical  means.  State  one 
of  the  reasons  why  the  atomic  weight  of  oxygen  has  been  changed  from  8  to  16. 
What  relation  exists  between  atomic  weight  and  specific  heat?  State  the  law 
of  Dulong  and  Petit.  Suppose  the  specific  heat  of  an  element  to  be  0.1138, 
what  will  its  atomic  weight  be?  Suppose  the  specific  gravity  of  an  elementary 
gas  to  be  14,  what  will  its  atomic  weight  be?  Suppose  214.24  grammes  of  an 
element  replace  2  grammes  of  hydrogen  in  72.36  grammes  of  HC1,  what  will 
the  atomic  weight  of  the  element  be? 


110  PRINCIPLES  OF  CHEMISTRY. 

water  used — then  are  the  molecular  weights  of  the  two  salts  to  each 
other  as  is  4  to  7. 

In  regard  to  this  method  of  Raoult  it  should  be  stated  that  it  is 
applicable  only  to  such  substances  as  do  not  act  chemically  upon  the 
solvent  used,  and  that  the  ratio  of  the  lowering  of  the  freezing-point 
is  not  the  same  for  all  substances,  but  only  for  members  of  the  same 
class  of  substances. 


8.  CHEMICAL  EQUATIONS.  TYPES  OF  CHEMICAL  CHANGE. 
REVERSIBLE  ACTIONS  AND  CHEMICAL  EQUILIBRIUM. 
MASS  ACTION.  ACIDS,  BASES,  SALTS.  RADICAL.  CONSTI- 
TUTIONAL FORMULAS. 

Chemical  equations.  We  have  seen  that  the  composition  of  sub- 
stances can  be  expressed  by  symbols  or  formulas,  which  show  at  a 
glance  the  kind  of  elements  and  their  proportions  present  in  the  sub- 
stances. Similarly,  a  method  of  representing  what  takes  place  in  a 
chemical  change  concisely  and  in  a  way  that  can  be  quickly  grasped 
has  been  devised.  This  is  done  by  means  of  chemical  equations. 
Such  an  equation  is  formed  by  writing  the  formulas  of  the  substances 
that  react  on  the  left  of  the  sign  of  equality,  and  connecting  them  by 
the  sign  +,  and  the  formulas  of  the  products  of  the  reaction  on  the 
right  of  the  sign  of  equality,  also  connected  by  the  -f  sign.  For 
example,  hydrochloric  acid  and  silver  nitrate  mutually  decompose 
each  other  and  give  an  insoluble  white  substance,  silver  chloride  and 
nitric  acid.  This  may  be  represented  thus,  HC1  -f  AgNO3  =  AgCl 
-f  HNO3.  The  +  sign  should  be  read  and,  and  the  =  sign  should  be 
read  gives.  A  chemical  equation  has  nothing  in  common  with  an 
algebraic  one,  except  its  form.  It  cannot  be  factored,  or  in  any  way 
be  handled  as  an  algebraic  equation.  It  is  simply  a  statement  of  facts 
learned  by  experiment.  Until  we  have  learned  beforehand  the  com- 
position of  the  substances  entering  into  chemical  reaction  and  also  of 
the  products  formed,  and  the  proportions  involved,  we  have  no  basis 
upon  which  we  can  legitimately  write  an  equation.  The  unit  of 
chemical  action  is  the  molecule,  and  the  chemical  equations  are  intended 
to  show  the  action  taking  place  between  the  molecules.  Thus,  in  the 
reaction  above,  one  molecule  of  hydrochloric  acid  decomposes  one 
molecule  of  silver  nitrate.  We  often,  however,  read  an  equation  in  a 
broader  and  less  definite  manner,  thus,  in  the  above  case,  we  say 
hydrochloric  acid  decomposes  silver  nitrate  and  gives  silver  chloride 
and  nitric  acid.  When  more  than  one  molecule  is  represented,  a 
numeral  is  placed  before  the  symbol.  The  symbols  2NaCl  and  Na2Cl2 


CHEMICAL  EQUATIONS,  TYPES  OF  CHEMICAL  CHANGE,  ETC.  Ill 

represent  the  same  number  of  atoms  and  the  same  proportions  by 
wciuht  of  the  elements,  but  they  are  quite  different,  for  NaCl  is  the 
actual  size  of  the  molecule,  and  2NaCl  stands  for  two  molecules,  while 
Xa.,CU  represents  a  molecule  double  the  size  of  that  of  sodium  chloride, 
Na(  -1,  as  actually  known.  Often  in  writing  equations,  for  convenience 
we  represent  elements  in  the  atomic  state,  while  in  reality  they  exist 
in  the  molecular  state.  The  equations  are  true,  however,  as  far  as 
proportions  are  concerned.  For  example,  we  represent  the  union  of 
hydrogen  and  oxygen  to  form  water  thus,  H2  +  O  =  H2O,  but  to  be 
in  keeping  with  the  fact  that  molecules  of  hydrogen  and  oxygen  are 
really  involved,  we  should  write  2H2  -|-  O2  =  2H2O. 

Every  correct  chemical  equation  is  correct  mathematically  also — 
i.  e.y  the  sum  of  the  atoms  as  well  as  that  of  the  molecular  weights  of 
the  factors  equals  the  sum  of  the  atoms  and  that  of  the  molecular 
weights  of  the  products  respectively.  For  instance :  Sodium  car- 
bonate and  calcium  chloride  form  calcium  carbonate  and  sodium 
chloride.  Expressed  in  chemical  equation  we  say  : 

NaaCOs  +  CaCl2  =  CaCO3  +  2NaCl. 

Sodium  carbonate  and  calcium  chloride  are  the  factors,  calcium  car- 
bonate and  sodium  chloride  the  products.  Adding  together  the 
molecular  weights  of  the  factors  and  those  of  the  products  we  find 
equal  quantities,  as  follows : 


2Na  =  45.76 
O=11.91 

3O  =  47.64 
105.31 

Ca  =  39.80 
2C1  =  70.36 

-f      "lioTe 

Ca  =  39.80 
C  =  11.91 
3O  =  47.64 

2Na  =  45.76 
2C1  =  70.36 

99.35 

+           316.12 

Chemical  equations  not  only  are  used  for  representing  chemical 
changes,  but  also  are  the  starting-point  in  all  the  chemical  calcula- 
tions in  which  the  quantities  of  substances  entering  into  chemical 
actions,  or  the  quantities  of  the  product  formed,  are  concerned. 

The  above  calculation  teaches,  for  instance,  that  105.31  parts  by 
weight  of  sodium  carbonate  are  acted  upon  by  110.16  parts  by  weight 
of  calcium  chloride,  and  that  99.35  parts  by  weight  of  calcium  car- 
bonate and  116.12  parts  by  weight  of  sodium  chloride  are  formed  by 
tins  action.  These  data  may,  of  course,  be  utilized  to  find  how  much 
calcium  chloride  may  be  needed  for  the  decomposition  of  one  pound 
or  of  any  other  definite  weight  of  sodium  carbonate ;  or  how  much 
of  these  two  substances  may  be  required  to  produce  one  hundred 
pounds,  or  any  other  definite  weight,  of  calcium  carbonate. 

While  in  many  cases  of  chemical  decomposition  the  change  which  is 


112  PRINCIPLES  OF  CHEMISTRY. 

to  take  place  cannot  be  foretold,  but  has  to  be  studied  experimentally, 
there  are  other  chemical  changes  which  can  be  predicted  with  certainty. 
This  is  more  especially  true  in  the  case  of  the  action  of  acids  on 
bases  and  the  action  of  one  salt  on  another  salt.  This  will  be  easily 
seen  when  the  relationship  between  acids,  bases,  and  salts  is  under- 
stood. Among  these  classes  of  compounds  the  results  can  usually  be 
foretold,  and  there  is  little  difficulty  in  representing  the  change  by 
the  proper  equation.  In  doing  this  it  must  be  borne  in  mind  that 
equivalent  quantities  replace  one  another;  that,  for  instance,  two  atoms  of  a 
univalent  element  are  required  to  replace  one  atom  of  a  bivalent  element, 
as,  for  instance,  in  the  case  of  the  decomposition  taking  place  between 
potassium  iodide  and  mercuric  chloride,  when  two  molecules  of  the 
first  are  required  to  decompose  one  molecule  of  the  second  compound  : 

K  —  I          rr  /Cl           TJ-  /I  K  —  Cl 

K-I    +    Hg\Cl  :       Hg\I  K-C1 
or 

2KI    +    HgCl2  =    HgI2    +  2KC1. 

Whenever  the  exchange  of  atoms  takes  place  between  univalent 
and  trivalent  elements,  three  of  the  first  are  required  for  one  of  the 
second,  as  in  the  case  of  the  action  of  sodium  hydroxide  on  bismuth 
chloride  : 

Na  —  OH  /Cl  /OH  Na  —  Cl 

Na  —  OH  +    Bi—  Cl    ==    Bi—  OH    +    Na  —  Cl 
Na  —  OH  \C1  \OH  Na  —  Cl 

or 

3NaOH  +    BiCl3    =    Bi(OH)3    +    3NaCl. 

In  the  following  examples  of  double  decomposition  an  exchange 
takes  place  between  the  atoms  of  metallic  elements,  or  between  the 
metallic  elements  and  the  hydrogen.  The  student,  in  completing  the 
equations,  has  also  to  select  the  correct  quantity,  i.  e.,  the  correct 
number  of  molecules  of  the  factors  required  for  the  change.  The 
interrogation  marks  indicate  that  more  than  one  atom  or  one  molecule 
of  the  substance  is  needed  for  the  reaction. 

Na'  +  H'Cl  Cu"SO4         +  H/S  = 

H/S04  -f  K'(?)  Ba"Cl2          +  Na/SO4 

Ca"  +  H'Cl  (?)      =  Na/C03        +  H/SO4 

Fe"  +  H/S04       =  Bi"'(N03)3  +  K'OH  (?)  = 

H'Cl  -f  Ag'NOg      =  Ala///(S04)8  +  K'OH  (?)  =r 

Ca"Cl2  +Ag'N03(?)=  A1/"(S04)S  +  Ca"(OH)2(?)  = 

Bi'^CL,  +  Ag'NOat?)  =  Fe2"'Cl6       +  Ag'NO3  (?)  = 


Types  of  chemical  change.     There  are  four  principal  ways  in 
which  chemical  actions  take  place.     These  may  be  represented  by  the 


CHEMICAL  EQUATIONS,  TYPES  OF  CHEMICAL  CHANGE,  ETC.   113 

following  equations,  in  which  the  letters  stand  for  elements  or  groups 
of  elements : 

1.  A  -|-  B  =  AB  direct  combination  or  addition. 

2.  (a)  AB     =  A     +  B    i 

(6)  ABC  =  AB  -|-  C     >  simple  decomposition. 
(c)  ABC  =  AC  f  BCJ 

3.  AB  +  C      =--  CB  +  A  displacement, 

4.  AB  -f-  CD  —  AD  +  CB  double  decomposition  or  metathesis. 

The  following  concrete  examples  will  serve  to  illustrate  the  above 
types  of  change : 

1.  Mg  -f  O  =  MgO. 

When  magnesium  metal  is  heated  to  the  ignition  point  it  unites 
with  oxygen  of  the  air,  and  gives  a  white  ash  known  as  magnesium 
oxide. 

2.  (a)  HgO  =  Hg  +  O. 

Mercuric  oxide,  when  heated  to  a  sufficient  temperature,  decom- 
poses into  its  elements — mercury  and  oxygen. 

(6)  KC1O3  =  KC1  +  30. 

When  potassium  chlorate  is  heated  sufficiently  high  and  long  it  de- 
composes into  the  compound  potassium  chloride  and  the  element 
oxygen. 

(c)  CaCO3  =  CaO  +  CO2. 

When  calcium  carbonate  is  heated  to  redness  it  is  decomposed  into 
two  new  compounds — namely,  calcium  oxide  and  carbon  dioxide. 

3.  Fe  +  2HC1  =  FeCl2  +  2H. 

When  a  solution  of  hydrochloric  acid  is  poured  upon  some  iron,  a 
brisk  evolution  of  hydrogen  gas  takes  place ;  and  a  new  compound, 
ferrous  chloride,  remains  in  the  solution. 

Although  in  a  sense  there  is  a  displacement  of  one  element  by 
another  in  every  chemical  action  between  two  substances  in  which 
two  new  substances  result,  by  custom  the  term  displacement  is  used 
in  those  cases  where  the  element  displaced  is  left  in  the  free  or  uncom- 
bined  state. 

4.  HC1  +  AgNO3  ==  AgCl  +  HNO3. 

When  a  solution  of  hydrochloric  acid  is  added  to  a  solution  of 
silver  nitrate,  silver  chloride  is  obtained  as  a  white  precipitate,  and 
nitric  acid  is  left  in  solution.  This  type  of  change,  known  as  double 
decomposition  or  metathesis,  is  one  of  the  most  frequently  occurring 
kinds  of  chemical  change  in  analysis  and  chemical  industry. 

8 


114  PRINCIPLES  OF  CHEMISTRY. 

Reversible  actions  and  chemical  equilibrium.  Experimental  study 
has  shown  that  in  many  instances  a  chemical  action,  when  once  started,  runs 
to  completion,  that  is,  continues  until  the  substance,  or  one  of  two  substances, 
undergoing  change  is  used  up.  For  example,  when  a  piece  of  magnesium  is 
ignited  the  action  continues  until  all  the  metal  is  used  up,  or  the  oxygen  in 
the  supply  of  air  is  exhausted.  Moreover,  this  action  cannot  be  reversed,  that 
is,  made  to  proceed  in  the  opposite  manner,  no  matter  how  much  heat,  or  what 
degree  of  heat,  available  in  the  laboratory,  we  apply  to  the  magnesium  oxide. 
In  other  words,  we  cannot  decompose  the  latter  into  magnesium  element  and. 
oxygen  by  heat  alone. 

On  the  other  hand,  there  are  many  instances  in  which  chemical  action, 
under  a  given  set  of  conditions,  is  not  complete,  but  proceeds  to  a  certain  point 
beyond  which  the  products  formed  tend  to  act  in  a  reverse  manner,  and  repro- 
duce the  original  substance  or  substances.  Such  changes  are  known  as  revers- 
ible actions,  and  evidently,  while  the  conditions  are  maintained,  the  whole 
chemical  process  comes  apparently  to  a  standstill.  But  in  the  light  of  the 
kinetic-molecular  theory  of  matter  it  is  believed  that  action  is  constantly  going 
on,  although  there  is  no  progress  made  in  either  direction.  The  forward  action 
of  the  system  is  counterbalanced  by  the  reverse  action  which  proceeds  at  the 
same  speed,  and  thus  is  produced  a  condition  of  seeming  rest,  or  chemical  equi- 
librium. An  example  of  equilibrium  as  a  result  of  two  equal  and  opposite 
actions  is  the  case  of  a  liquid  in  a  closed  container.  At  a  definite  temperature, 
the  space  above  the  liquid  is  saturated  with  its  vapor  which  exerts  a  constant 
pressure.  Although  there  is  apparent  rest,  molecules  of  the  liquid  are  passing 
off  into  the  space  above  it,  while  vapor  molecules  are  flying  back  into  the 
liquid.  These  opposite  actions  finally  balance  each  other,  and  then  the  system 
is  in  equilibrium.  If  the  conditions  are  changed,  for  example,  by  a  rise  in 
temperature,  the  equilibrium  is  disturbed,  a  readjustment  and  new  equilibrium 
follow,  in  which  more  vapor  molecules  exist  in  the  space  above  the  liquid, 
and  a  higher  vapor  pressure  is  produced. 

Reversible  chemical  actions  are  represented  by  equations  which  differ  from 
the  ordinary  chemical  equations,  in  that  the  equality  sign  is  replaced  by  two 
oppositely  directed  arrows,  thus : 
*  AB  +  CD  7=1  AD  -f  CB. 

Such  an  equation  indicates  that  the  action  takes  place  in  two  directions,  for- 
ward and  backward,  and  when  equilibrium  has  been  reached  as  much  material 
continues  to  be  transformed  in  one  direction  as  in  the  reverse  direction. 

While  in  many  cases  the  action  is  reversible,  yet  it  runs  far  toward  comple- 
tion in  one  direction.  This  condition  may  be  represented  by  making  one  of 
the  arrows  heavier  than  the  other,  thus  : 

MN  -f  PR  ;i±  MR  +  PN. 

The  following  is  a  good  example  of  a  reversible  chemical  change.  If  finely 
divided  iron  and  water  vapor  be  heated  in  a  sealed  glass  tube  so  that  none  of 
the  products  can  escape,  a  state  of  equilibrium  will  result,  in  which  four  prod- 
ucts exist  in  the  tube — namely,  iron,  iron  oxide,  water  vapor,  and  hydrogen. 

3Fe  +  4H2O  7±  Fe3O4  -f  8H. 
This  means   that  at  the  equilibrium  stage  the  hydrogen  reduces  the  iron 


CHEMICAL  EQUATIONS,  TYPES  OF  CHEMICAL  CHANGE,  ETC.   115 

oxide  reversely  as  fast  as  the  iron  reduces  the  water  vapor  ill  the  forward 
direction. 

When  the  experiment  is  performed  in  the  same  manner  as  above,  with  iron 
oxide  and  hydrogen  sealed  in  the  tube  at  the  equilibrium  point,  the  same  kinds 
of  products  exist  as  in  the  first  case,  thus  : 

Fe3O4  +  8H  Til  3Fe  +  4H2O. 

Evidently  a  necessary  condition  for  maintaining  a  chemical  equilibrium  in 
any  reversible  action  is  the  keeping  intact  of  all  the  factors  taking  part.  If 
one  of  the  products  of  an  action  be  removed  from  the  field  of  action  as  fast  as 
it  is  formed,  we  might  reasonably  predict  that  the  action  would  proceed  to 
completion  in  the  direction  made  easiest  by  the  removal  of  such  product.  This 
is  exactly  what  happens,  as  may  be  shown  in  the  above  instances.  When  steam 
is  passed  over  highly  heated  iron  through  an  open  tube,  the  action  takes  place 
to  completion,  thus  : 

Fe3  +  4H20  =  Fe304  +  »H. 

The  hydrogen  is  swept  out  of  the  tube  and  away  from  contact  with  the  iron 
oxide  by  the  current  of  steam.  The  action  continues  until  all  the  iron  is 
exhausted. 

Conversely,  when  hydrogen  gas  is  passed  over  heated  iron  oxide  in  an  open 
tube,  the  action  runs  to  completion  reversely  thus  : 

Fe3O4  +  8H  =  3Fe  +  4H2O. 

The  current  of  hydrogen  sweeps  the  water  vapor  (steam)  out  of  the  tube  as  fast 
as  it  is  produced.  The  action  continues  until  all  the  iron  oxide  is  exhausted 
by  conversion  to  elementary  iron. 

If  one  considered  only  the  first  action  he  would  conclude  that  iron  has  a 
greater  affinity  for  oxygen  than  hydrogen  has,  whereas  if  he  considered  only 
the  second  action,  he  would  say  that  hydrogen  has  a  greater  affinity  for  oxygen 
than  iron  has,  which  apparently  is  a  contradiction.  But  both  conclusions  are 
correct,  depending  on  circumstances.  In  fact,  in  reversible  actions  affinity 
plays  a  minor  part  in  determining  which  direction  a  chemical  change  will 
take,  this  being  controlled  in  largest  measure  by  the  physical  conditions  of  the 
experiment,  which  have  nothing  to  do  with  affinity.  This  is  admirably  shown 
by  the  following  example  :  When  common  salt  (sodium  chloride,  NaCl)  is  dis- 
solved in  20  per  cent,  aqueous  solution  of  sulphuric  acid  (H2SO4),  nothing 
apparently  happens  except  solution  of  the  salt.  Yet  a  reversible  action  takes 
place,  thus : 

2NaCl  +  H2SO4  7=1  Na2SO4  -f  2HC1. 

Four  products  are  present  in  solution  in  equilibrium.  When,  however,  con- 
centrated sulphuric  acid,  which  is  about  95  per  cent.,  is  -poured  upon  salt,  a 
brisk  evolution  of  hydrochloric  acid  gas  takes  place,  because  of  the  fact  that  it 
is  nearly  insoluble  in  concentrated  sulphuric  acid.  One  of  the  factors  in  the 
equilibrium  equation  above  is  thus  removed  from  the  field  of  action,  which 
thus  allows  the  action  to  go  forward  nearly  to  completion  and  leaves  the'im- 
pression  that  the  sulphuric  acid  has  a  greater  affinity  for  the  metal  sodium  than 
has  the  hydrochloric  acid,  or,  as  it  is  put  sometimes  in  text-books,  that  sul- 
phuric acid  is  a  "  stronger  "  acid  than  hydrochloric,  which,  in  fact,  is  not  true. 


116  PRINCIPLES  OF  CHEMISTRY. 

On  the  other  hand,  when  hydrochloric  acid  gas  is  passed  into  a  saturated 
aqueous  solution  of  sodium  sulphate  until  no  more  is  absorbed,  nearly  all  of 
the  sodium  is  precipitated  as  sodium  chloride,  because  the  latter  is  almost 
insoluble  in  concentrated  hydrochloric  acid  solution,  and  sulphuric  acid  is 
liberated  and  remains  in  the  solution.  In  this  case  one  of  the  factors  in  the 
above  equilibrium  equation  is  practically  removed  from  the  field  of  action  by 
precipitation,  thus  allowing  the  reverse  action  to  proceed  nearly  to  completion, 
and  leaving  the  impression  that  hydrochloric  acid  is  a  "stronger"  acid  than 
sulphuric. 

Mass  action.  The  vigor  and  extent  of  a  chemical  action  depends  upon 
the  freedom  with  which  the  molecules  can  clash  as  well  as  upon  the  affinity 
between  substances.  Hence  it  is  found  that  chemical  action  is  aided  far  better 
in  homogeneous  mixtures,  as  when  the  substances  are  present  in  the  gaseous 
state  or  in  solution.  Such  physical  systems  as  gas  arid  solid,  gas  and  liquid, 
liquid  and  solid,  solid  and  solid,  offer  only  limited  contact  between  molecules, 
and,  therefore,  more  or  less  impede  chemical  change.  In  homogeneous  mix- 
tures, in  the  case  of  reversible  actions,  the  proportion  of  the  substances  changed 
chemically  is  different  in  different  cases.  The  range  extends  all  the  way  from 
slight  change  to  nearly  complete  change.  But  in  each  individual  case  the 
amount  of  transformation  is  found  to  depend  upon  the  concentration  of  each 
substance  as  well  as  upon  the  affinity  between  the  substances.  This  is  often 
called  the  Law  of  Mass  Action,  which  may  be  stated  thus :  The  amount  of  a 
chemical  change  taking  place  in  a  given  lime  will  be  dependent  upon  the  molecular 
concentration  of  each  substance. 

In  chemical  operations  it  is  usually  desirable  to  obtain  one  or  other  of  the 
products  of  a  chemical  change  in  as  large  a  yield  as  possible.  If  the  action 
employed  is  a  non-reversible  one,  little  difficulty  will  be  experienced  in  obtain- 
ing a  full  yield.  In  reversible  actions,  according  to  the  law  of  mass  action, 
the  amount  of  the  new  product  formed  can  be  increased  in  two  ways,  either 
(1)  by  increasing  the  concentration  of  one  or  the  other  of  the  reacting  sub- 
stances, or  (2)  by  removing  one  or  the  other  of  the  products  formed.  The 
second  method — namely,  the  removal  of  one  of  the  products  of  the  action,  thus 
affecting  the  equilibrium  of  the  system  in  such  a  way  that  the  action  tends 
toward  completion — is  the  more  effective  way  of  increasing  the  yield.  This  is 
most  conveniently  done  by  selecting  such  actions  that  automatically  remove 
one  of  the  products  of  the  system  in  the  form  of  an  escaping  gas  or  an  insol- 
uble body  (precipitate1). 

As  instances  of  the  removal  of  one  of  the  products,  and,  therefore,  more  or 
less  complete  action,  may  be  mentioned  the  formation  of  all  the  hundreds  of 
insoluble  metallic  salts  which  are  produced  by  the  action  of  one  salt  solution 
upon  another  salt  solution,  the  first  solution  containing  a  metal  which,  with  the 
acid  of  the  second  solution,  may  form  an  insoluble  compound,  which  is  then 
invariably  produced  as  a  precipitate.  For  instance:  Calcium  carbonate, 
CaCO3,  is  insoluble ;  if  we  bring  together  two  solutions  containing  a  soluble 
calcium  salt  and  a  soluble  carbonate,  such  as  calcium  chloride,  CaCl2,  and 
sodium  carbonate,  Na2CO3,  calcium  carbonate  is  precipitated. 

1  The  term  precipitate  is  used  to  designate  an  insoluble  substance  which  separates  by  chem- 
ical action  in  a  liquid,  while  sediment  is  applied  to  the  collection  of  insoluble  matter  that  may 
be  floating  in  a  liquid,  and  does  not  imply  chemical  action. 


CHEMICAL  EQUATIONS,  TYPES  OF  CHEMICAL  CHANGE,  ETC.   117 

Examples  of  complete  action  because  of  the  removal  of  one  of  the  products 
as  a  gas  are:  Action  of  any  acid  on  any  carbonate,  whereby  carbon  dioxide 
gas  is  liberated ;  action  of  caustic  alkalies,  lime  or  magnesia,  on  ammonium 
salts,  whereby  ammonia  gas  is  liberated. 

Acids.  The  many  compounds  formed  by  the  union  of  elements 
are  so  various  in  their  nature,  that  no  system  of  classification  pro- 
posed up  to  the  present  time  can  be  called  perfect.  There  are,  how- 
ever, a  few  groups  or  classes  of  compounds,  the  properties  of  which 
are  so  well  marked,  that  a  substance  belonging  to  either  of  them  may 
be  easily  recognized.  These  groups  are  the  acids,  bases,  and  neutral 
substances. 

The  term  acid  is  applied  to  those  compounds  of  hydrogen  with  an 
electro-negative  element  or  group  of  elements  which  are  character- 
ized by  the  following  properties : 

1.  The  hydrogen  present  is  replaceable  by  metals,  the  compound 
thus  formed  being  a  salt. 

2.  They  change  the  color  of  many  organic  substances.     Thus, 
litmus,  a  coloring-matter  obtained  from   certain   lichens,  is  changed 
from  blue  to  red. 

3.  They  have  (when  soluble  in  water)  usually  an  acid  or  sour  taste. 

The  great  majority  of  acids  are  the  result  of  union  between  water  and  the 
oxides  of  those  elements  which  are  devoid  of  characteristic  metallic  properties. 
We  might,  therefore,  classify  non-metallic  elements  as  acid-forming  elements. 
There  are  a  few  exceptional  metals  which  form  a  series  of  oxides,  some  of 
which,  when  united  with  water,  give  acids;  for  example,  chromic  acid,  H2CrO4, 
permanganic  acid,  HMnO4.  The  formation  of  acids  from  oxides  is  shown  by 
the  following  equations : 

SO3      -f     H20    =     H2SO4. 

Sulphur  Sulphuric 

trioxide.  acid. 

P205      -f      3H2O        :    2H3P04. 

Phosphorus  Phosphoric 

pentoxide.  acid. 

C02       +       H2O      =      H2C03. 

Carbon  Carbonic 

dioxide.  acid. 

Evidently  in  the  acids  containing  oxygen,  often  called  oxyacids,  the  hydrogen 
is  derived  from  the  water  molecules  with  which  the  acidic  oxides  unite.  Those 
oxides  which  unite  with  water  to  give  acids  are  called  acidic  oxides  or  acid 
anhydrides.  As  was  said  before,  the  great  majority  of  acidic  oxides  are  derived 
from  the  non-metals,  but  there  are  some  oxides  of  the  non-metals  which  do  not 
form  acids,  for  example,  carbon  monoxide,  CO,  and  nitrogen  monoxide,  N7O. 

A  few  acids  contain  no  oxygen,  and  these  are  sometimes  called  hydracids. 
They  have  no  corresponding  oxides  and  are  combinations  of  hydrogen  with 
non-metallic  elements,  or  groups  of  elements  called  radicals.  The  principal 
ones  are  hvdrochloric  acid,  HC1,  hydrobromic  acid,  HBr,  hydriodic  acid,  HI, 


118  PRINCIPLES  OF  CHEMISTRY. 

hydrofluoric  acid,  HF,  or  H2F2,  hydrogen  sulphide,  H2S,  hydrocyanic  acid, 
H(CN>. 

However  much  the  acids  may  differ  in  certain  properties,  such  as  consist- 
ency, that  is,  whether  solid,  liquid,  or  gas,  solubility  in  water,  degree  of  acid 
taste  and  action  on  litmus  paper,  corrosiveness  to  organic  matter,  such  as  skin, 
wood,  cloth,  etc.,  they  are  all  alike  in  one  respect,  namely,  in  containing  hy- 
drogen which  is  separable  from  the  rest  of  the  molecule,  and  replaceable  by 
metals,  either  by  direct  action  of  a  metal  on  the  acid,  as  when  zinc  acts  on  a 
solution  of  sulphuric  or  hydrochloric  acid,  or  in  a  round-about  way.  There 
seems  to  be  a  strong  tendency  to  separation  between  the  hydrogen  and  the  rest 
of  the  molecule  of  an  acid  which  remains  intact  as  a  unit. 

According  to  the  number  of  hydrogen  atoms  replaceable  by  metals,  we  dis- 
tinguish monobasic,  dibasic,  and  tribasic  acids.  Hydrochloric  acid,  HC1,  is  a 
monobasic ;  sulphuric  acid,  H2SO4,  is  a  dibasic ;  phosphoric  acid,  H3PO4,  is  a 
tribasic  acid. 

Many  of  the  acids  sold  in  trade,  as  well  as  the  reagents  used  in  the  labora- 
tory, are  solutions  of  acids  in  water.  It  is  customary  to  call  these  solutions 
by  the  names  given  to  the  acids  themselves. 

Bases  or  basic  substances  show  properties  which  are  chemically 
opposite  to  those  of  acids.  As  a  general  rule  bases  are  compounds 
of  electro-positive  elements  (metals)  with  oxygen  (oxides)  or  more 
generally  with  oxygen  and  hydrogen  (hydroxides).  Thus,  silver 
oxide,  Ag2O,  and  sodium  hydroxide,  NaOH,  are  basic  substances. 
Other  properties  characteristic  of  bases  are : 

1.  When    acted  upon    by  acids,  they  form  salts ;    for    instance, 
when  sodium  hydroxide  and  nitric  acid  are  brought  together  water 
and  the  salt  sodium  nitrate  are  formed : 

NaOH  +  HN03  =  H2O  +  NaNO3. 

2.  They  have  (when  soluble  in  water)  an  alkaline  reaction,  i.  e., 
they  restore  the  color  of  organic  substances  when  previously  changed 
by  acids :  for  instance,  that  of  litmus,  from  red  to  blue. 

3.  They  have  (when  soluble  in  water)  the  taste  of  lye,  or  an  alka- 
line taste. 

The  term  base  was  originally  applied  to  the  metallic  oxides,  because  when 
salts  of  the  metals  were  highly  heated  they  were  decomposed,  leaving  a  non- 
volatile calx  or  ash,  the  oxide  of  the  metal,  while  the  acid  radical  of  the  salt 
was  driven  off.  Thus  the  metallic  oxides  were  regarded  as  the  base  or  stable 
groundwork  of  the  salts.  In  the  present-day  classification,  metallic  hydroxides 
are  called  bases,  but  as  the  oxides  bear  such  a  close  relationship  to  the  hy- 
droxides, in  fact,  many  of  them  being  converted  into  hydroxides  in  contact 
with  water,  many  authors  also  include  metallic  oxides  in  the  class  of  bases. 
The  relationship  between  metallic  oxides  and  hydroxides  is  well  shown  in  the 
case  of  quick-lime,  calcium  oxide.  Nearly  everyone  is  familiar  with  the 
process  of  slaking  lime  by  adding  water  to  quick-lime.  The  action  takes 
place  thus,  CaO  +  HaO  =  Ca(OH)2.  The  slaked  lime,  Ca(OH)2,  is  a 


CHEMICAL  EQUATIONS,  TYPES  OF  CHEMICAL  CHANGE,  ETC  119 

hydroxide  of  calcium.     The  relation  might  be  made  more  striking  by  writing 
the  formula  thus,  CaO  •  H2O. 

Some  oxides  do  not  unite  with  water  to  form  hydroxides,  but,  as  far  as  they 
are  acted  upon  by  acids,  they  give  the  same  end  product  (a  salt)  as  the  hy- 
droxides do,  as  may  be  illustrated  in  the  following  reactions : 

ZnO  '+  H2S04  ==  ZnSO4  +  H2O. 
Zn(OH)2  +  H2SO4  =  ZnSO4  +  2H2O. 

It  should  be  noted  that  one  of  the  products  that  is  always  formed  when  an 
acid  acts  on  a  metallic  hydroxide,  or  oxide,  is  water.  This  is  shown  in  the 
above  reactions. 

The  hydroxides  evidently  are  compounds  derived  from  water  by  the  re- 
placement of  part  of  the  hydrogen  in  the  water  molecule  by  metal,  thus 
leaving  the  radical,  (OH),  which  is  known  as  hydroxyl,  in  combination  with 
metal.  Hence,  these  compounds  are  called  hydroxides.  In  a  few  cases  hy- 
droxides can  be  obtained  by  the  direct  action  of  the  metals  on  water,  the  dis- 
placed hydrogen  escaping  as  a  gas.  This  seems  to  be  good  evidence  of  the 
relationship  between  the  hydroxides  and  water.  Most  metals,  however,  do  not 
act  on  water,  and  their  hydroxides  are  obtained  in  an  indirect  way.  (See 
Remarks  on  Tests  for  Metals,  in  the  chapter  on  Magnesium.) 

There  are  some  hydroxides  of  radicals  which  can  unite  with  acids  just  as 
the  metallic  hydroxides  do,  and  these  are  also  classed  as  basic  substances.  In 
them  the  radical  plays  the  part  of  a  metal. 

Most  of  the  metallic  oxides  and  hydroxides  are  practically  insoluble  in 
water,  and  therefore  have  no  appreciable  action  on  litmus  paper  and  no  taste. 
Hence,  alkaline  action  and  taste  are  not  a  sure  criterion  of  a  basic  substance. 
But  the  hydroxides  insoluble  in  water  can  act  on  acids  and  replace  their  hy- 
drogen by  metal,  just  as  the  soluble  hydroxides  do. 

The  hydroxides  differ  very  much  in  regard  to  specific  properties,  such  as 
solubility  in  water,  color,  taste,  etc.,  but  there  is  one  feature  common  to  all  of 
them,  namely,  the  presence  of  the  hydroxyl  group,  which  is  responsible  for 
the  class  properties  upon  which  such  compounds  are  classified  as  basic  sub- 
stances. 

It  should  be  noted  that  there  appears  to  be  a  tendency  to  easy  separation 
between  the  metal  and  the  hydroxyl  radical  in  the  bases,  just  as  there  is  be- 
tween the  hydrogen  and  the  acid  radical  in  the  case  of  acids.  The  significance 
of  these  facts  will  appear  when  the  Ionic  Theory  is  discussed. 

Neutralization  is  the  term  applied  to  the  interaction  between 
acids  and  bases  with  the  result  that  both  acid  and  basic  properties, 
disappear — i.  e.,  are  neutralized. 

All  substances  which  are  acid  in  character  contain  hydrogen  as 
one  of  their  constituents.  This  hydrogen  can  readily  be  replaced  by 
metals,  for  instance  by  magnesium,  when  hydrogen  is  liberated. 
Not  all  substances  containing  hydrogen  behave  in  this  manner ;  for 
example,  magnesium  does  not  liberate  hydrogen  from  petroleum, 
olive  oil,  sugar,  etc.,  which  all  contain  hydrogen.  Hence  the  hydro- 
gen of  acids  must  be  in  a  peculiar  condition.  That  it  is  this  hydro- 


120  PRINCIPLES  OF  CHEMISTRY. 

gen,  and  the  peculiar  condition  in  which  it  is  present,  which  impart 
to  acids  their  peculiar  properties,  are  demonstrated  by  the  fact  that  the 
acid  properties  disappear  as  soon  as  the  hydrogen  is  replaced  by  a 
metal.  Thus,  the  acid  characteristics  of  hydrochloric  acid,  HC1, 
vanish  when  it  is  acted  on  by  sodium,  or  by  the  basic  substance 
caustic  soda  (sodium  hydroxide,  NaOH),  both  of  which  cause  a  re- 
placement of  the  acid  hydrogen  by  sodium.  These  actions  can  be 
represented  by  the  equations  : 

HC1     -f    Na  NaCl     +     H. 

HC1    +    NaOH  NaCl     -f     H2O. 

In  both  cases  sodium  chloride,  NaCl  (common  salt),  is  formed,  which 
possesses  neither  acid  nor  basic  properties. 

Neutral  substances.  All  substances  having  neither  acid  nor  basic 
properties  are  neutral.  Water,  for  instance,  is  a  neutral  substance, 
having  no  acid  or  alkaline  taste,  and  no  action  on  red  or  blue  litmus. 
Many  neutral  substances,  to  some  extent  even  water,  appear  to  possess 
the  characteristic  properties  of  both  classes,  acids  and  bases ;  of  neither 
class,  however,  to  a  very  great  extent. 

Salts.  Salts  are  acids  in  which  hydrogen  has  been  replaced  by 
metals  or  by  basic  radicals.  There  are  several  general  methods  by 
which  salts  may  be  obtained : 

1.  By  the  action  of  an  acid  on  a  metal.     This  is  illustrated  in  the 
preparation  of  hydrogen  from   sulphuric  or   hydrochloric  acid   and 

zinc  or  iron. 

Zn  +  H2S04  =  ZnS04  +  H2. 
Fe  +  2HC1   =  FeCl2   +  H2. 

2.  By  the  action  of  an  acid  on  an  oxide  or  hydroxide  of  a  metal. 
This  is  of  wider  application  than  the  previous  method. 

ZnO  +  H2SO4  =  ZnSO4  +  H20. 
MgO  +  2HC1  =  MgCl2  -f  H2O. 
NaOH  +  HC1  =  NaCl  +  H2O. 

3.  By  the  action  of  an  acid  on  a  salt  of  a  volatile  acid.     This  finds 
most  extensive  and  useful  application  in  the  case  of  carbonates,  which 
are  decomposed  by  nearly  all  other  acids,  and  are  found  ready-formed 
in  nature  or  can  be  easily  made. 

MgCOs  +  H.2S04  =  MgS04  +  H20  +  C02. 
CaC03  +  2HC1   =  CaCl2    +  H2O  +  CO2. 

Other  volatile  acids  whose  salts  are  decomposed  by  acids  are  sulphur- 
ous, nitrous,  hydrogen  sulphide,  hydrocyanic,  etc.  The  manufacture 


CHEMICAL  EQUATIONS,  TYPES  OF  CHEMICAL  CHANGE,  ETC.   121 

of  hydrochloric  and  nitric  acids  by  the  aid  of  concentrated  sulphuric 
acid  is  an  example  of  the  method,  and  large  quantities  of  sodium 
sulphate  are  obtained  as  a  by-product  for  the  market. 

4.  By  the  action  of  one  salt  upon  another  salt.  This  method  is 
chiefly  used  when  one  of  the  products  is  insoluble  or  very  nearly  so, 
and  is  known  as  precipitation.  Usually  the  insoluble  product  is  the 
desired  one,  but  the  soluble  one  may  also  be  isolated.  A  great  many 
of  the  analytical  reactions,  called  tests,  fall  under  this  method. 
Nearly  all  carbonates  and  phosphates  are  obtained  by  precipitation. 

CaCl2  +  Na2CO3     =  CaC03     +  2NaCl. 
CaCl2  +  Na2HPO,  =  CaHP04  +  2NaCl. 

Calcium  carbonate  and  phosphate  are  precipitated  and  may  be  re- 
moved. 

An  example  of  the  use  of  the  method  to  get  the  soluble  product  is 
shown  by  the  equation  : 

CuS04  +  BaCl2  =  BaS04  +  CuCl,. 

A  solution  of  copper  chloride  is  obtained  by  filtering  off  the  barium 
sulphate. 

In  the  case  of  certain  salts  it  is  simpler  or  more  economic  to 
follow  special  methods,  which  may  be  seen  under  the  respective  salts. 
Some  of  these  salts  are  ferrous  iodide,  ammonium  iodide,  sodium 
hypochlorite,  iodide,  and  thiosulphate,  potassium  permanganate, 
dichromate  and  chlorate,  sodium  carbonate,  mercurous  and  mercuric 
chloride,  etc. 

According  to  the  number  of  hydrogen  atoms  replaced  in  an  acid, 
we  distinguish  normal  and  acid  salts.  A  normal  salt  is  one  formed  by 
the  replacement  of  all  the  replaceable  hydrogen  atoms  of  an  acid. 
For  instance :  Potassium  chloride,  KC1,  potassium  sulphate,  K2SO4, 
potassium  phosphate,  K3PO4.  (As  monobasic  acids  have  but  one  atom 
of  hydrogen  which  can  be  replaced,  they  form  normal  salts  only.) 

Normal  salts  often  have  a  neutral  reaction  to  litmus,  but  they  may 
have  an  acid  or  even  an  alkaline  reaction. 

It  is  found  that  soluble  normal  salts  derived  from  a  weakly  ioniz- 
ing acid,  as  carbonic,  boric,  phosphoric,  sulphurous,  hypochlorous, 
silicic,  hydrogen  sulphide,  and  a  strongly  ionizing  base,  as  sodium 
and  potassium  hydroxide,  and  some  others,  have  an  alkaline  reaction, 
while  those  derived  from  a  strongly  ionizing  acid  and  a  weakly  ioniz- 
ing base,  as  the  hydroxide  of  many  of  the  heavy  metals,  such  as 
Fe(OH)2,  A1(OH)3,  Cu(OH)2,  etc.,  have  an  acid  reaction.  The  reason 


122  PRINCIPLES  OF  CHEMISTRY. 

for  this  is  that  such  salts  are  partially  decomposed  or  hydrolyzed  by 
water.     Thus,  in  the  case  of  ferrous  sulphate, 

FeS04  -f  2H20  =  Fe(OH)2  +  H2SO4, 

the  small  quantity  of  free  acid  formed  affects  litmus-paper,  Fe(OH)2 
being  neutral.     Sodium  carbonate  is  acted  on  thus  : 

Na2C03  +  H20  =  NaHC03  +  NaOH, 

the  free  alkali  causes  litmus  to  turn  blue,  while  NaHCO3  is  neutral. 

Acid  salts  are  acids  in  which  there  has  been  replaced  only  a  portion 
of  their  replaceable  hydrogen  atoms.  For  instance  :  KHSO4,  K2H  PO4, 
KH2PO4.  While  acid  salts  have  generally  an  acid  reaction  to  litmus, 
there  are  many  exceptions  to  this  rule.  Indeed,  the  reaction  may  be 
neutral  or  even  alkaline,  as,  for  instance,  in  the  case  of  the  ordinary 
sodium  phosphate,  Na2HPO4,  which  is  slightly  alkaline  to  litmus. 

Basic  salts  are  salts  containing  a  higher  proportion  of  a  base  than 
is  necessary  for  the  formation  of  a  normal  salt.  Instances  are  basic 
mercuric  sulphate,  HgSO4.(HgO)2,  basic  lead  nitrate,  Pb(NO3)2. 
Pb(OH)2.  According  to  modern  views  basic  salts  are  looked  upon 
as  derived  from  bases  by  replacement  of  part  of  their  hydrogen  by  acid 
radicals.  In  the  base  lead  hydroxide,  Pb(OH)2,  one  of  the  hydrogen 
atoms  may  be  replaced  by  the  radical  of  nitric  acid,  when  basic  lead 

nitrate,  Pb<TT3'  is  formed. 


In  bismuth  hydroxide,  Bi(OH)3,  one,  two,  or  three  hydrogen  atoms 
may  be  replaced  by  nitric  acid,  when  the  salts  Bi(^  /QTT\ 


and  Bi(NO3)3  are  formed.     The  first  two  compounds  are  basic  salts, 
while  the  third  one  is  the  normal  salt. 

Double  salts  are  salts  formed  by  replacement  of  hydrogen  in  an 
acid  by  more  than  one  metal.  For  instance  :  Potassium-sodium  sul- 
phate, KNaSO4. 

Residue,  radical,  or  compound  radical,  are  expressions  for  un- 
saturated  groups  of  atoms  known  to  enter  as  a  whole  into  different 
compounds,  but  having  no  separate  existence.  For  instance:  The 
bivalent  oxygen  combines  with  two  atoms  of  the  univalent  hydrogen, 
forming  the  saturated  compound  H2O,  water.  If  we  take  from  this 
H2O  one  atom  of  H,  there  is  left  the  group  of  atoms  HO  (generally 
written  OH),  consisting  of  an  atom  of  oxygen  in  which  but  one  point 
of  attraction  is  actually  saturated,  the  second  one  not  being  pro- 
vided for. 

This  group,  OH,  is  a  residue  or  radical,  and  is  known  to  enter  into 


CHEMICAL  EQUATIONS,  TYPES  OF  CHEMICAL  CHANGE,  ETC.  123 

many  compounds ;  it  is,  for  instance,  a  constituent  of  all  the  different 
hydroxides  (formerly  called  hydrates),  such  as  potassium  hydroxide, 
KOH,  calcium  hydroxide,  Ca(OH)2,  etc. 

According  to  the  number  of  points  of  attraction  left  unprovided 
for  in  a  radical,  we  distinguish  univalent,  bivalent,  trivalent,  and 
quadrivalent  radicals. 

Carbon  is  a  quadrivalent  element  forming  with  the  univalent  hy- 
drogen the  saturated  compound  CH4.  By  removal  of  one,  two,  or 
three  hydrogen  atoms  the  radicals  CH3',  CH/',  CH'",  are  formed. 

Constitutional  or  graphic  formulas.  Though  it  is  impossible 
to  examine  the  structure  of  a  molecule  by  means  of  a  microscope,  yet 
we  may  obtain  some  information  of  the  atomic  arrangement  within 
the  molecules  by  a  study  of  the  formation  and  decomposition  which 
they  undergo  under  different  conditions. 

Such  investigations  lead  to  the  conclusion  that  molecules  are  not 
merely  clusters  of  atoms  held  together  irregularly,  but  that  the 
atoms  are  arranged  systematically  and  occupy  a  definite  position 
within  the  molecules  of  each  individual  substance. 

In  order  to  represent  figuratively  our  views  regarding  the  atomic 
arrangement  the  so-called  constitutional  or  graphic  formulas  are  often 
used.  Thus,  while  sulphuric  acid  is  represented  by  the  molecular 
formula  H2SO4,  we  may  assign  to  it  the  graphic  formula  SO/'. (OH)2, 
which  indicates  that  sulphuric  acid  is  made  up  of  the  bivalent  radi- 
cal SO2  and  of  two  univalent  radicals  OH.  In  order  to  give  a  yet 
fuller  expression  of  our  views  regarding  the  linkage  of  the  atoms,  sul- 
phuric acid  may  be  graphically  represented  thus : 


O— H 


01          vv, 

-H 


QUESTIONS. — What  are  chemical  equations  and  how  do  they  serve  as  a  basis 
for  calculations?  Mention  the  principal  types  of  chemical  change,  with  exam- 
ples. Define  reversible  actions  and  chemical  equilibrium.  How  may  a  revers- 
ible action  be  made  to  run  to  completion  in  one  direction?  Give  an  example. 
What  is  the  law  of  mass  action?  Define  an  acid,  and  state  the  general  proper? 
ties  of  basic  and  neutral  substances.  By  what  means  can  they  be  recognized? 
Distinguish  between  mono-,  di-,  and  tri-basic  acids.  What  are  salts  and  how 
are  they  formed?  Define  neutral,  acid,  and  double  salts.  Explain  the  term 
radical  or  residue. 


124  PRINCIPLES  OF  CHEMISTRY. 

In  these  formulas  we  show  that  sulphur  exerts  the  valence  of  six, 
that  four  of  its  affinities  are  saturated  by  oxygen,  while  the  two  re- 
maining are  attached  to  two  oxygen  atoms,  the  unsaturated  affinities 
of  which  are  satisfied  by  hydrogen. 

9.  GENERAL  REMARKS  REGARDING  ELEMENTS. 

Relative  importance  of  different  elements.  Of  the  total 
number  of  about  seventy-six  elements,  comparatively  few  (about 
one-fourth)  are  of  great  and  general  importance  for  the  earth,  and  the 
phenomena  taking  place  upon  it.  These  important  elements  form 
the  greater  part  of  the  mass  of  the  solid  portion  of  the  earth,  and  of 
the  water  and  atmosphere,  and  of  all  animal  and  vegetable  matter. 

Another  number  of  elements  are  of  less  importance,  because  either 
they  are  not  found  in  any  large  quantity,  or  do  not  take  any  active 
or  essential  part  in  the  formation  of  organic  matter ;  yet  they  are  of 
interest  and  importance  on  account  of  being  used,  in  their  elementary 
state  or  in  the  form  of  different  compounds,  in  every-day  life  for 
various  purposes. 

A  third  number  of  elements  are  found  in  such  minute  quantities 
in  nature  that  they  are  almost  exclusively  of  scientific  interest.  Even 
the  existence  of  some  elements,  the  discovery  of  which  has  been 
claimed,  is  doubtful. 

The  elements  enumerated  in  column  I.  are  those  of  great  and  gen- 
eral interest ;  in  II.  those  claiming  interest  on  account  of  the  special 
use  made  of  them ;  in  III.  those  having  scientific  interest  chiefly. 

I.  II. 


Aluminum  Antimony  Iridiuin 

Calcium  Arsenic  Lead 

Carbon  Barium  Lithium 

Chlorine  Bismuth  Manganese 

Hydrogen  Boron  Mercury 

Iron  Bromine  Molybdenum 

Magnesium  Cadmium  Nickel 

Nitrogen  Cerium  Platinum 

Oxygen  Chromium  Radium 

Phosphorus  Cobalt  Silver 

Potassium  Copper  Strontium 

Silicon  Fluorine  Tin 

Sodium  Gold  Uranium 

Sulphur  Iodine  Zinc 


GENERAL  REMARKS  REGARDING  ELEMENTS.      125 
III. 


Argon 

Neon 

Thallium 

Beryllium  (Glucinum) 

Osmium 

Thorium 

Caesium 

Palladium 

Thulium 

Columbium  (Niobium) 

Praseodymium 

Titanium 

Erbium 

Rhodium 

Tungsten 

Gadolinium 

Rubidium 

Vanadium 

Gallium 

Ruthenium 

Xenon 

Germanium 

Samarium 

Ytterbium 

Helium 

Scandium 

Yttrium 

Indium 

Selenium 

Zirconium 

Krypton 

Tantalum 

Lanthanum 

Tellurium 

Neodymium 

Terbium 

Classification  of  elements  may  be  based  upon  either  physical  or 
chemical  properties,  or  upon  a  consideration  of  both.  A  natural 
classification  of  all  elements  is  the  one  dividing  them  into  two  groups 
of  metals  and  non-rnetals. 

Metals  are  all  elements  which  have  that  peculiar  lustre  known  as 
metallic  lustre ;  which  are  good  conductors  of  heat  and  electricity  ; 
which,  in  combination  with  oxygen,  form  compounds  generally 
showing  basic  properties ;  and  which  are  capable  of  replacing  hy- 
drogen in  acids,  thus  forming  salts. 

Non-metals  or  metalloids  are  all  elements  not  having  the  above- 
mentioned  properties.  Their  oxides  in  combination  with  water  gen- 
erally have  acid  properties.  In  all  other  respects  the  chemical  and 
physical  properties  of  non-metals  differ  widely.  Their  number 
amounts  to  18,  the  other  58  elements  being  metals. 

Natural  groups  of  elements.  Besides  classifying  all  elements 
into  metals  and  non-metals,  certain  members  of  both  classes  exhibit 
so  much  resemblance  in  their  properties,  that  many  of  them  have 
been  arranged  into  natural  groups.  The  members  of  such  a  natural 
group  frequently  show  some  connection  between  atomic  weights  and 
properties. 

Chlorine,  35.2  Sulphur,  31.8  Lithium,  7.0  Calcium,  39.8 
Bromine,  79.3  Selenium,  78.6  Sodium,  22.9  Strontium,  86.9 
Iodine,  125.9  Tellurium,  126.6  Potassium,  38.8  Barium,  136.4 

Each  three  elements  mentioned  in  the  above  four  columns  resemble 
each  other  in  many  respects,  forming  a  natural  group.  The  relation 


126  PRINCIPLES  OF  CHEMISTRY. 

between  the  atomic  weights  will  hardly  be  suspected  by  looking  at 
the  figures,  but  will  be  noticed  at  once  by  adding  together  the  atomic 
weights  of  the  first  and  last  elements  and  dividing  this  sum  by  2, 
when  the  atomic  weights  (very  nearly,  at  least)  of  the  middle  mem- 
bers of  the  series  are  obtained.  Thus  : 
8S.2  +  125.9  _  go  55 .  31.8  +  126.6  __  79_2  .  7.0  +  38.8  =  22>g .  39.8  +  136.4  =  g8_L 

Mendelejeff's  periodic  law.1  The  relationship  between  atomic 
weights  and  properties  has  been  used  for  arranging  all  elements  sys- 
tematically in  such  a  manner  that  the  existing  relation  is  clearly 
pointed  out.  Of  the  various  schemes  proposed,  the  one  arranged  by 
Mendelejeff  may  be  selected  as  most  suitable  to  show  this  relation. 

Looking  at  Mendelejeff's  table  on  page  128  it  will  be  seen  that  all 
the  elements  are  arranged  in  the  order  of  their  atomic  weights,  and 
that  the  latter  increase  gradually  by  only  a  unit  or  a  few  units. 
Moreover,  the  arrangement  is  such  that  nine  groups  and  twelve 
series  are  formed.  The  remarkable  features  of  this  classification 
may  thus  be  stated  :  Elements  which  are  more  or  less  closely  allied 
in  their  physical  and  chemical  properties  are  made  to  stand  together 
in  a  group,  as  may  be  seen  by  pointing  out  a  few  of  the  more  gen- 
erally known  instances  as  found  in  the  groups  I.,  II.,  and  VII.,  the 
first  one  containing  the  alkali  metals,  the  second,  the  metals  of  the 
alkaline  earths,  the  last  the  halogens. 

There  is,  moreover,  to  be  noticed  a  periodic  repetition  in  the  prop- 
erties of  the  elements  arranged  in  the  horizontal  lines  from  left  to 
right.  Leaving  out  groups  0  and  VIII.  for  the  present,  we  find 
that  the  power  of  the  elements  to  combine  with  oxygen  atoms 
increases  regularly  from  the  left  to  the  right,  while  the  power  of  the 
elements  to  combine  with  hydrogen  atoms  increases  from  the  right  to 
the  left,  as  may  be  shown  by  the  following  instances : 

I.  II.  III.  IV.  V.  VI.  VII. 

N^O  MgO  A1203  SiO2  P2O5  SO3  ClaO7 

Hydrogen  compounds  unknown  SiH4  PHs  SH2  C1H 

The  oxides  on  the  left  show  strongly  basic  properties,  as  illustrated 
by  sodium  oxide  ;  these  basic  properties  become  weaker  in  the  second, 
and  still  weaker  in  the  third  group  ;  the  oxides  of  the  fourth  group 
show  either  indifferent,  or  but  slightly  acid  properties,  which  latter 
increase  gradually  in  the  fifth,  sixth,  and  seventh  groups. 

i  The  consideration  of  this  law  should  be  postponed  until  the  student  has  become  acquainted 
with  the  larger  number  of  important  elements. 


GENERAL  REMARKS  REGARDING   ELEMENTS.  127 

While  some  elements  show  an  exception,  it  may  be  stated  that 
most  of  the  elements  of  group  I.  are  univalent,  of  II.  bivalent,  of 
III.  trivalent,  of  IV.  quadrivalent,  of  V.  quinquivalent,  of  VI. 
sexivalent,  and  of  VII.  septivalent. 

Properties  other  than  those  above  mentioned  might  be  enumerated 
in  order  to  show  the  regular  gradation  which  exists  between  the 
members  of  the  various  series,  but  what  has  been  pointed  out  will 
suffice  to  prove  that  there  exists  a  regular  gradation  in.  the  properties 
of  the  elements  belonging  to  the  same  series,  and  that  the  same  change 
is  repeated  in  the  other  series,  or  that  the  changes  in  the  properties  of 
elements  are  periodic.  It  is  for  this  reason  that  a  series  of  elements 
is  called  a  period  (in  reality  a  small  period,  in  order  to  distinguish  it 
from  a  large  period,  an  explanation  of  which  term  will  be  given 
directly). 

The  12  series  or  periods  given  in  the  following  table  show  another 
highly  characteristic  feature,  which  consists  in  the  iact  that  the  corre- 
sponding members  of  the  even  (2, 4,  6,  etc.)  periods  and  of  the  uneven 
(3,  5,  7,  etc.)  periods  resemble  each  other  more  closely  than  the  mem- 
bers of  the  even  periods  resemble  those  of  the  uneven  periods.  Thus 
the  metals  calcium,  strontium,  and  barium,  of  the  even  periods,  4,  6, 
and  8,  resemble  each  other  more  closely  than  they  resemble  the  metals 
magnesium,  zinc,  and  cadmium,  of  the  uneven  periods,  3,  5,  and  7,  the 
latter  metals  again  resembling  each  other  greatly  in  many  respects. 

It  is  for  this  reason  that  in  the  table  the  elements  belonging  to  one 
group  are  not  placed  exactly  underneath  each  other,  but  are  divided 
into  two  lines  containing  the  members  of  even  and  uneven  periods 
separately,  whereby  the  elements  resembling  each  other  most  are 
made  to  stand  together. 

In  arranging  the  elements  by  the  method  indicated,  it  was  found 
that  the  elements  mentioned  in  group  VIII.  could  not  be  placed  in 
any  of  the  12  small  periods,  but  that  they  had  to  be  kept  separately 
in  a  group  by  themselves,  three  of  these  metals  always  forming  aL 
intermediate  series  following  the  even  periods  4,  6,  and  10. 

An  uneven  and  even  series,  together  with  an  intermediate  series, 
form  a  large  period,  the  number  of  elements  contained  in  a  complete 
large  period  being,  therefore,  8  +  8  +  3  =  19. 

An  apparently  objectionable  feature  is  the  incompleteness  of  the 
table,  many  places  being  left  blank  ;  but  it  is  this  very  point  which 
renders  the  table  so  highly  interesting  and  valuable. 

Mendelejeff,  in  arranging  his  scheme,  claimed  that  the  places  left 
blank  belonged  to  elements  not  yet  discovered,  and  he  predicted  not 
only  the  existence  of  these  as  yet  missing  elements,  but  also  described 


128 


PRINCIPLES  OF  CHEMISTRY. 


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GENERAL  REMARKS  REGARDING   ELEMENTS.  129 

their  properties.  Fortunately  his  predictions  have,  in  several  cases, 
been  verified,  a  number  of  the  missing  elements  having  since  been 
discovered.  Among  them  may  be  mentioned  scandium,  gallium,  and 
ycntianium.  These  elements  not  only  fitted  in  the  previously  blank 
spaces  by  virtue  of  their  atomic  weights,  but  their  general  properties 
also  assigned  to  them  the  places  which  they  now  occupy. 

When  the  table  was  first  arranged  it  did  not  show  group  0.  The 
elements  forming  this  group  have  all  been  discovered  since  the  year 
1894,  and  their  discovery  necessitated  the  addition  of  an  extra  group. 
In  order  to  avoid  renumbering  the  previously  known  groups  the  new 
group  was  designated  by  zero. 

Another  graphic  representation  of  the  periodic  law  is  obtained  by 
arranging  the  elements  according  to  the  increase  in  their  atomic 
weights  on  a  spiral  line,  as  shown  on  the  diagram  (Fig.  36). 
From  the  centre  of  the  spiral  extend  20  radii,  and  in  placing  the 
elements  on  the  intersections  of  the  spiral  and  a  radius  three  im- 
portant facts  are  noticed,  viz.  :  1.  The  distances  of  the  elements 
from  the  centre  of  the  spiral  are  proportionate  (or  nearly  so)  to 
their  atomic  weights.  2.  From  left  to  right  the  elements,  arranged 
on  the  diametric  lines,  follow  one  another  according  to  the  periodic 
grouping.  3.  The  elements  belonging  to  the  even  series  of  one  of 
the  groups  are  on  one  radius,  while  the  elements  belonging  to  the 
uneven  series  of  the  same  group  find  their  position  on  the  radius 
opposite.  For  example,  calcium,  strontium,  and  barium,  of  the 
even  series  4,  6,  and  8  of  group  II.,  are  on  a  radius  opposite  the 
one  on  which  we  find  magnesium,  zinc,  and  cadmium,  of  the  uneven 
series  3,  5,  and  7  of  group  II. 

Physical  properties  of  elements.  Most  elements  are,  at  the 
ordinary  temperature,  solid  substances,  two  are  liquids  (bromine  and 
mercury),  and  of  the  more  important  elements  five  are  gases  (oxy- 
gen, hydrogen,  nitrogen,  chlorine,  and  fluorine). 

Most,  if  not  all,  of  the  solid  elements  may  be  obtained  in  the  crys- 
tallized state;  a  few  are  amorphous  and  crystallized,  or  polymorphous. 
The  physical  properties  of  many  elements  in  these  different  states 
differ  widely.  For  instance :  Carbon  is  known  crystallized  as  diamond 
and  graphite,  or  amorphous  as  charcoal.  The  property  of  elements  to 
assume  such  different  conditions  is  called  allotropy,  and  the  different 
forms  of  an  element  are  termed  allotropic  modifications. 

Some  of  the  gaseous  elements  are  also  capable  of  existing  in  allo- 
tropic modifications  For  instance:  Oxygen  is  known  as  such  and  as 
ozone,  the  latter  differing  from  the  common  oxygen  both  in  its  physi- 
cal and  chemical  properties.  The  explanation  given  for  this  surprising 


130 


PRINCIPLES  OF  CHEMISTRY. 


fact,  that  one  and  the  same  element  has  different  properties  in  certain 
modifications,  is,  that  either  the  molecules  or  the  atoms  within  the 
molecules  are  arranged  differently.  Ozone,  for  instance,  has  three 
atoms  of  oxygen  in  the  molecule,  while  the  common  oxygen  molecule 
contains  but  two  atoms. 

Most  of  the  elements  are  tasteless  and  odorless ;  a  few,  however, 
have  a  distinct  odor  and  taste,  as,  for  instance,  iodine  and  bromine. 

FIG.  36. 


fu~ 


Diagram  of  periodic  system  in  spiral  form. 


Relationship  between  elements  and  the  compounds  formed 
by  their  union.  The  properties  of  the  compounds  formed  by  the 
combination  of  elements  are  so  various  that  it  is  next  to  impossible 
to  give  any  general  rule  by  which  they  may  be  indicated.  It  may 


GENERAL  REMARKS  REGARDING   ELEMENTS.  131 

be  said,  however,  that  nearly  all  of  the  gaseous  compounds  contain 
at  least  one  gaseous  element,  and  that  solid  elements,  when  combining 
with  each  other,  generally  form  solid  substances,  rarely  liquids,  and 
never  compounds  showing  the  gaseous  state  at  the  ordinary  tem- 
perature. 

Nomenclature.  The  chemical  nomenclature  of  compound  sub- 
stances has  undergone  considerable  changes  within  the  last  twenty- 
five  years.  These  changes  were  made  in  conformity  with  our  present 
views  of  the  constitution  of  the  compounds. 

Whenever  the  syllable  ide  is  used  to  replace  the  ending  of  a  non- 
metallic  element  it  designates  that  this  element  has  entered  into  com- 
bination with  another  element  or  with  a  radical.  Thus,  we  speak  of 
<>x/Vcs,  sulphicfos,  carbides,  chlorides,  etc.,  when  referring  to  compounds 
formed  by  the  union  of  oxygen,  sulphur,  carbon,  or  chlorine  with 
another  element  or  with  a  radical. 

When  two  elements  combine  in  one  proportion  only,  little  difficulty 
is  experienced  in  the  formation  of  a  name,  as,  for  instance,  in  iodide 
of  potassium  or  potassium  iodide,  KI,  chloride  of  sodium  or  sodium 
chloride,  NaCl. 

When  two  elements  combine  in  more  than  one  proportion,  the 
syllables,  mono,  di,  tri,  tetra,  and  penta  are  frequently  used  to  designate 
the  relative  quantity  of  the  elements.  For  instance :  Carbon  mon- 
oxide, CO,  carbon  dioxide,  CO2,  phosphorus  tfn'chloride,  PC13,  nitrogen 
t< '//-oxide,  N2O4,  phosphorus  £>entachloride,  PC15. 

In  many  cases  the  syllables  ous  and  ie  are  used  to  distinguish  the 
proportions  in  which  two  elements  combine ;  the  syllable  ous  being 
used  for  the  simpler  or  lower,  the  syllable  ic  for  the  more  complex  or 
higher  form  of  combination.  For  instance :  Phosphorous  chloride, 
PC13,  and  phosphoric  chloride,  PC15;  ferrous  oxide,  FeO,  ferric 
oxide,  Fe2O3. 

The  syllable  sesqui  is  used  occasionally  to  indicate  that  a  compound 
contains  one-half  more  of  an  element  than  another  compound  formed 
from  the  same  elements.  Thus,  ferric  chloride,  FeCl3,  is  sometimes 
called  sesgiiichloride  of  iron,  as  it  contains  one-half  more  of  chlorine 
than  does  ferrous  chloride,  FeCl2. 

The  syllables  proto  or  sub  and  per  have  also  been  used  as  prefixes 
to  differentiate  between  compounds  formed  by  the  same  elements. 
For  instance,  mercurous  chloride,  HgCl,  is  called  protochloMe  or 
sw6chloride,  while  mercuric  chloride,  HgCl2,  is  often  designated  as 
jwchloride  of  mercury. 

When  two  oxides  of  the  same  element  ending  in  ous  and  ic  form 


132  PRINCIPLES  OF  CHEMISTRY, 

acids  (by  entering  in  combination  with  water),  the  same  syllables  are 
used  to  distinguish  these  acids.  Phosphor<n*s  oxide,  P2O3,  forms 
phosphoroits  acid ;  phosphoric  oxide,  P2O5,  forms  phosphoric  acid. 

The  salts  formed  by  these  acids  are  distinguished  by  using  the  syl- 
lables lie  and  ate.  Phosphite  of  sodium  is  derived  from  phosphorous 
acid,  phosphate  of  sodium  from  phosphoric  acid.  Sulphites  and  sul- 
phates are  derived  from  sulphurous  and  sulphuric  acid,  respectively. 

When  an  element  forms  more  than  two  acids  the  syllables  hypo  and 
per  are  often  used  to  designate  the  nature  of  these  acids,  as  also  that 
of  their  respective  salts.  Hypo  is  prefixed  to  the  compound  contain- 
ing less  oxygen  than  the  ous  acid ;  and  per  is  prefixed  to  the  com- 
pound containing  more  oxygen  than  the  ic  acid.  For  instance,  hypo- 
chlorous  acid,  HC1O ;  chlorous  acid,  HC1O2 ;  chloric  acid,  HC1O< ; 
perchloric  acid,  HC1O4.  The  salts  formed  from  these  acids  are  called 
hypochlorites,  chlorites,  chlorates,  and  perchlorates. 

According  to  the  new  nomenclature,  the  name  of  the  metal  precedes 
that  of  the  acid  or  acid  radical  in  an  acid.  For  instance,  sodium 
phosphite,  instead  of  phosphite  of  sodium ;  potassium  sulphate,  instead 
of  sulphate  of  potassium.  The  acids  themselves  are  looked  upon  as 
hydrogen  salts,  and  are  sometimes  named  accordingly  :  hydrogen 
nitrate  for  nitric  acid,  hydrogen  chloride  for  hydrochloric  acid,  etc. 

When  the  number  of  elements  and  the  number  of  atoms  increase  in 
the  molecule,  the  names  become  in  most  cases  more  complicated.  The 
rules  applied  to  the  formation  of  such  complicated  names  will  be 
spoken  of  later. 

How  to  study  chemistry.  In  studying  chemistry,  the  student 
is  advised  to  impress  upon  his  memory  five  points  regarding  every 
important  element  or  compound.  These  points  are  : 

1.  Occurrence  in  nature.      Whether    in  free  or  combined    state; 
whether  in  the  air,  water,  or  solid  part  of  the  earth. 

2.  Mode  of  preparation  by  artificial  means. 

3.  Physical  properties.     State  of  aggregation  and  influence  of  heat 
upon  it ;  color,  odor,  taste,  solubility,  etc. 

4.  Chemical  properties.     Atomic  and  molecular  weight ;  valence  ; 
amount  of  attraction  toward   other  elements  or  compounds ;  acid, 
alkaline,  or  neutral  reaction ;  reactions  by  which  it  may  be  recog- 
nized and  distinguished  from  other  substances. 

5.  Application  and  use  made  of  it  in  e very-day  life,  in  the  arts, 
manufactures,  or  medicine. 

Of  the  most  important  elements  and  compounds,  the  history 


GENERAL  REMARKS  REGARDING  ELEMENTS.  133 

their   discovery,  and,  occasionally,  some    special  points  of  interest, 
should  be  noticed  also. 

"  All  students  having  the  facility  for  working  in  a  chemical  labora- 
tory are  strongly  advised  to  make  all  those  experiments  and  reactions 
which  will  be  mentioned  in  connection  with  the  different  substances 
to  be  considered  in  this  book. 

By  adopting  this  mode  of  studying  chemistry  the  student  will  soon 
acquire  a  fair  knowledge  of  chemical  facts,  yet  he  might  know  little 
of  the  science  of  chemistry.  In  order  to  acquire  this  latter  knowl- 
edge he  should  study  not  only  facts,  but  also  the  relationship  existing 
between  them  and  between  the  laws  governing  the  phenomena  con- 
nected with  these  facts.  It  is  by  this  method  only  that  the  science 
of  chemistry  can  be  successfully  mastered. 

QUESTIONS. — Why  are  not  all  the  elements  of  equal  importance?  State  the 
physical  and  chemical  properties  of  metals.  How  are  metals  distinguished 
from  non-metals  ?  What  relation  often  exists  between  the  atomic  weights  of 
elements  belonging  to  the  same  group?  Explain  the  term  allotropic  modifica- 
tion. Mention  some  elements  capable  of  existing  in  allotropic  modifications. 
What  relation  exists  between  the  properties  of  elements  and  the  properties  of 
the  compounds  formed  by  their  union  ?  In  which  cases  are  the  syllables  mono-, 
di-,  tri-,  tetra-,  and  penta-  used  in  chemical  nomenclature?  What  use  is  made 
of  the  syllables  ous  and  ic,  ite  and  ate,  in  distinguishing  compounds  from  each 
other?  What  are  the  principal  features  of  the  periodic  law? 


III. 

NON-METALS  AND  THEIR  COMBINATIONS. 


THE  total  number  of  the  non-metals  is  about  eighteen  ;  some  of 
them,  such  as  selenium,  tellurium,  argon,  helium,  and  a  few  others, 
are  of  so  little  importance  that  they  will  be  but  briefly  considered 
in  this  book. 


Symbols,  atomic  weights,  and  derivation  of  names. 


Boron,  B   =    10.9.    From  borax,  the  substance  from  which  boron  was  first 

obtained. 


Bromine,        Br  =    79.36.  From  the  Greek  fip&jios  (bromos),  stench,  in  allusion  to 
the  intolerable  odor. 

Carbon,          C    =    11.91.  From  the  Latin  carbo,  coal,  which  is  chiefly  carbon. 

Chlorine,        Cl  =    35.18.  From  the  Greek  ^Awpdf  (chloros),  green,  in  allusion  to  its 
green  color. 

Fluorine,        F  =    18.9.     From  fluorspar,  the  mineral  calcium  fluoride,  used  as  flux 
(fluo,  to  flow.) 

Hydrogen,     H  =       1.       From  the  Greek  v6up  (hudor),  water,  and  -yewdu  (gennao), 
to  generate. 

Iodine,  I    =  125.9.     From  the  Greek  lav  (ion),  violet,  referring  to  the  color  of 

its  vapors. 

Nitrogen,       N  =    13.93.  From  the  Greek  virpov  (nitron),  nitre,  and  -yewdo  (gen- 

nao),  to  generate. 
Oxygen,          O  =;    15.88.  From  the  Greek  ofvf  (oxus),  acid,  and  yevvdu  (gennao),  . 

to  generate. 
Phosphorus,  P  =    30.77.  From  the  Greek  0«f  (phos),  light,  and  tfpetv  (pherein),  to 

bear. 
Silicon,  Si  =    28.2.     From  the  Latin  silex,  flint,  or  silica,  the  oxide  of  silicon 

Sulphur,        S  =   31.83.   From  sal,  salt,  and  nvp  (pur),  fire,  referring  to  the  com- 
bustible properties  of  sulphur. 

135 


136  NON-METALS  AND  THEIR  COMBINATIONS. 

State  of  aggregation. 
Under  ordinary  conditions  the  non-metals  show  the  following  states: 

Gases.  Liquids.  Solids. 

B.   P.  B.   P.  F.   P.        B.  P. 

Hydrogen,     —253°  C.  Bromine,  64°  C.  Phosphorus,     44°  C.  280°  0. 

Oxygen,         —183  Iodine,  11          175 

Nitrogen,       —194  Sulphur,         114         400 

Chlorine,         -  33  Carbon,  |  Slightly  volatile 

Fluorine,       — 190  Boron,    >      in  electric 

Silicon,  )       furnace. 

Occurrence  in  nature. 

a.  In  a  free  or  combined  state. 

Carbon  in  coal,  organic  matter,  carbon  dioxide,  carbonates. 
Nitrogen  in  air,  ammonia,  nitrates,  organic  matter. 
Oxygen  in  air,  water,  organic  matter,  most  minerals. 
Sulphur  chiefly  as  sulphates  and  sulphides. 

b.  In  combination  only. 
Boron  in  boric  acid  and  borax. 

Bromine  in  salt  wells  and  sea-water  as  magnesium  bromide,  etc. 
Chlorine  as  sodium  chloride  in  sea-water,  etc. 
Fluorine  as  calcium  fluoride,  fluorspar. 
Hydrogen  in  water  and  organic  matter. 
Iodine  as  iodides  in  sea-water. 

Phosphorus  as  phosphate  of  calcium,  iron,  etc.,  in  bones  and  rocks. 
Silicon  as  silicic  acid  or  silica,  and  in  silicates. 

Time  of  discovery. 

Sulphur,  )  Long  known  in  the  elementary  state  ;  recognized  as  elements  in  the 

Carbon,    /     latter  part  of  the  eighteenth  century. 

Phosphorus,  1669,  by  Brandt,  of  Germany. 

Chlorine,  1774,  by  Scheele,  of  Sweden. 

Nitrogen,  1772,  by  Kutherford,  of  England. 

Oxygen,  1773,  by  Scheele,  of  Sweden  ;  1774,  by  Priestley,  of  England. 

Hydrogen,  1766,  by  Cavendish,  of  England. 

Boron,  1808,  by  Gay-Lussac,  of  France. 

Fluorine,  1810,  by  Ampere,  of  France 

Iodine,  1812,  by  Courtois,  of  France. 

Silicon,  1823,  by  Berzelius,  of  Sweden. 

Valence.1 

Univalent.  Bivalent.  Trivalent  or  quinquivalent.       Quadrivalent. 

Hydrogen,  Oxygen,  Nitrogen,  Carbon, 

Chlorine,  Sulphur.  Boron,  Silicon. 

Bromine,  Phosphorus. 

Iodine, 
Fluorine. 

1  The  valences  here  given  are  the  ones  generally  exerted  by  the  elements,  but  it  will  be 
shown  later  that  most  of  the  elements  may  exhibit  a  valence  differing  from  the  ones  here 
mentioned. 


OXYGEN.  137 

10.    OXYGEN.1 

O"  =  15.88. 

History.  Oxygen  was  discovered  in  the  year  1773  by  Scheele,  in 
Sweden,  and  one  year  later  by  Priestley,  in  England,  independently 
of  each  other ;  its  true  nature  was  soon  afterward  recognized  by  La- 
voisier, of  France,  who  gave  it  the  name  oxygen,  from  the  two  Greek 
words,  oc^c  (oxtis),  acid,  and  ysvvda)  (gennao),  to  produce  or  generate. 
Oxygen  means,  consequently,  generator  of  acids. 

Occurrence  in  nature.  There  is  no  other  element  on  our  earth 
present  in  so  large  a  quantity  as  oxygen.  It  has  been  calculated  that 
not  less  than  about  one-third,  possibly  as  much  as  45  per  cent.,  of  the 
total  weight  of  our  earth  is  made  up  of  oxygen ;  it  is  found  in  a  free 
or  uncombined  state  in  the  atmosphere,  of  which  it  forms  about  one- 
fifth  of  the  weight.  Water  contains  eight-ninths  of  its  weight  of 
oxygen,  and  most  of  the  rocks  and  different  mineral  constituents  of 
our  earth  contain  oxygen  in  quantities  varying  from  30  to  50  per 
cent. ;  finally,  it  is  found  as  one  of  the  common  constituents  of  most 
animal  and  vegetable  matters. 

If  the  unknown  interior  of  our  earth  should  be  similar  in  composition  to  the 
solid  crust  of  mineral  constituents  which  have  been  analyzed,  then  the  sub- 
joined table  will  give  approximately  the  proportions  of  those  elements  present 
in  the  largest  quantity. 

Oxygen       .  .  .45  parts.  Calcium  .  .  .4  parts. 

Silicon        .  .  .     28     "  Magnesium  .  .     2     " 

Aluminum  .               8     "  Sodium   .  .  .     2     " 

Iron  .         .  .               6     "  Potassium  .  .     2     " 

Preparation.  The  oxides  of  the  so-called  noble  metals  (gold, 
silver,  mercury,  platinum)  are  by  heat  easily  decomposed  into  the 
metal  and  oxygen : 

HgO=  Hg  +  O; 
Ag,0=2Ag  +  O. 

A  more  economical  method  of  obtaining  oxygen  is  the  decomposi- 
tion of  potassium  chlorate,  KC1O3,  into  potassium  chloride,  KC1, 
and  oxygen  by  application  of  heat : 

KC1O3  =  KC1  +  3O. 

While  the  above  formula  represents  the  final  result  of  the  decomposition,  it 
1  Many  instructors  prefer  to  postpone  the  discussion  of  the  laws  of  combination,  atomic 
theory,  symbols,  and  chemical  equations  until  after  a  few  elements  and  compounds  have  been 
studied  as  an  introduction  and  foundation.  If  such  a  procedure  is  followed  by  those  who  use 
this  book,  the  equations  in  the  chapters  that  may  be  taken  up  before  the  theoretical  matters 
are  presented  which  make  the  equations  intelligible,  should,  of  course,  be  omitted.  They 
are  given  in  each  chapter  for  the  sake  of  completeness  and  reference. 


138  NON-METALS  AND   THEIR   COMBINATIONS. 

takes  place  actually  in  two  stages.  At  first  potassium  chlorate  gives  up  but 
one-fifth  of  its  total  oxygen,  forming  potassium  chloride  and  perchlorate, 
KC104,  thus : 

5KC1O3  =  3KC1O,  +  2KC1  +  3O. 

This  part  of  the  decomposition  takes  place  at  a  comparatively  low  temper- 
ature ;  after  it  is  complete,  the  temperature  rises  considerably  and  the  decom- 
position of  the  perchlorate  begins  : 

KC1O4  =  KC1  +  4O. 

If  the  potassium  chlorate  be  mixed  with  30-50  per  cent,  of  man- 
ganese dioxide,  and  this  mixture  be  heated,  the  liberation  of  oxygen 
takes  place  with  greater  facility  and  at  a  lower  temperature  than  by 
heating  potassium  chlorate  alone.  Apparently,  the  manganese  dioxide 
takes  no  active  part  in  the  decomposition,  as  its  total  amount  is  found 
in  an  unaltered  condition  after  all  potassium  chlorate  has  been  decom- 
posed by  heat.  A  satisfactory  explanation  regarding  this  action  of 
manganese  dioxide  is  yet  wanting. 

A  third  method  is  to  heat  to  redness,  in  an  iron  vessel,  manganese 
dioxide  (MnO2),  which  suffers  then  a  partial  decomposition : 
3MnO2  =  MngO4  -f  2O. 

In  this  case  there  is  liberated  but  one-third  of  the  total  amount  of 
oxygen  present,  while  two-thirds  remain  in  combination  with  the 
manganese. 

Other  methods  of  obtaining  oxygen  are :  Decomposition  of  water  by  elec- 
tricity, heating  of  dichromates,  nitrates,  barium  dioxide,  and  other  substances, 
which  evolve  a  portion  of  the  oxygen  contained  in  the  molecules. 

Heating  a  concentrated  solution  of  bleaching  powder  with  a  small  quantity 
of  a  cobalt  salt  (cobaltous  chloride)  furnishes  a  liberal  supply  of  oxygen,  the 
calcium  hypochlorite  of  the  bleaching  powder  being  decomposed  into  calcium 
chloride  and  oxygen : 

Ca(ClO)2  =  CaCl2  +  2O. 

Oxygen  may  be  obtained  at  the  ordinary  temperature  by  adding  water  to  a 
mixture  of  powdered  potassium  ferricyanide  and  barium  dioxide,  and  also  by 
the  decomposition  of  potassium  permanganate  and  hydrogen  dioxide  in  the 
presence  of  dilute  sulphuric  acid. 

A  commercial  method  operated  largely  in  England  is  Erin's  process,  which 
consists  in  pumping  purified  air  under  pressure  over  barium  oxide  contained 
in  a  tube  and  heated  to  about  700°  C.,  whereby  barium  dioxide  is  formed.  The 
accumulated  nitrogen  of  the  air  escapes  by  a  valve  from  the  end  of  the  tube. 
When  formation  of  barium  dioxide  is  complete,  the  air-supply  is  cut  off  and 
the  pump  is  reversed,  thus  producing  a  partial  vacuum  in  the  tube.  Under 
this  condition,  although  the  same  temperature  is  maintained  as  before,  the 


OXYGEN.  139 

barium  dioxide  decomposes  into  barium  oxide  and  oxygen,  which  latter  is 
pumped  away  and  stored  in  tanks.  Oxygen  of  about  96  per  cent,  is  obtained. 
The  changes  taking  place  in  the  two  stages  are  represented  thus : 

BaO   +   O   =   BaO2; 


This  process  is  a  good  example  of  the  kind  of  change  known  as  Reversible 
Action  (see  page  114).  When  the  dioxide  is  exhausted,  the  process  is  re- 
peated. One  kilogram  of  barium  oxide  yields  about  ten  liters  of  oxygen  at  a 
single  operation. 

The  quantity  of  oxygen  liberated  from  a  given  quantity  of  a  substance  may 
be  easily  calculated  from  the  atomic  and  molecular  weights  of  the  substance 
or  substances  suffering  decomposition.  For  instance :  100  pounds  of  oxygen 
may  be  obtained  from  how  many  pounds  of  potassium  chlorate,  or  from  how 
many  pounds  of  manganese  dioxide?  (See  page  100.) 

The  molecular  weight  of  potassium  chlorate  is  found  by  adding  together 
the  weights  of  1  atom  of  potassium  =  38.86  +  1  atom  of  chlorine  —  35.18  +  3 
atoms  of  oxygen  =  47.64;  total  =  121.68.  Every  121.68  parts  by  weight  of 
potassium  chlorate  liberate  the  weight  of  3  atoms,  or  47.64  parts  by  weight,  of 
oxygen.  If  47.64  are  obtained  from  121.68,  100  are  obtained  from  255.4. 

47.64  :  121.68  :  :  100  :  x 

x  =  255.4. 

In  a  similar  manner,  it  will  be  found  that  815.7  pounds  of  manganese  dioxide 
are  necessary  to  produce  100  pounds  of  oxygen.  Mn02  =  54.6  -4-  31.76  =  86.36. 
3Mn02  =  3  X  86.36  =  259.08.  Every  259.08  parts  furnish  2  x  15.88  =  31.76 
parts  of  oxygen. 

31.76  :  259.08  :  :  100  :  x 

*  =  815.7, 

The  density  of  a  gas  is  the  weight  of  1  liter.  To  find  what  volume  corre- 
sponds to  a  given  weight  of  a  gas,  divide  the  weight  by  the  density.  The  den- 
sity of  oxygen  is  1.429  grammes  in  1  liter  at  0°  C.  and  760  mm.  pressure. 
Hence,  under  these  conditions,  100  grammes  of  oxygen  would  measure  100  -*- 
1.429  =  69.979  liters.  (For  method  of  calculating  gas  volumes  under  other  than 
standard  conditions  of  temperature  and  pressure,  see  article  on  Gas  Analysis.) 

The  densities  of  gases  are  generally  given  in  books,  but  they  can  be  calcu- 
lated, if  the  molecular  weights  of  the  gases  are  known.  The  relation  between 
densities  and  molecular  weights  of  gases  is  discussed  on  page  108.  The  density 
of  any  gas  is  equal  to  the  density  of  hydrogen  multiplied  by  one-half  the 
molecular  weight  of  the  gas ;  1  liter  of  hydrogen  at  0°  C.  and  760  mm.  pressure 
weighs  0.08987  gramme,  the  molecular  weight  of  oxygen  is  31.76;  hence  1  liter 
of  oxygen  weighs  0.08987  X  15.88  =  1.427  grammes. 

Experiment  1.  Generate  oxygen  by  heating  a  small  quantity  (about  £ 
grammes)  of  potassium  chlorate  in  a  dry  flask  of  about  100  c.c.  capacity,  to 
which,  by  means  of  a  perforated  cork,  a  bent  glass  tube  has  been  attached, 
which  leads  under  the  surface  of  water  contained  in  a  dish  (Fig.  37).  Collect 
the  gas  by  placing  over  the  delivery-tube  large  test-tubes  (or  other  suitable  ves- 


140 


NON-METALS  AND  THEIR   COMBINATIONS. 


sels)  filled  with  water.  Notice  that  a  strip  of  wood,  a  wax  candle,  or  any  other 
substance  which  burns  in  air.  burns  with  greater  energy  in  oxygen,  and  that 
an  extinguished  taper,  on  which  a  spark  yet  remains,  is  rekindled  when  placed 
in  oxygen  gas.  Notice,  also,  the  physical  properties  of  the  gas.  If  the  decompo- 
sition has  been  too  rapid  by  using  too  large  a  flame,  the  gas  will  appear  cloudy, 
due  to  the  dragging  over  of  some  of  the  contents  of  the  flask  by  it.  The  cloud 
will  disappear  upon  standing. 

CAUTION.  In  all  experiments  of  this  kind,  where  a  vessel  is  filled  wiih  a  hot  gas, 
the  exit  tube  should  be  removed  from  water  before  removing  the  flame,  to  prevent  water 
from  being  drawn  back  into  the  vessel  as  the  gas  cools  and  contracts. 

Experiment  2.  In  a  porcelain  crucible  held  in  a  pipe-stem  triangle,  place  a 
layer  of  potassium  chlorate  about  J  inch  deep.  Heat  moderately  at  first  until 


Apparatus  for  generating  oxygen. 

frothing  ceases,  and  then  gradually  to  low  red  heat.  Cool  and  dissolve  the 
residue  in  a  little  water  in  the  crucible,  warming  to  hasten  solution.  Taste  the 
solution.  Does  it  taste  like  common  salt  (sodium  chloride)?  Compare  with 
the  taste  of  potassium  chlorate.  Pour  some  of  the  solution  into  a  test-tube  and 
add  a  few  drops  of  a  solution  of  silver  nitrate.  Do  the  same  with  a  solution  of 
common  salt.  The  white  clotted  substance,  known  as  a  precipitate,  is  silver 
chloride,  and  is  given  by  all  soluble  chlorides.  Also  add  some  silver  nitrate 
solution  to  a  solution  of  a  little  potassium  chlorate.  Is  any  precipitate  formed? 
All  chlorates  are  soluble. 

Physical  properties.  Oxygen  is  a  colorless,  inodorous,  tasteless 
gas,  slightly  heavier  than  air.  Under  a  pressure  of  50  atmospheres, 
and  at  a  temperature  of  -118°  C.  (-180.4°  F.)  it  condenses  to  a 
transparent,  pale-bluish  liquid,  which  under  ordinary  atmospheric 
pressure  boils  at  -183°  C.  (-297.4°  F.).  Its  absolute  boiling-point, 
above  which  it  cannot  be  condensed  to  a  liquid  by  any  pressure,  no 
matter  how  high,  is -118°  C.  (-180.4°  F.). 


OXYGEN.  141 

For  practical,  including  medical,  purposes  oxygen  is  sold  stored  in 
strong  steel  cylinders,  the  gas  being  condensed  by  a  pressure,  gen- 
erally, of  225  pounds  to  about  -fa  of  its  volume. 

The  temperature  above  which  a  gas  cannot  be  liquified  by  pressure  is 
known  as  its  critical  temperature.  The  failure  of  former  attempts  to  liquefy 
oxygen  and  a  few  other  gases  was  due  to  the  fact  that,  though  an  enormous 
pressure  was  used,  the  gas  was  not  brought  to  the  critical  temperature. 

Oxygen  is  but  sparingly  soluble  in  water  (about  3  volumes  in  100 
at  common  temperature).  A  liter  of  oxygen  under  760  mm.  pressure, 
and  at  the  temperature  of  0°  C.  (32°  F.),  weighs  1.429  grammes. 

Chemical  properties.  The  principal  feature  of  oxygen  is  its  great 
affinity  for  almost  all  other  elements,  both  metals  and  non-metals; 
with  nearly  all  of  which  it  combines  in  a  direct  manner.  The  more 
important  elements  with  which  oxygen  does  not  combine  directly  are  : 
Cl,  Br,  I,  F,  Au,  Ag,  and  Pt;  but  even  with  these  it  combines  in- 
directly, excepting  F. 

The  act  of  combination  between  other  substances  and  oxygen  is 
called  oxidation,  and  the  products  formed,  oxides.  The  large  number 
of  oxides  are  divided  usually  into  three  groups,  and  distinguished  as 
basic  oxides  (sodium  oxide,  Na2O,  calcium  oxide,  CaO),  neutral  oxides 
(water,  H2O,  manganese  dioxide,  MnO2,  lead  dioxide,  PbO2),  and 
acid-forming  or  acidic  oxides,  also  called  anhydrides  (carbon  dioxide, 
CO2,  sulphur  trioxide,  SO3).  Whenever  the  heat  generated  by  oxida- 
tion (or  by  any  other  chemical  action)  is  sufficient  to  cause  the  emis- 
sion of  light,  the  process  is  called  combustion.  Oxygen  is  the  chief 
supporter  of  all  the  ordinary  phenomena  of  combustion.  Substances 
which  burn  in  atmospheric  air  burn  with  greater  facility  in  pure 
oxygen.  This  property  is  taken  advantage  of  to  recognize  and  dis- 
tinguish oxygen  from  most  other  gases.  Processes  of  oxidation  evolv- 
ing no  light  are  called  slow  combustion.  An  instance  of  slow  combus- 
tion is  the  combustion  of  the  different  organic  substances  in  the  living 
animal,  the  oxygen  being  supplied  by  respiration. 

In  some  cases  the  heat  generated  by  the  slow  combustion  of  a  sub- 
stance may  raise  its  temperature  sufficiently  high  to  cause  ignition, 
which  is  then  called  spontaneous  combustion.  Thus,  greasy  rags  or  wet 
hay,  when  piled  in  heaps,  may  ignite  spontaneously,  because  some  oils 
and  damp  hay  undergo  slow  oxidation,  which  raises  the  temperature. 

For  a  process  of  oxidation  it  is  not  absolutely  necessary  that  free 
oxygen  be  present.  Many  substances  contain  oxygen  in  such  a  form 
of  combination  that  they  part  with  it  easily  when  brought  in  contact 
with  substances  having  a  greater  affinity  for  it.  Such  substances  are 


142  NON-METALS  AND    THEIR   COMBINATIONS. 

called  oxidizing  agents,  as,  for  instance,  nitric  acid,  potassium  chlorate, 
potassium  permanganate,  etc. 

In  all  combustions  we  have  at  least  two  substances  acting  chemically  upon 
one  another,  which  substances  are  generally  spoken  of  as  combustible  bodies 
and  supporters  of  combustion.  Illuminating  gas  is  a  combustible  substance, 
and  oxygen  a  supporter  of  combustion ;  but  these  terms  are  only  relatively 
correct,  since  oxygen  may  be  caused  to  burn  in  illuminating  gas,  whereby  it  is 
made  to  assume  the  position  of  a  combustible  substance,  while  illuminating  gas 
is  the  supporter  of  combustion. 

While  some  substances,  such  as  iron  and  phosphorus,  undergo  slow  combus- 
tion at  the  ordinary  temperature,  there  is  a  certain  degree  of  temperature, 
characteristic  of  each  substance,  at  which  it  inflames.  This  point  is  known  as 
kindling  temperature,  and  varies  widely  in  different  substances.  Zinc  ethyl 
ignites  at  the  ordinary  temperature,  phosphorus  at  50°  C.  (122°  F.),  sulphur  at 
about  450°  C.  (842°  F.},  carbon  at  a  red  heat,  and  iron  at  a  white  heat.  The 
heat  produced  by  the  combustion  is  generally  higher  than  the  kindling  tem- 
perature, and  it  is  for  this  reason  that  a  substance  continues  to  burn  until  it  is 
consumed,  provided  the  supply  of  oxygen  be  not  cut  off,  and  the  temperature 
be  not  through  some  cause  lowered  below  the  kindling  temperature. 

The  total  amount  of  heat  evolved  during  the  combustion  of  a  substance  is 
the  same  as  that  generated  by  the  same  substance  when  undergoing  slow  com- 
bustion, but  the  intensity  depends  upon  the  time  required  for  the  oxidation. 
A  piece  of  iron  may  require  years  to  combine  with  oxygen,  and  it  may  be 
burned  up  in  a  few  minutes ;  yet  the  total  heat  generated  in  both  cases  is  the 
same,  though  we  can  notice  and  measure  it  in  the  first  instance  by  most  deli- 
cate instruments  only,  while  in  the  second  it  is  very  intense. 

While  heat  is  evolved  when  two  or  more  elements  combine  chemically,  heat 
is  absorbed  when  decomposition  takes  place.  In  fact,  the  quantities  of  heat 
evolved  and  absorbed  by  combining  and  decomposing  identical  quantities  of 
matter  are  absolutely  alike.  Thus,  heat  is  evolved  when  mercury  and  oxygen 
combine,  but  the  same  quantity  of  heat  .is  absorbed  when  the  mercuric  oxide 
thus  formed  is  decomposed  into  its  elements  by  the  action  of  heat. 

Whenever  a  substance  has  the  power  to  unite  with  others,  it  can  do  chemical 
work ;  it  possesses  chemical  energy.  Consequently,  all  combustible  substances 
can  do  work  ;  i.  e.,  by  combining  with  oxygen  they  evolve  heat,  which  in  turn 
may  be  transformed  into  motion  or  into  some  other  form  of  energy. 

The  chief  supply  of  chemical  energy  at  our  disposal  is  derived  from  plant- 
life.  All  kinds  of  wood,  and  its  decomposition-product,  coal,  possess  chemical 
energy.  This  energy  is  stored  up  in  vegetable  matter,  because  the  sun's  heat 
caused  a  decomposition  of  water  and  carbon  dioxide,  which  substances  are  the 
two  chief  compounds  used  in  the  construction  of  plant  tissue.  In  burning 
vegetable  matter  the  oxygen  removed  from  the  water  and  carbon  dioxide  by 
the  action  of  the  sun's  rays  is  taken  up  again,  and  heat  is  evolved. 

Ozone  is  an  allotropic  modification  of  oxygen,  which  is  formed 
when  non-luminous  electric  discharges  pass  through  atmospheric  air 
or  through  oxygen ;  when  phosphorus,  partially  covered  with  water, 


OXYGEN.  143 

is  exposed  to  air,  and  also  during  a  number  of  chemical  decomposi- 
tions. Ozone  differs  from  ordinary  oxygen  by  possessing  a  peculiar 
odor,  by  being  an  even  stronger  oxidizing  agent  than  common  oxygen, 
by  liberating  iodine  from  potassium  iodide,  etc.  This  latter  action 
may  be  used  for  demonstrating  the  presence  of  ozone  by  suspending 
in  the  gas  a  paper  moistened  with  a  solution  of  potassium  iodide  and 
starch.  The  iodine,  liberated  by  the  ozone,  forms  with  starch  a  dark- 
blue  compound.  Theoretically,  we  assume  that  ozone  contains  three, 
common  oxygen  but  two,  atoms  in  the  molecule,  which  is  substan- 
tiated by  the  fact  that  three  volumes  suffer  a  condensation  to  two 
volumes  when  converted  into  ozone,  which  would  indicate  that  three 
molecules  of  oxygen  furnish  two  molecules  of  ozone,  thus  : 


302  =  203;  or  3  [O  =  O]  =2 


[A] 


Ozone  is  obtained  in  a  pure  condition  by  passing  the  impure  gas  through  a 
tube  cooled  by  liquid  oxygen.  It  is  then  a  blue  liquid  which  boils  at  — 110°  C. 
( — 166°  F.),  forming  a  blue  gas.  Atmospheric  air,  in  which  part  of  the  oxygen 
has  been  converted  into  ozone  by  the  electrical  method,  is  used  for  bleaching 
purposes,  purification  of  starch,  resinifying  oils,  purifying  water  of  germs  and 
organic  matter,  etc. 

Ozone  occurs  in  small  quantities  in  country  air,  but  is  rarely  noticed  in 
cities,  where  it  is  decomposed  too  quickly  by  the  impurities  of  the  atmospheric 
air.  It  has  been  assumed  that  ozone  acts  advantageously,  as  it  has  a  tendency 
to  destroy  matters  which  are  unwholesome.  Too  little,  however,  is  known  of 
the  subject  to  justify  a  positive  opinion  in  regard  to  it. 

Thermo-chemistry.  It  is  stated  in  Chapter  5  that  the  free  or  available 
chemical  energy  in  a  chemical  change  usually  appears  as  heat.  This  heat  can 
be  measured  in  calories  in  an  apparatus  called  a  calorimeter  (see  page  48). 
The  equations  ordinarily  used  to  represent  chemical  changes  do  not  express 
energy  changes,  but  simply  what  kinds  of  substances  are  concerned  in  the 
change,  and  what  new  substances  are  formed.  For  example,  the  expression, 
2H  -}-  O  =  H2O,  when  translated  means  that  when  hydrogen  and  oxygen  unite 
water  is  formed,  but  it  says  nothing  about  the  fact  that  a  great  amount  of  chem- 
ical energy  is  liberated  as  heat.  Likewise  the  expression,  HgO  =  Hg  +  O, 
which  means  that  when  mercuric  oxide  undergoes  decomposition  (by  heat) 
mercury  and  oxygen  are  formed,  says  nothing  about  the  fact  that  during  the 
change,  heat  energy  is  "absorbed  and  transformed  into  chemical  energy.  For 
the  purpose  of  showing  the  energy  change  involved,  use  is  made  of  thermal 
equations.  The  amount  of  heat  energy  in  calories  represented  in  thermal  equa- 
tions as  liberated  or  absorbed  refers  to  certain  weights  of  the  substances  in- 
volved in  the  chemical  change.  These  weights  are  the  number  of  grammes  cor- 
responding to  the  chemical  symbols  of  the  substances.  For  instance,  the  thermal 
equation  for  the  formation  of  water  is  written,  2H  +  O  =  H2O  +  67,883  cal., 
which  means  that  when  2  grammes  of  hydrogen  unite  with  15.88  grammes  of 
oxygen  to  form  17.88  grammes  of  water  (corresponding  to  the  symbol  H2O), 


144  NON-METALS  AND   THEIR   COMBINATIONS. 

67,883  calories  of  heat  are  liberated,  or  enough  to  raise  nearly  68  kilogrammes 
of  water  one  degree  in  temperature.  The  thermal  equation, 

HgO  =  Hg  -t  O  —  30,370.5  cal., 

means  that  when  214.38  grammes  of  oxide  of  mercury  (corresponding  to  HgO) 
are  decomposed  by  heat  into  mercury  and  oxygen,  30,370.5  calories  of  heat 
are  absorbed  and  converted  into  chemical  energy  which  is  associated  with  the 
elements  mercury  and  oxygen.  •  The  plus  sign  is  used  when  heat  is  liberated  in 
the  formation  of  a  compound,  and  the  latter  is  termed  exothermic;  while  the 
minus  sign  indicates  absorption  of  heat,  and  the  compound  is  termed  endother- 
mic.  Exothermic  compounds  are  relatively  stable,  while  endothermic  ones  are 
unstable  and  often  explosive.  They  decompose  easily  with  liberation  of  heat. 

Ozone  is  endothermic,  as  heat  is  absorbed  during  its  formation  from  oxygen. 
When  it  decomposes  heat  is  liberated.  The  thermal  equation,  2O3  —  3O2  + 
64,314  cal.,  states  that  when  95.28  grammes  of  ozone  (corresponding  to  2O3) 
decomposes  into  ordinary  oxygen,  64,314  calories  of  heat  are  liberated.  The 
greater  chemical  energy  of  ozone  over  that  of  oxygen  accounts  for  its  greater 
chemical  activity  as  compared  with  oxygen. 

Thermo-chemical  measurements  are  of  great  importance  in  several  practical 
directions;  for  example,  for  determining  the  fuel  values  of  samples  of  coal, 
coke,  wood,  fuel  values  of  articles  of  food  in  the  field  of  physiology,  etc. 

11.    HYDROGEN.    WATER.    HYDROGEN  DIOXIDE. 
H  =  1.  H2O  =  17.88.  H2O2  =  33.76. 

History.  Hydrogen  was  obtained  by  Paracelsus  in  the  16th  cen- 
tury ;  its  elementary  nature  was  recognized  by  Cavendish,  in  1766. 
The  name  is  derived  from  Mvp  (hudor),  water,  and  yewfo  (gennao),  to 
generate,  in  allusion  to  the  formation  of  water  by  the  combustion  of 
hydrogen. 

Occurrence  in  nature.  Hydrogen  is  found  chiefly  as  a  component 
element  of  water ;  it  enters  into  the  composition  of  most  animal  and 
vegetable  substances,  and  is  a  constituent  of  all  acids.  Small  quanti- 
ties of  free  hydrogen  are  found  in  the  gases  produced  by  the  decom- 
position of  organic  matters  (as,  for  instance,  in  the  intestinal  gases), 
and  also  in  the  natural  gas  escaping  from  the  interior  of  the  earth. 

QUESTIONS. — By  whom  and  at  what  time  was  oxyge'n  discovered?  How  is 
oxygen  found  in  nature?  Mention  three  processes  by  which  oxygen  may  be 
obtained.  How  much  oxygen  may  be  obtained  from  490  grammes  of  potas- 
sium chlorate?  State  the  physical  and  chemical  properties  of  oxygen.  Ex- 
plain the  terms  combustion,  slow  combustion,  combustible  substance,  and  sup- 
porter of  combustion.  Mention  some  oxidizing  agents.  What  is  ozone,  and 
how  does  it  differ  from  common  oxygen?  Under  what  circumstances  is  ozone 
formed?  What  is  thermo-chemistry ?  What  is  a  thermal  reaction? 


HYDROGEN.  145 

Preparation.  Hydrogen  may  be  obtained  by  passing  an  electric 
current  through  water  previously  acidified  with  sulphuric  acid,  by 
which  it  is  decomposed  into  its  elements  : 

H2O  =  2H  +  O. 

A  second  process  is  the  decomposition  of  water  by  metals.  Some 
metals,  such  as  potassium  and  sodium,  decompose  water  at  the  ordi- 
nary temperature ;  while  others,  iron,  for  instance,  decompose  it  at  a 

red  heat : 

K   +  H,0    ==  KOH  +  H  ; 
3Fe  +  4H20  =  FesO4  +   8H. 

A  very  convenient  way  of  liberating  hydrogen  is  the  decomposition 
of  dilute  hydrochloric  or  sulphuric  acid  by  zinc  or  iron : 

Zn  +  2HC1    =  ZnCl2  +  2H; 

Zinc 
chloride. 

Fe  +  H2S04  =  FeSO,  +  2H. 
Ferrous 
sulphate. 

Hydrogen  may  also  be  obtained  by  heating  granulated  zinc  or 
aluminum  with  strong  solutions  of  potassium  or  sodium  hydroxide, 
in  which  case  the  decomposition  is  explained  thus : 

Zn  -f  2KOH    ==  K2ZnO2    -f  2H; 

Potassium 
zincate. 

Al  +  3NaOH  =  Na3AlO3  +  3H. 

Sodium 
aluminate. 

Whenever  hydrogen  is  generated,  care  should  be  taken  to  expel  all 
atmospheric  air  from  the  vessel  in  which  the  generation  takes  place, 
before  the  hydrogen  is  ignited,  as  otherwise  an  explosion  may  result. 

Experiment  3.  Place  a  few  pieces  of  granulated  zinc  (about  10  grammes)  in 
a  flask  of  about  200  c.c.  capacity,  which  is  arranged  as  shown  in  Fig.  38.  Cover 
the  zinc  with  water,  and  pour  upon  it  through  the  funnel  tube  a  little  sulphuric 
acid,  adding  more  when  gas  ceases  to  be  evolved.  Notice  the  effervescence 
around  the  zinc.  Collect  the  gas  in  test-tubes  over  water  and  ignite  it  by  taking 
the  test-tube  (with  mouth  downward)  to  a  flame  near  by.  Notice  that  the  first 
portions  of  gas  collected,  which  are  a  mixture  of  hydrogen  and  atmospheric 
air,  explode  when  ignited  in  the  test-tube,  while  the  subsequent  portions  burn 
quietly.  Pour  the  contents  of  one  test-tube  into  another  one  by  allowing  the 
light  hydrogen  gas  to  rise  into  and  replace  the  air  in  a  test-tube  held  over  the 
one  filled  with  hydrogen.  Take  two  test-tubes  completely  filled  with  the  gas; 
hold  one  mouth  upward,  the  other  one  mouth  downward :  notice  that  from  the 
first  one  the  gas  escapes  after  a  few  seconds,  while  it  remains  in  the  second 
tube  a  few  minutes,  as  may  be  shown  by  holding  the  tubes  near  a  flame  to 
cause  ignition. 
10 


146 


NON-METALS  AND  THEIR  COMBINATIONS. 


After  having  ascertained  that  all  atmospheric  air  has  been  expelled  from  the 
flask,  the  gas  may  be  ignited  directly  at  the  mouth  of  the  delivery  tube,  after 
moving  it  out  of  the  water. 

Continue  to  add  acid  until  the  zinc  is  nearly  all  dissolved,  remembering  that 
the  action  is  not  instantaneous  and  some  time  should  be  allowed  before  the 
next  addition  of  acid.  Warming  the  flask  will  hasten  the  action,  and  as  long 
as  small  gas-bubbles  arise  from  the  zinc,  action  is  not  over.  Avoid  adding  too 
much  acid,  but  if  there  is  an  excess,  it  may  be  removed  by  adding  more  zinc. 
Note  the  dark  particles  floating  in  the  liquid  and  the  bad  odor  of  the  hydrogen, 
which  are  due  to  the  impurities  in  the  zinc.  Finally,  filter  the  solution  (by 
folding  a  circle  of  filter-paper  twice  at  right  angles  through  the  center,  open- 
ing it  into  a  cone,  placing  in  a  funnel,  wetting  with  water,  and  pouring  the 
solution  into  it),  and  evaporate  it  to  about  one-third  its  volume  at  a  tempera- 
ture a  little  below  boiling.  Set  aside  a  day  to  cool  and  crystallize.  If  no 
crystals  appear,  evaporate  further,  The  crystals  are  zinc  sulphate,  the  same 


FIG.  38. 


Apparatus  for  generating  hydrogen. 

as  is  used  in  medicine.  They  are  an  illustration  of  the  formation  of  a  salt  by 
the  action  of  an  add  on  a  metal.  Filter  the  crystals  and  examine  them  care- 
fully. Expose  some  to  the  air  for  several  days.  Does  any  change  take  place  ? 
Save  the  crystals  for  Experiment  37. 

Experiment  4.  Pour  into  a  test-tube  of  not  less  than  50  c.c.  capacity,  5  c.c.  of 
hydrochloric  acid,  fill  up  with  water,  close  the  tube  with  the  thumb  and  set  it 
inverted  into  a  porcelain  dish  partly  filled  with  water.  Weigh  of  metallic 
zinc  0.04  gramme,  and  bring  it  quickly  under  the  mouth  of  the  test-tube,  so 
that  the  generated  hydrogen  rises  in  the  tube.  Prepare  a  second  tube  in  the 
same  manner,  and  introduce  0.04  gramme  of  metallic  magnesium.  In  case  the 
decomposition  of  the  acids  by  the  metals  should  proceed  too  slowly,  a  little 
more  acid  may  be  poured  into  the  dishes. 

When  the  metals  are  completely  dissolved  it  will  be  seen  that  the  volumes 
of  hydrogen  in  the  two  tubes  bear  a  relation  to  each  other  of  about  10  to  27. 

In  order  to  measure  the  gas  volumes  as  correctly  as  the  simple  apparatus 
permits,  the  tubes  should  be  transferred  to  a  large  beaker  filled  with  cold  water, 


HYDROGEN.  147 

bringing  the  surfaces  of  the  liquids  in  the  test-tube  and  beaker  on  a  level,  and 
marking  on  the  outside  of  the  test-tubes  (with  a  file  or  paper  strip)  the  exact 
height  of  the  gas. 

After  having  emptied  the  test-tubes,  they  may  be  filled  with  water  from  a 
pipette  or  from  a  burette  to  the  point  which  has  been  marked,  and  thus  the 
exact  volume  of  gas  generated  is  ascertained. 

Kepeat  the  operation,  using  0.065  gramme  of  zinc  and  0.024  gramme  of  mag- 
nesium. Notice  that  in  this  case  equal  volumes  of  hydrogen  are  obtained. 
Calculate  the  weight  of  hydrogen  from  the  cubic  centimetres  liberated,  and 
compare  this  weight  with  the  weights  of  zinc  and  magnesium  used.  What 
relation  is  there  between  the  weights  of  the  liberated  hydrogen  and  the  metala 
used,  and  the  atomic  weights  of  these  three  elements  ? 

Properties.  Hydrogen  is  a  colorless,  inodorous,  tasteless  gas ;  it 
is  the  lightest  of  all  known  substances,  having  a  specific  gravity  of 
0.0695  as  compared  with  atmospheric  air  (  =  1).  One  liter  of  hydro- 
gen at  0°  C.  (32°  F.),  and  a  barometric  pressure  of  760  mm.,  weighs 
0.08987  gramme,  or  one  gramme  occupies  a  space  of  11.127  liters; 
100  cubic  inches  weigh  about  2.265  grains. 

Hydrogen  and  helium  resist  liquefaction  more  than  other  gases.  Hydro- 
gen has  been  liquefied  by  causing  the  gas,  cooled  to  a  temperature  of 
—  205°  C.  ( — 337°  F.),  to  escape  under  certain  conditions  from  a  vessel  in 
which  it  was  stored  at  a  pressure  of  180  atmospheres.  Liquid  hydrogen  is 
clear  and  colorless ;  it  has  a  sp.  gr.  of  0.07,  and  boils  at  —  253°  C.  (-  423°  F.), 
under  normal  atmospheric  pressure ;  it  also  has  been  solidified  lately,  and  the 
temperature  reached  is  thought  to  be  about  — 256°  C.  (—428°  F.). 

In  its  chemical  properties,  hydrogen  resembles  the  metals  more  than 
the  non-metals ;  it  burns  easily  in  atmospheric  air,  or  in  pure  oxygen, 
with  a  non-luminous,  colorless,  or  slightly  bluish  flame  producing 
during  this  process  of  combustion  a  higher  temperature  than  can  be 
obtained  by  the  combustion  of  an  equal  weight  of  any  other  substance. 

Two  volumes  of  hydrogen  combine  with  one  volume  of  oxygen, 
forming  two  volumes  of  gaseous  water,  and  the  formation  of  water 
by  the  combustion  of  hydrogen  distinguishes  it  from  other  gases. 

The  chemical  affinity  which  hydrogen  possesses  for  oxygen  is  so 
great  that  it  abstracts   the  oxygen  from  many  oxides.     Thus,  if 
hydrogen  at  a  red  heat  be  passed  over  the  oxides  of  copper  or  iron 
the  metals  are  set  free,  while  water  is  formed : 
CuO  +  2H  =  H20  +  Cu. 

This  process  of  abstracting  oxygen  from  an  oxide  is  called  reduc- 
tion or  deoxidation,  and  substances  having  the  power  of  accomplish- 
ing this  result  are  called  reducing  or  deoxidizing  agents.  Hydrogen, 
consequently,  is  a  reducing  agent.  . 


148  NON-METALS  AND   THEIR  COMBINATIONS. 

We  thus  see  that,  while  in  physical  properties  O  and  H  resemble 
one  another  closely,  their  chemical  properties  are  practically  the  re- 
verse of  each  other.  Elements  which,  like  the  metals,  combine  readily 
with  oxygen,  do  not  combine  with  hydrogen  ;  and,  vice  versa,  ele- 
ments which,  like  chlorine,  combine  most  readily  with  hydrogen,  will 
scarcely  combine  with  oxygen.  It  will  be  shown  later  that,  as  a 
general  rule,  elements  which  resemble  one  another  in  chemical  prop- 
erties are  not  apt  to  combine  with  one  another,  while  those  differing 
widely  have  great  affinity  for  one  another. 

Nascent  hydrogen.  It  was  stated  above  that  hydrogen  is  a  good  reduc- 
ing agent,  but  as  far  as  hydrogen  in  the  free  state  is  concerned  reduction  takes 
place,  as  a  rule,  only  when  heat  is  employed.  There  is  a  condition  of  hydrogen, 
however,  in  which  it  is  able  to  reduce  many  compounds  at  ordinary  tempera- 
ture, while  free  hydrogen  has  no  measurable  action  on  the  same.  For  exam- 
ple, the  hydrogen  liberated  during  electrolysis  of  a  dilute  acid  is  able  to  reduce 
many  compounds  present  in  solution  immediately  around  the  pole  (cathode)  at 
which  the  hydrogen  is  produced.  It  also  shows  different  degrees  of  activity 
according  to  the  material  of  which  the  pole  is  made.  Similarly,  hydrogen 
generated  by  the  action  of  dilute  acids  on  metals  has  reducing  power  on  sub- 
stances immediately  surrounding  the  metals  during  action,  whereas  free 
hydrogen  gas  passed  through  a  solution  of  the  same  substances  or  in  contact 
with  them  in  the  dry  state  has  no  action.  To  illustrate  :  hydrogen  gas  passed 
through  a  solution  of  arsenous  oxide,  As203,  has  no  effect,  but  if  the  oxide  is 
present  in  a  mixture  of  dilute  hydrochloric  acid  and  zinc  the  hydrogen  formed 
quickly  reduces  it  to  arsine  gas,  AsH3.  This  is  one  of  the  most  delicate  tests 
for  arsenic.  The  more  active  condition  of  hydrogen  at  the  time  of  its  libera- 
tion is  spoken  of  as  the  nascent  state.  It  seems  that  this  increased  activity  of 
hydrogen  in  contact  with  the  substances  that  liberate  it  is  an  example  of  con- 
tact or  catalytic  action  (see  page  154).  Good  support  to  this  view  is  the  fact 
that  the  efficiency  of  the  nascent  hydrogen  varies  according  to  the  nature  of 
the  material  in  association  with  which  the  hydrogen  is  produced. 

Water,  H2O  =  17.88.  Hydrogen  monoxide.  Water  exists  on 
our  globe  in  the  three  states  of  aggregation.  Air  at  all  temperatures 
contains  water  in  the  gaseous  form.  Liquid  water  occurs  plentifully 
in  the  oceans,  rivers,  etc.,  and  also  in  plants  and  animals.  Seven- 
tenths  of  the  human  body  is  water;  potatoes  contain  of  it  75  per 
cent,  and  watermelons  as  much  as  94  per  cent.  Solid  water  exists 
not  only  as  ice  and  snow,  but  it  also  enters  into  the  composition  of 
many  rocks,  and  is  a  constituent  of  many  crystals  containing  water 
of  crystallization. 

Absolutely  pure  water  is  not  found  in  nature.  The  purest  natural 
water  is  rain-water  collected  after  the  air  has  been  purified  from 
dust,  etc.,  by  previous  rain.  Comparatively  pure  water  may  be 


WATER.  149 

obtained  by  melting  ice,  since,  when  water  containing  impurities  is 
frozen  partially,  these  are  mostly  left  in  the  uncongeaieu  water. 

The  waters  of  springs,  wells,  rivers,  etc.,  differ  widely  from  each 
other ;  they  all  contain  more  or  less  of  substances  dissolved  by  the 
water  in  its  course  through  the  atmosphere  or  through  the  soil  and 
rocks.  The  constituents  thus  absorbed  by  the  water  are  either  solids 
or  gases. 

Solids  generally  found  in  natural  waters  are  common  salt  (sodium 
chloride),  gypsum  (calcium  sulphate),  and  carbonate  of  lime  (calcium 
carbonate)  ;  frequently  found  are  chlorides  and  sulphates  of  potassium 
and  magnesium,  traces  of  silica  and  salts  of  iron.  Gases  absorbed 
by  water  are  constituents  of  the  atmospheric  air,  chiefly  oxygen, 
nitrogen,  and  carbon  dioxide.  One  hundred  volumes  of  water  con- 
tain about  two  volumes  of  nitrogen,  one  volume  of  oxygen,  and  one 
volume  of  carbon  dioxide. 

Water  is  said  to  be  hard  when  it  contains  so  much  of  salts  of  cal- 
cium and  magnesium  that  the  formation  of  lather  by  soap  is  delayed 
because  these  salts  form  insoluble  compounds  with  the  soap.  Water 
containing  but  little  of  inorganic  matter  is  said  to  be  soft. 

When  the  hardness  is  caused  by  metallic  sulphates  or  chlorides  the 
water  is  called  permanently  hard,  while  it  is  termed  temporarily  hard 
when  the  metals  are  present  as  carbonates,  dissolved  by  carbonic  acid. 
On  boiling  such  water  carbon  dioxide  escapes,  the  carbonates  of  the 
metals  are  precipitated,  and  the  water  is  rendered  soft. 

Mineral  waters  are  spring  waters  containing  one  or  more  sub- 
stances in  such  quantities  that  they  impart  to  the  water  a  peculiar 
taste  and  generally  a  decided  medicinal  action.  According  to  the 
predominating  constituents  we  distinguish  bitter  waters,  containing 
larger  quantities  of  magnesium  salts ;  iron  or  chalybeate  waters, 
containing  carbonate  or  sulphate  of  iron ;  sulphur  or  hepatic  waters, 
containing  hydrogen  sulphide ;  effervescent  waters,  strongly  charged 
with  carbonic  acid ;  cathartic  waters,  generally  containing  sodium  or 
magnesium  sulphate,  etc. 

Drinking-water.  A  good  drinking-water  should  be  free  from 
color,  odor,  and  taste  ;  it  should  neither  be  an  absolutely  pure  water, 
nor  a  water  containing  too  much  of  foreign  matter.  Water  containing 
from  2  to  4  parts  of  total  inorganic  solids  (chiefly  carbonate  of  lime 
and  common  salt)  in  10,000  parts  of  water  and  about  1  volume  of 
carbon  dioxide  in  100  volumes  of  water,  may  be  said  to  be  a  good 


150  NON-METALS  AND  THEIR  COMBINATIONS. 

drinking-water.  There  are,  however,  good  drinking-waters  which 
contain  more  of  total  solids  than  the  amount  mentioned  above. 

Most  objectionable  in  drinking-water  are  organic  substances,  espe- 
cially when  derived  from  animal  matter,  and  more  especially  when 
in  a  state  of  decomposition,  because  such  decomposing  organic  matter 
is  frequently  accompanied  by  living  organisms  (germs)  which  may 
cause  disease.  Boiling  of  water  destroys  these  germs,  and  by  subse- 
quent filtering  of  the  boiled  water  through  sand,  charcoal,  spongy 
iron,  etc.,  an  otherwise  unwholesome  water  may  be  rendered  fit  for 
drinking. 

In  nature  water  is  rendered  free  from  organic  impurities  by  the 
oxidizing  power  of  atmospheric  oxygen,  which  is  taken  up  by  the 
water  and  is  readily  transferred  upon  organic  matter  present. 

It  should  be  remembered  that  no  filter  can  remain  efficient  for  any  length 
of  time,  as  the  impurities  of  the  water  are  retained  by  the  materials  used  as  a 
filter,  and  this  may  become,  therefore,  a  source  of  pollution  instead  of  a  puri- 
fier. By  heating  to  a  low  red  heat  the  materials  used  for  filtering,  these  are 
cleaned  and  may  be  used  again.  The  methods  applied  to  the  analysis  of 
drinking-water  will  be  mentioned  later.  (See  Index.) 

Distilled  water,  Aqua  destillata.  The  process  for  obtaining 
pure  water  is  distillation  in  a  suitable  apparatus.  From  1000  parts 
of  water  used  for  distillation,  the  first  100  parts  distilled  over  should 
not  be  used,  as  they  contain  the  gaseous  constituents.  The  solids 
contained  in  the  water  are  left  in  the  undistilled  portion,  which  should 
not  be  less  than  100  parts. 

Composition  of  water.  Until  the  discovery  of  oxygen,  water 
was  thought  to  be  a  simple  substance.  In  1781  Cavendish,  of  Eng- 
land, discovered  the  qualitative  composition  of  water  when  he 
obtained  it  by  causing  hydrogen  and  oxygen  to  unite.  Water  was 
thus  produced  synthetically. 

The  proportion  of  hydrogen  and  oxygen  in  water  has  been  determined 
accurately  by  weighing  the  oxygen  and  the  water  formed  by  union  with  hydro- 
gen, also  by  weighing  both  constituents  and  the  water  after  union.  The  results 
of  the  most  accurate  experiments  showed  that  water  contains  11.185  per  cent. 
of  hydrogen  and  88.815  per  cent,  of  oxygen,  or  2  parts  by  weight  of  hydrogen 
to  15.88  parts,  by  weight,  of  oxygen.  It  has  been  ascertained  that  the  mole- 
cule of  water  is  made  up  of  two  atoms  of  hydrogen  and  one  atom  of  oxygen, 
H2O.  Hence,  it  follows  that  the  atomic  weight  of  oxygen  is  15.88.  By  vol- 
ume, hydrogen  and  oxygen  unite  in  the  proportion  of  2  :  1  to  form  water. 


WATER.  151 

Analysis  and  synthesis.  These  terms  refer  to  two  methods  of 
research  in  chemistry,  accomplished  by  two  kinds  of  reaction,  ana- 
lytical and  synthetical. 

Analysis  is  that  mode  of  research  by  which  compound  substances 
are  broken  up  into  their  elements  or  into  simpler  forms  of  combina- 
tion, and  analytical  reactions  are  all  chemical  processes  by  which  the 
nature  of  an  element,  or  of  a  group  of  elements,  may  be  recognized. 

Synthesis  is  that  method  of  research  by  which  bodies  are  made  to 
unite  to  produce  substances  more  complex. 

Analytical  and  synthetical  methods,  or  reactions,  frequently  blend 
into  one  another.  This  means :  A  reaction  made  with  the  intention 
of  recognizing  a  substance,  may  at  the  same  time  produce  some  com- 
pound of  interest  from  a  synthetical  point  of  view. 

Properties  of  water.  Water  is  an  inodorous,  tasteless,  and,  in 
small  quantities,  colorless  liquid.  Thick  layers  of  water  show  a  blue 
color.  On  cooling,  water  contracts  until  it  reaches  the  temperature 
of  4°  C.  (39.2°  F.),  at  which  point  it  has  its  greatest  density.  If 
cooled  below  this  temperature  it  expands  and  the  specific  gravity  of 
ice  is  somewhat  less  than  that  of  water.  Water  is  perfectly  neutral, 
yet  it  has  a  tendency  to  combine  with  both  acid  and  basic  substances. 
These  compounds  are  usually  called  hydroxides  (formerly  hydrates), 
such  as  NaOH,  Ca(OH)2,  etc.  These  compounds  are  often  formed  by 
direct  union  of  an  oxide  with  water,  thus  : 

CaO  +  H20  =  Ca(OH)2. 
SO3  +  H2O  =  SO2(OH)2. 

Water  is  the  most  common  solvent,  both  in  nature  and  in  artificial 
processes.  As  a  general  rule,  solids  are  dissolved  more  quickly  and 
in  larger  quantities  by  hot  water  than  by  cold,  but  to  this  there  are 
many  exceptions.  For  instance  :  Common  salt  is  nearly  as  soluble 
in  cold  as  in  hot  water ;  sodium  sulphate  is  most  soluble  in  water  of 
33°  C.  (91°  F.),  and  some  calcium  salts  are  less  soluble  in  hot  than 
in  cold  water. 

The  term  solution  is  applied  to  any  clear  and  homogeneous  liquid 
obtained  by  causing  the  transformation  of  matter  from  a  solid  or 
gaseous  state  to  the  liquid  state  by  means  of  a  liquid  called  a  solvent 
or  menstruum ;  solutions  may  also  be  obtained  from  two  liquids,  as 
when  we  dissolve  oil  in  ether.  A  solution  is  said  to  be  saturated  when 
the  solvent  will  not  take  up  any  more  of  the  substance  being  dissolved. 

Two  kinds  of  solutions  are  distinguished — viz.,  simple  solutions  and  complex 
or  chemical  solutions.  In  the  former  we  have  a  mere  physical  change,  the  mole- 


152          ,        NON-METALS  AND   THEIR   COMBINATIONS. 

cules  of  the  dissolved  body  being  present  with  all  their  characteristic  proper- 
ties, and  on  evaporation  the  dissolved  solid  will  be  re-obtained  unchanged. 
Instances  of  this  kind  are  solutions  of  sugar  or  table  salt  and  water.  (The 
breaking  down  of  molecules  into  ions  during  simple  solution  will  be  considered 
later.) 

In  chemical  solutions  there  takes  place  a  rearrangement  of  the  atoms  within 
the  molecules,  both  of  the  solvent  and  of  the  substance  dissolved.  Moreover, 
on  evaporation  of  the  solution  a  substance  is  obtained  entirely  different  from 
the  one  which  has  been  dissolved.  Instances  of  this  kind  are  the  dissolving  of 
sodium  in  water,  when  sodium  hydroxide  is  formed ;  or  the  dissolving  of  zinc 
in  sulphuric  acid,  when  zinc  sulphate  is  formed.  The  term  emulsion  is  used 
to  designate  a  more  or  less  homogeneous  liquid  rendered  opaque  or  rnilky  by 
the  suspension  in  it  of  finely  divided  particles  of  fat,  oil,  or  resin.  The  milk 
of  mammalia  and  the  milk-like  juice  of  certain  plants  are  instances  of  true 
emulsions. 

Many  salts  combine  with  water  in  crystallizing ;  crystallized  sodium 
sulphate,  for  instance,  contains  more  than  half  its  weight  of  water. 
This  water  is  called  ivater  of  crystallization,  and  is  expelled  generally 
at  a  temperature  of  100°  C.  (212°F.).  Some  crystallized  substances 
lose  water  of  crystallization  when  exposed  to  the  air ;  this  property  is 
known  as  efflorescence.  Crystals  of  sodium  carbonate,  ferrous  sulphate, 
etc.,  effloresce,  as  is  shown  by  the  formation  of  powder  upon  the  crys- 
talline surface.  Substances  are  said  to  be  anhydrous  when  they  are 
destitute  of  water,  for  instance,  when  crystals  have  lost  their  water 
of  crystallization  or  when  ether  or  alcohol  have  been  freed  from  dis- 
solved water.  The  term  anhydride  is  sometimes  used  for  oxyacids 
which  have  been  deprived  of  all  water,  so  that  they  are  no  longer 
acids,  but  oxides.  Thus,  by  removing  water  from  sulphuric  acid, 
H2SO4,  there  is  left  sulphur  trioxide,  or  sulphuric  acid  anhydride, 
SO3.  The  term  deliquescence  is  applied  to  the  power  of  certain  solid 
substances  to  absorb  moisture  from  the  air,  thereby  becoming  damp 
or  even  liquid,  as,  for  instance,  potassium  hydroxide,  calcium  chloride, 
etc.  Such  substances  are  spoken  of  also  as  being  hygroscopic,  and 
are  used  for  drying  gases. 

The  term  effervescence  refers  to  the  escape  of  a  gas  from  water  or 
from  any  other  liquid  in  which  the  gas  was  held  under  pressure  or  in 
which  it  may  be  generated ;  as,  for  instance,  when  an  acid  is  added 
to  a  carbonate,  whereupon  carbon  dioxide  escapes  with  energetic 
bubbling. 

The  explanation  of  effervescence  and  deliquescence  is  found  in  a  well-known 
principle  of  physics.  It  is  well  known  that  liquids  will  evaporate  in  a  closed 
space  until  the  pressure  of  the  vapor  is  equal  to  the  vapor  tension  of  the  liquid, 


HYDROGEN  DIOXIDE.  153 

when  equilibrium  is  established  and  evaporation  of  the  liquid  apparently 
ceases.  This  means  that  vapor  particles  fly  back  into  the  liquid  at  the  same 
rate  that  liquid  particles  leave  the  surface  of  the  liquid  to  become  vapor.  If 
the  vapor  pressure  in  any  way  becomes  greater  than  the  vapor  tension  of  the 
liquid,  some  vapor  will  be  condensed  to  liquid.  On  the  other  hand,  if  the 
vapor  pressure  is  constantly  lower  than  the  vapor  tension  of  the  liquid,  evapo- 
ration will  go  on  until  no  more  liquid  is  left.  One  way  of  accomplishing  this 
is  by  free  exposure  of  liquids  to  the  atmosphere.  Of  course  the  amount  of  the 
vapor  pressure  varies  with  the  temperature.  Now  it  is  found  that  substances 
containing  water  of  crystallization  have  a  vapor  tension  just  as  water  has. 
For  example,  when  a  crystal  of  sodium  sulphate  (Na2SO4.10H20)  is  allowed 
to  rise  to  the  top  of  a  barometer  tube  at  9°  C.,  it  exerts  a  vapor  tension  of  5.5 
mm. — that  is,  the  pressure  of  the  water  vapor  given  off  by  the  crystal  is  enough 
to  depress  the  mercury  column  5.5  mm.  Those  substances  crystallizing  with 
water  which  at  ordinary  temperature  exert  a  vapor  tension  greater  than  the 
pressure  of  the  water  vapor  in  the  atmosphere,  are  efflorescent  and  must  be 
kept  in  closed  containers,  just  as  water  must  be  to  prevent  loss  of  water. 
When  the  vapor  tension  of  the  substances  is  about  the  same  or  less  than  the 
atmospheric  vapor  pressure,  the  substances  are  stable  and  need  not  be  carefully 
bottled,  except  to  keep  them  clean.  The  average  pressure  of  the  water  vapor 
in  the  atmosphere  at  9°  C.  is  about  5  mm.  At  this  temperature  crystals  of 
sodium  sulphate  have  a  vapor  tension  of  5.5  mm.  and  are  efflorescent,  while 
those  of  copper  sulphate  have  a  vapor  tension  of  2  mm.  and  are  stable  in  the 
air. 

Deliquescent  substances  are  always  very  soluble  in  water.  A  layer  of 
moisture  condenses  on  these  just  as  it  does  on  all  bodies  exposed  to  the  atmo- 
sphere. In  the  case  of  extremely  soluble  substances,  the  condensed  moisture 
forms  a  thin  layer  of  very  concentrated  solution  upon  their  surfaces.  Concen- 
trated solutions  have  a  vapor  tension  less  than  that  of  water,  and  much  less 
than  the  atmospheric  vapor  pressure.  The  result  is  that  water  vapor  continues 
to  condense  from  the  atmosphere  upon  the  substances  until  they  dissolve  and 
form  solutions  so  dilute  that  their  correspondingly  increased  vapor  tension  bal- 
ances the  vapor  pressure  of  the  moisture  in  the  atmosphere. 

0-H 
Hydrogen  dioxide,  Hydrogen  peroxide,  H2O2,  or   I       •      This 

O — H 

compound  may  be  obtained  in  aqueous  solution  from  several  metallic 
dioxides  which,  when  treated  with  an  acid,  yield  a  portion  of  their 
oxygen  to  water. 

Sodium  dioxide  and  barium  dioxide  are  the  compounds  chiefly 
employed  in  its  manufacture,  the  acid  used  being  either  carbonic, 
hydrochloric,  hydrofluoric,  sulphuric,  or  phosphoric  acid.  The  de- 
composition, when  sulphuric  acid  and  barium  dioxide  are  used,  is 
this : 

BaO2  +  H2SO4  =  BaSO4  +  H2O2. 


154  NON-METALS  AND    THEIR   COMBINATIONS. 

In  no  case  is  it  possible  to  obtain,  as  might  appear  from  the 
above  equation,  pure  hydrogen  dioxide  directly,  as  a  considerable 
quantity  of  water  has  to  be  present  in  order  to  effect  the  de- 
composition. The  aqueous  solution,  if  quite  pure,  can  be  concen- 
trated by  evaporation  at  a  temperature  not  exceeding  60°  C.  (140° 
F.)  until  it  has  a  strength  of  50  per  cent.  If  this  be  further  heated 
in  vacuo  at  a  gradually  increased  temperature,  a  nearly  pure  hydro- 
gen dioxide  distils  over  at  a  temperature  of  85°  C.  (185°  F.). 

Pure  hydrogen  dioxide  is  a  colorless,  oily  liquid,  of  a  specific 
gravity  1.45.  It  is  soluble  in  water,  alcohol,  and  ether,  which  latter 
extracts  it  from  its  aqueous  solutions. 

Hydrogen  dioxide  decomposes  slowly  at  ordinary  temperature, 
more  rapidly  on  exposure  to  light  and  at  higher  temperatures ;  at 
100°  C.  the  decomposition  is  often  explosively  rapid.  Many  inert 
subtances,  in  powder,  cause  its  decomposition,  and  it  is  for  this 
reason  that  even  dust  particles  from  the  air  act  decomposingly, 
especially  during  evaporation.  The  presence  of  very  small  quanti- 
ties of  certain  substances  retards  the  decomposition.  Traces  of  free 
acids,  as  also  boro-glycerin,  have  been  used  for  this  purpose.  It  has 
been  found  that  a  very  small  quantity  of  acetanilide  is  an  excellent 
preservative  and  it  is  now  added  to  commercial  hydrogen  dioxide 
solution. 

Catalytic  action.  There  are  a  number  of  instances  in  chemistry 
where  a  substance,  which  apparently  undergoes  no  change  itself, 
causes  by  its  presence  an  increase  in  chemical  change  in  other  sub- 
stances, or  induces  a  change  where,  without  it,  there  would  be  no 
chemical  action.  This  is  known  as  catalytic  or  contact  action  and 
the  process  is  called  catalysis.  Examples  of  this  action  are  seen  in 
the  decomposition  of  hydrogen  dioxide  by  dust  particles,  or  finely 
divided  platinum,  the  influence  of  manganese  dioxide  on  potassium 
chlorate  in  the  preparation  of  oxygen,  and  the  explosion  of  a  mixture 
of  hydrogen  and  oxygen  when  platinum  black  is  introduced  into  it. 

Hydrogen  dioxide  possesses  bleaching,  caustic,  and  antiseptic 
properties.  It  is  used  as  a  bleaching  agent  for  hair,  wool,  teeth,  and 
other  articles,  and  as  an  antiseptic  in  surgical  and  in  dental  opera- 
tions. It  effervesces  with  pus,  as  also  with  saliva,  in  consequence  of 
the  liberation  of  oxygen. 

Solution  of  hydrogen  dioxide,  Aqua  hydrogenii  dioxidi,  should 
contain  about  3  per  cent,  by  weight,  of  pure  dioxide,  corresponding 
to  about  10  volumes  of  available  oxygen  in  1  volume  of  the  solution. 


HYDROGEN  DIOXIDE.  155 

The  solution  is  colorless  and  without  odor,  and  has  a  slightly  acidu- 
lous taste,  producing  a  peculiar  sensation  and  soapy  froth  in  the 
mouth.  It  is  liable  to  deteriorate  by  age,  especially  on  exposure  to 
heat  and  light. 

Pyrozone  is  the  trade  name  under  which  a  50  per  cent,  hydrogen  peroxide 
is  sold,  but  diluted  pyrozone  also  is  found  in  the  market. 

Glycozone  is  hydrogen  dioxide  dissolved  in  glycerin  instead  of  in  water. 

Hydrogen  dioxide,  owing  to  its  instability  and  tendency  to  decom- 
pose into  water  and  oxygen,  is  an  excellent  oxidizing  agent.  It  is 
frequently  used  in  preference  to  other  such  agen-ts,  because  by  its  use 
no  other  products  are  introduced  into  solutions  than  water  and  oxy- 
gen. Toward  a  few  substances,  which  themselves  are  unstable  and 
easily  give  up  oxygen,  it  also  acts  as  a  reducing  agent.  For  example, 
silver  oxide  is  reduced  to  metallic  silver  thus : 

Ag20  +  H202  =  2Ag  -f  02  +  H20. 

When  hydrogen  dioxide  decomposes  into  water  and  oxygen,  heat  is  liberated. 
The  thermal  equation  is — 

H2O2  =  H2O  +  O  -f  22,926  cal. 

that  is,  when  33.76  grammes  of  hydrogen  dioxide  corresponding  to  the  formula, 
H202,  decomposes,  22,926  calories  of  heat  energy  are  liberated.  This  is  in 
addition  to  the  heat  that  is  produced  when  the  liberated  oxygen  unites  with 
other  substances.  In  this  way  the  great  activity  of  hydrogen  dioxide  as  an 
oxidizer  is  accounted  for. 

Tests 1  for  solution  of  hydrogen  dioxide. 

(Use  the  commercial  solution  after  diluting  about  five  times  with  water.) 

1.  To  a  beaker  half  full  of  water,   add   1  or  2  c.c.  of  solution  of 

potassium  iodide   (see   Reagents)  and   about  2  c.c.  of  the  hydrogen 

dioxide  solution.     Is  any  yellow  color  produced  ?     Then  add  a  few 

drops  of  starch  solution  (for  which,  see  Index).     A  deep  blue  color 

is  produced  by  the  action  of  the  starch  on  the  iodine  liberated  from 

potassium  iodide  by  the  oxidizing  action  of  the  hydrogen  dioxide : 

2KI  -f  H202  =  2KOH  +  21. 
The  action  is  more  intense  if  the  water  is  first  acidified  with  5  or  10 

1  Tests  are  reactions  to  which  a  substance  may  be  subjected  for  the  purpose  of  recognition. 
Acids  turn  blue  litmus  red,  and  we  call  that  a  test  for  acids.  Carbon  dioxide  gas  gives  a 
milky  appearance  to  lime-water,  which  is  a  test  for  the  gas.  Some  tests  are  much  more  strik- 
ing than  others,  indeed,  they  are  so  characteristic  that  they  tell  at  once  the  nature  of  the  sub- 
stance tested.  Such  tests  might  be  called  decisive,  in  distinction  to  others  which  are  only  cor- 
roborative, and  to  which  several  substances  may  respond. 


156  NON-METALS  AND  THEIR  COMBINATIONS. 

drops  of  a  dilute  acid.     This  is  not  a  decisive  test,  since  other  sub- 
stances besides  hydrogen  dioxide  give  the  same  test. 

2.  To  a  test-tube  half  full  of  water,  add  in  succession,  1  c.c.  of  the 
hydrogen  dioxide  solution,  a  few  drops  of  dilute  sulphuric  acid,  and 
2  drops  of  solution  of  potassium  dichromate,  and  mix.     A  blue  com- 
pound, known  as  perchromic  acid,  HCrO4,  is  produced,  which  fades 
after  a  short  time.       The  color  may  be   made  more  permanent  by 
shaking  the  mixture  with  ether,   which   dissolves   the  compound  and 
collects  on  the  surface  on   standing.      This  is  a  very  delicate  and 
decisive  test. 

3.  Acidify  a  few  c.c.  of  the  hydrogen  dioxide  solution  with  about 
2  c.c.   of  dilute  sulphuric  acid,  and  add   solution  of  potassium  per- 
manganate, a  little  at  a  time.   The  purple  color  vanishes  quickly  and 
a  gas  is  given  off  (oxygen).      The   permanganate  is  an  unstable  oxi- 
dizing agent,  which  gives  up  its  oxygen.     This  unites  with  oxygen 
from  the  dioxide,  and  escapes  as  a  gas.     The  reaction  will  be  under- 
stood when  the  chemistry  of  manganese  is  studied.    Other  substances 
also  decolorize  permanganate. 

If  a  solution  is  colorless,  odorless,  practically  neutral  to  litmus- 
paper,  volatilizes  completely  upon  heating,  and  responds  to  the  above 
tests,  especially  number  2,  it  is,  without  doubt,  hydrogen  dioxide. 

QUESTIONS. — Mention  two  processes  by  which  hydrogen  may  be  obtained. 
Show  by  symbols  the  decomposition  of  water  by  potassium,  and  of  sulphuric 
acid  by  iron.  State  the  chemical  and  physical  properties  of  hydrogen.  Define 
the  nascent  state.  What  explanation  is  offered  to  account  for  it?  State  the 
composition  of  water  in  parts  by  weight  and  by  volume.  Mention  the  most 
common  solid  and  gaseous  constituents  of  natural  waters.  How  does  a  mineral 
water  differ  from  other  waters?  Mention  some  different  kinds  of  mineral 
waters  and  their  chief  constituents.  What  are  the  characteristics  of  a  good 
drinking-water  ?  What  are  the  purest  natural  waters,  and  by  what  process 
may  chemically  pure  water  be  obtained?  State  composition,  mode  of  manu- 
facture, and  properties  of  hydrogen  dioxide.  What  is  the  explanation  of  efflo- 
rescence and  deliquescence  ? 


SOLUTION.  157 

12.  SOLUTION. 

As  stated  under  Water,  the  term  solution  is  applied  to  any  homo- 
geneous liquid  mixture  that  results  when  solids,  liquids,  or  gases 
an;  brought  in  contact  with  a  liquid  and  disappear  in  the  liquid. 
(There  are  a  few  instances  of  solution  of  a  gas  in  a  solid,  and  of  a 
solid  in  a  solid.)  Solutions  are  transparent,  and  the  dissolved  mate- 
rial is  so  thoroughly  disseminated  that  its  particles  cannot  be  dis- 
tinguished by  the  eye  from  those  of  the  solvent.  Moreover,  there  is 
perfect  distribution  of  the  dissolved  matter  and  no  tendency  for  it  to 
settle.  An  opalescent  or  opaque  appearance  of  a  liquid  is  evidence 
that  there  is  matter  held  in  suspension,  and  this  matter  will  settle  in 
time,  or  may  be  filtered  out.  Dissolved  substances  cannot  be  re- 
moved by  filtration,  as  they  pass  through  the  pores  of  the  paper  as 
readily  as  the  liquid  does. 

For  the  majority  of  substances  there  is  a  limit  to  the  amount  that 
can  be  dissolved  in  a  given  amount  of  liquid.  This  limit  ranges 
from  an  almost  infinitesimal  amount  in  some  cases  to  a  fairly  large 
quantity  in  others.  Thus,  at  ordinary  temperature,  the  amount  of 
ferric  oxide  that  is  dissolved  by  100  c.c.  of  pure  water  is  extremely 
small,  while  about  90  grammes  of  crystallized  magnesium  sulphate  are 
dissolved.  No  substance  is  absolutely  insoluble,  but  many  are  so 
sparingly  soluble  that  for  practical  purposes  they  are  considered  in- 
soluble. In  some  cases  two  substances  may  be  mixed  in  any  pro- 
portions, for  example,  water  and  alcohol.  But  usually  the  solubility 
of  one  liquid  in  another  is  limited,  and  when  two  such  liquids  are 
shaken  together  they  separate  after  a  time  into  two  layers,  the  liquid 
in  each  layer  being  saturated  with  the  other  liquid.  Thus,  when  ether 
and  water  are  shaken  together  at  ordinary  temperature  they  separate 
on  standing  with  the  lighter  (ether)  layer  on  top,  and  100  grammes 
of  water  dissolve  2.1  grammes  of  ether,  while  100  grammes  of  ether 
dissolve  11  grammes  of  water.  Pairs  of  liquids  which  are  only  slightly 
soluble  in  each  other  are  known  as  immiscible  solvents,  and  are  often 
employed  in  certain  kinds  of  chemical  work  for  transferring  a  sub- 
stance from  one  liquid  to  another.  This  operation  is  known  as  ex- 
traction, and  depends  for  its  success  upon  a  great  difference  of  solu- 
bility of  the  given  substance  in  the  two  solvents.  The  division  of  a 
substance  between  two  immiscible  solvents,  after  thorough  shaking 
and  separation  of  the  liquids,  is  proportional  to  its  solubility  in  each 
solvent.  If  a  substance  is  100  times  more  soluble  in  chloroform 
than  in  water,  and  its  aqueous  solution  is  shaken  thoroughly  with 
chloroform,  the  concentration  of  the  substance  in  the  chloroform 


158  NON-METALS  AND   THEIR   COMBINATIONS. 

layer  will  be  found  100  times  that  in  the  water  layer.  The  process 
of  extraction  must  be  repeated  several  times  for  the  complete  removal 
of  a  substance  from  a  liquid. 

Terms  employed.  The  liquid  in  which  a  substance  is  dissolved 
is  called  the  solvent,  while  the  substance,  to  avoid  circumlocution,  is 
often  called  the  solute.  The  word  strength  is  frequently  used  to  refer 
to  the  amount  of  substance  in  solution,  but  a  more  exact  term  to 
employ  is  concentration.  A  solution  that  contains  a  small  quantity, 
say  5  grammes  of  a  substance  in  100  c.c.,  is  said  to  have  a  small  con- 
centration, or  to  be  dilute.  Concentrated  solutions  contain  a  relatively 
large  amount  of  dissolved  substance ;  they  are  often  spoken  of  as  very 
strong  solutions.  Concentrating  a  solution  is  the  removal  of  part  of 
the  solvent  by  evaporation.  A  saturated  solution  is  one  that  contains 
the  maximum  amount  of  dissolved  substance.  This  condition  may 
be  attained  by  long  agitation  of  the  liquid  with  an  excess  of  the  sub- 
stance. If  the  latter  is  a  solid,  it  should  be  finely  divided.  The 
solubility  of  a  substance  is  its  concentration  in  saturated  solution,  and 
is  expressed  in  terms  of  the  number  of  grammes  of  the  substance  in  100 
grammes  of  the  solvent,  or  in  100  c.c.  of  the  solution,  or  of  the  grammes 
of  solvent  required  to  dissolve  1  gramme  of  the  substance.  The  solu- 
bility of  substances  varies  with  the  temperature,  being,  as  a  rule,  in 
the  case  of  solids,  much  greater  at  boiling  than  at  ordinary  temper- 
ature. In  most  cases,  when  a  hot  concentrated  solution  is  allowed 
to  cool,  the  excess  of  material  over  what  corresponds  to  the  solubility 
at  lower  temperature,  separates  as  crystals  from  the  solution  (see 
Crystals,  Chapter  1).  But  in  some  instances  the  excess  of  material 
does  not  separate  from  the  solution  as  it  cools ;  such  a  solution  is 
then  said  to  be  supersaturated.  Crystallization  can  be  induced  by 
placing  in  the  cool  solution  a  fragment  of  the  same  substance  as  that 
in  solution.  A  solution  in  contact  with  the  solid  substance  cannot 
be  more  than  saturated  with  respect  to  that  substance.  There  is  an 
equilibrium  between  the  solid  and  the  saturated  solution.  Sulphate, 
thiosulphate,  and  chlorate  of  sodium  have  a  marked  tendency  to  give 
supersaturated  solutions,  especially  if  the  solutions  are  freed  from  all 
floating  particles  by  careful  filtration. 

The  solution  of  certain  substances  in  water  takes  place  with  libera- 
tion of  heat  and  rise  in  temperature  of  the  solution,  while  in  other 
cases  there  is  an  absorption  of  heat  and  a  fall  in  temperature.  Heat 
of  solution  is  the  number  of  calories  liberated  or  absorbed  when  the 
weight  of  a  substance  in  grammes  corresponding  to  its  chemical  form- 
ula (molecular  weight)  is  dissolved  in  an  unlimited  amount  of  water. 


SOLUTION.  159 

AVhen  95.35  grammes  of  sulphuric  acid  (corresponding  to  H2SOj  are 
thus  dissolved,  38,880  calories  of  heat  are  liberated,  or  enough  heat 
to  raise  over  38  liters  of  water  1°  C.  in  temperature.  When  284.11 
grammes  of  crystallized  sodium  carbonate  (Na2CO3.10H2O)  are  dis- 
solved, 16,038  calories  are  absorbed,  but  solution  of  an  equivalent 
weight  of  anhydrous  sodium  carbonate  (Na2CO3),  or  105.31  grammes, 
liberates  5,598  calories  of  heat.  If  a  substance  absorbs  heat  during 
solution,  it  develops  the  same  amount  of  heat  when  it  comes  out  of 
solution  as  by  crystallization.  For  example,  a  supersaturated  solu- 
tion of  sodium  sulphate,  when  crystallizing  suddenly,  produces  quite 
an  appreciable  rise  in  temperature. 

Solution  of  gases.  Henry's  Law.  Gases  dissolve  in  liquids  to  a  vari- 
able degree.  The  range  of  solubility  is  quite  wide,  as  may  be  seen  from  the 
following  examples:  At  0°  C.  and  760  mm.  pressure,  1  volume  of  water  dissolves 
0.02  volume  of  hydrogen,  or  nitrogen,  0.04  volume  of  oxygen,  1.8  volumes  of 
carbon  dioxide,  80  volumes  of  sulphur  dioxide,  550  volumes  of  hydrochloric 
acid  gas,  and  1050  volumes  of  ammonia  gas. 

The  solubility  of  a  gas  varies  with  the  nature  of  the  solvent;  thus,  at  0°  C., 
a  volume  of  alcohol  dissolves  twice  as  much  carbon  dioxide  as  the  same  volume 
of  water  does.  It  also  varies  with  the  temperature,  decreasing,  as  a  rule,  as  the 
temperature  increases.  Thus,  100  volumes  of  water  dissolve  about  4  volumes 
of  oxygen  at  0°  C.,  3  at  20°  C.,  1.8  at  50°  C.,  and  none  at  100°  C.  In  many 
instances  a  gas  is  completely  removed  from  its  solution  by  boiling,  but  this  is 
not  possible  in  the  case  of  certain  very  soluble  gases,  like  hydrochloric  acid. 
There  is  in  such  cases  a  chemical  action,  in  part  at  least,  between  the  gas  and 
the  solvent.  A  20.2  per  cent,  aqueous  solution  of  hydrochloric  acid  distills 
unchanged  under  normal  atmospheric  pressure. 

The  solubility  of  a  gas  increases  with  increased  pressure  on  the  gas.  Com- 
mercial aerated  water  is  a  good  illustration.  The  water  is  charged  with  carbon 
dioxide  under  considerable  pressure.  When  drawn  from  the  container  and 
exposed  to  the  atmosphere  the  excess  of  gas,  which  cannot  remain  dissolved 
under  the  diminished  pressure,  escapes,  causing  effervescence.  Such  a  solution 
is  often  called  soda  water.  Solutions  of  gases  in  liquids  fall  into  two  classes : 
(1)  those  from  which  the  gas  is  completely  removed  by  heat  or  by  decrease  of 
pressure ;  (2)  those  from  which  the  gas  is  not  thus  completely  removed.  Very 
soluble  gases  give  rise  to  the  second  class  of  solutions,  in  which  a  complete 
chemical  and  physical  independence  of  the  molecules  of  solvent  and  gas  is 
lacking.  In  solutions  of  the  first  class  there  is  a  fixed  relationship  between  the 
solubility  of  a  gas  and  pressure,  which  is  known  as  Henry's  Law.  It  may  be 
stated  thus :  The  quantity  of  a  gas  dissolved  by  a  given  quantify  of  a  liquid  is  pro- 
portional to  the  pressure  of  the  gas.  Since  the  volume  of  a  gas  is  inversely 
proportional  to  the  pressure,  another  form  in  which  the  law  may  be  stated  is : 
A  given  quantity  of  a  liquid  dissolves  the  same  volume  of  a  gas  at  all  pressures. 

In  the  case  of  a  mixture  of  gases  in  contact  with  a  liquid,  each  gas  dissolves 
as  if  it  were  present  alone,  and  in  proportion  to  its  own  partial  pressure  in  the 
mixture, 


160  NON-METALS  AND   THEIR   COMBINATIONS. 

Henry's  law  holds  in  the  case  of  absorption  of  gases  by  saline  solutions,  if 
the  gas  has  no  chemical  action  on  the  salt  in  solution,  for  example,  in  the 
absorption  of  carbon  dioxide,  oxygen,  or  nitrogen,  by  a  solution  of  sodium 
chloride  (common  salt).  When  the  gas  acts  chemically  on  the  dissolved  salt, 
as  carbon  dioxide  does  on  ordinary  sodium  phosphate  or  sodium  carbonate, 
one  portion  of  the  gas  is  absorbed  in  accordance  with  Henry's  law,  and  an 
additional  portion  is  absorbed  as  a  result  of  chemical  action  and  is  independent 
of  pressure. 

Freezing-points  of  solutions.  The  freezing-point  of  a  solution  is  always 
lower  than  that  of  the  pure  solvent.  It  is  also  easily  observed,  by  introducing 
small  quantities  of  solutions  and  pure  solvents  over  the  mercury  in  barometer 
tubes,  that  the  vapor  tension  of  the  solutions  is  always  less  than  that  of  the 
pure  solvents,  no  matter  what  the  temperature  is.  This  difference  in  vapor 
tension  accounts  for  the  fact  that  the  freezing-point  of  solutions  is  depressed. 
Theoretical  considerations  show  that  freezing  (separation  of  some  of  the  solvent 
in  the  solid  state)  can  take  place  only  at  such  a  temperature  at  which  the  solu- 
tion and  the  solid  state  of  the  solvent  have  the  same  vapor  tension,  whereby 
they  are  in  physical  equilibrium  and  can  co-exist  permanently  (see  discussion 
under  Efflorescence  and  Deliquescence,  p.  152).  Since  the  vapor  tension  of  a 
solution  is  always  less  than  that  of  the  pure  solvent,  it  follows  that  the  freezing- 
point  of  a  solution  must  be  lower  than  that  of  the  pure  solvent,  in  order  that 
the  vapor  tension  of  the  solution  and  of  the  ice  that  separates  may  balance 
each  other.  (On  this  principle  the  low  temperature  of  freezing  mixtures,  such 
as  snow  (or  ice)  and  salt,  is  explained). 

For  a  description  of  apparatus  and  details  of  method  in  making  determina- 
tions of  the  freezing-points  of  solutions,  the  student  must  be  referred  to  books 
on  physical  chemistry. 

For  solutions  not  too  concentrated  and  in  which  there  is  no  chemical  action 
between  the  solvent  and  the  substance  dissolved,  the  following  law  has  been 
found  to  hold  :  The  depression  of  the  freezing-point  is  directly  proportional  to  the 
iveight  of  dissolved  substance  in  a  given  amount  of  the  solvent.  By  calculations 
made  on  the  results  obtained  with  dilute  solutions,  the  following  law  has  been 
found  to  hold  theoretically  for  molecular  quantities  of  substances  :  The  molec- 
ular weights  in  grammes  of  different  substances  dissolved  in  1000  grammes  of  the 
same  solvent  produce  the  same  depression  of  the  freeezing -point.  The  depression 
thus  produced  is  called  the  molecular  depression  constant,  and  has  a  different 
numerical  value  for  each  solvent.  For  water  it  is  1.89°  C.;  for  benzene,  4.9°  C., 
and  for  phenol,  7.5°  C. 

The  above  law  gives  a  basis  for  a  method  of  determining  molecular  weights, 
which  was  first  applied  extensively  by  Raoult,  and  is  sometimes  called  the 
cryoscopic  method.  It  is  valuable  in  the  case  of  substances  which  cannot  be 
volatilized  without  decomposition.  The  molecular  weight  is  calculated  from 
the  equation 

D  =  d  X  Vv-' 

M  X  g 

in  which  D  is  the  amount  of  depression  in  any  actual  experiment,  d  the  molec- 
ular depression  constant,  W  the  weight  of  the  substance,  M  its  molecular 
weight,  and  g  the  weight  of  the  solvent  in  grammes. 


SOLUTION.  161 

The  above  law,  often  called  the  law  of  Eaoult,  does  not  hold  in  some  cases, 
especially  in  those  of  solutions  of  acids,  bases,  and  salts  in  water.  For  ex- 
ample, one  molecular  weight  of  sodium  chloride,  58.06  grammes,  dissolved  in 
1000  grammes  of  water,  depresses  the  freezing-point  about  3.5°  C.,  or  nearly 
twice  the  amount  produced  by  a  cane-sugar  solution  of  equivalent  concentra- 
tion, 1.89°  C.,  which  is  taken  as  the  molecular  depression  of  normally  acting 
substances.  It  is  also  a  noteworthy  fact  that  aqueous  solutions  of  substances 
that  have  abnormal  freezing-point  depressions  are  just  such  as  conduct  an 
electric  current,  while  solutions  of  substances  that  give  normal  depressions  do 
not  conduct  a  current.  The  same  number  of  molecules  of  different  substances 
in  a  given  amount  of  solvent  produces  the  same  lowering  of  the  freezing-point, 
and  the  molecular  weights  in  grammes  contain  the  same  number  of  molecules. 
The  fact  that  the  depression  of  the  freezing-point  of  a  solution  of  the  molecular 
weight  in  grammes  of  sodium  chloride  in  1000  grammes  of  water  is  much 
greater  than  that  of  a  similar  solution  of  cane-sugar,  can  be  accounted  for  on 
the  assumption  that  the  number  of  particles  in  the  sodium  chloride  solution 
must  be  increased  somehow  over  the  number  of  particles  in  the  sugar  solution. 
This  increase  can  only  take  place  by  a  decomposition  of  the  molecule  of  sodium 
chloride,  thus, 

NaCl  •=  Na  +  Cl. 

The  particles  Na  and  Cl  must  be  different  in  condition  from  sodium  and  chlo- 
rine as  we  know  them  in  the  free  state,  but  as  far  as  their  effect  upon  the 
freezing-point  is  concerned  they  act  the  same  as  undecomposed  dissolved  mole- 
cules. This  assumption  of  the  decomposition  of  molecules  is  applied  in  the 
case  of  all  abnormally  acting  solutions  where  the  freezing-point  depressions 
are  greater  than  normal,  and  will  be  referred  to  again  farther  on  under 
lonization. 

In  the  field  of  medicine  the  determination  of  the  freezing-point  of  certain 
fluids  is  sometimes  carried  out  in  order  to  learn  something  of  the  manner  in 
which  the  organs  are  functioning.  Normal  blood  has  a  lower  freezing-point 
than  water,  the  difference  is  0.56°  C.  A  greater  difference  than  this  indicates 
that  the  kidneys  are  not  properly  eliminating  the  solid  waste  products  from 
the  blood.  The  freezing-point  depression  of  normal  urine  is  1.2°-2.3°  C.  Of 
cows'  milk  it  is  0.55°-0.56°  C.  A  lower  depression  indicates  that  the  milk  has 
been  tampered  with. 

Boiling-points  of  solutions.  These  are  always  higher  than  the  boiling- 
points  of  the  pure  solvents.  The  boiling-point  of  any  solution  is  that  temper- 
ature at  which  the  vapor  tension  of  the  solution  is  equal  to  the  atmospheric 
pressure.  Since  the  vapor  tension  of  solutions  is  less  than  that  of  the  pure 
solvent,  it  follows  that  a  solution  must  be  heated  to  a  higher  temperature  than 
that  at  which  the  pure  solvent  boils,  in  order  to  make  its  vapor  tension  equal 
to  the  atmospheric  pressure ;  in  other  words,  to  make  it  boil.  The  elevations  in 
the  boiling-points  are  proportional  to  the  concentrations  of  the  different  solutions  of 
any  one  substance.  The  molecular  weight  in  grammes  of  normally  acting  sub- 
stances, dissolved  in  1000  grammes  of  water,  elevates  the  boiling-point  from 
100°  to  100.52°  C.  The  difference,  0.52°,  is  called  the  molecular  boiling-point 
constant  for  water.  Just  as  in  the  case  of  freezing-points,  so  here  a  method 
11 


162  NON-METALS  AND   THEIR   COMBINATIONS. 

of  determining  molecular  weights  has  been  devised,  but  for  a  description 
of  the  apparatus  and  details  of  working,  reference  must  be  made  to  special 
books. 

The  substances  which  show  abnormalities  in  the  depression  of  the  freezing- 
point  are  also  those  which  give  abnormal  elevations  in  the  boiling-points  of 
their  solutions.  The  abnormal  behavior  is  also  accounted  for  by  the  same  ex- 
planation, namely,  a  decomposition  of  some  of  the  molecules  of  the  dissolved 
substance.  The  deviations  from  normal  behavior  are  particularly  observed  in 
aqueous  solutions. 

Osmotic  pressure.  Soluble  substances  in  contact  with  a  liquid  dissolve 
and  diffuse  throughout  the  liquid  until  the  concentration  is  uniform  in  every 
part  of  the  solution  (see  Diffusion,  p.  40).  In  the  liquid  the  substance  behaves 
somewhat  like  a  gas,  in  that  its  molecules  tend  to  spread  out  and  fill  the  whole 
space  occupied  by  the  liquid.  The  cohesion  between  the  molecules  of  the  sub- 
stance is  overcome  and  there  is  freedom  of  motion,  somewhat  as  in  a  gas. 
Just  as  a  gas  exerts  a  pressure  on  any  partition  or  membrane  that  resists  the 
motion  of  its  molecules,  so  likewise  do  the  molecules  of  a  substance  in  solution 
exert  pressure  upon  a  membrane  that  prevents  their  diffusion  into  a  less  con- 
centrated region  of  the  solution,  or  into  the  pure  solvent.  This  pressure  is 
called  osmotic  pressure.  In  the  article  on  Dialysis  it  is  shown  that  a  substance 
in  aqueous  solution  on  one  side  of  certain  kinds  of  membranes,  as  bladder  or 
parchment,  will  diffuse  into  pure  water  on  the  other  side.  Osmotic  pressure  is 
exhibited  here,  but  such  membranes  are  not  suitable  for  its  study,  because  the 
motion  (diffusion)  of  the  molecules  of  the  dissolved  substance  is  not  stopped, 
but  only  hindered.  It  is  possible,  however,  to  prepare  membranes  which  are 
permeable  to  the  solvent,  but  impermeable  to  the  dissolved  substance.  These 
are  known  as  semi-permeable  membranes,  and  by  their  means  the  phenomena 
of  osmotic  pressure  can  be  studied  qualitatively  and  quantitatively.  W. 
Pfeffer,  a  botanist,  was  the  first  to  successfully  construct  (1877)  an  artificial 
semi-permeable  membrane  by  causing  a  precipitate  of  copper  ferrocyanide  to 
be  formed  within  the  walls  of  a  porous  unglazed  porcelain  cup.1  Such  cups 
are  known  as  osmotic  cells.  When  a  solution  of  any  substance,  say,  cane-sugar, 
is  placed  in  the  cell  and  the  latter  is  placed  in  water,  it  is  observed  that  water 
passes  through  the  cell  into  the  solution,  but  no  sugar  passes  out  into  the 
water.  If  the  flow  of  water  is  unobstructed,  it  will  continue  until  the  solution 
is  so  much  diluted  that  it  is  practically  the  same  as  water.  If  the  accumulation 
of  water  in  the  cell  is  obstructed  by  using  a  closed  cell  filled  with  the  solution 
and  fitted  with  a  manometer,  pressure  is  seen  to  develop  in  the  cell,  due  to  the 
tendency  of  the  water  to  pass  into  it,  and  corresponding  to  the  amount  that 
would  have  passed  into  it  had  the  water  not  been  obstructed.  It  requires  some 
hours  for  this  pressure  to  reach  a  maximum,  and  the  amount  in  atmospheres 
can  be  read  on  the  manometer.  At  the  maximum  the  pressure  on  the  water 
within  the  cell  causes  it  to  tend  to  flow  out  as  fast  as  the  water  outside  tends 
to  flow  in,  thus  producing  a  system  in  equilibrium.  The  pressure  read  on  the 
manometer  is  equal  to  the  osmotic  pressure  of  the  molecules  of  the  dissolved 
substance  against  the  membrane  of  the  cell. 

1  It  was  rather  difficult  to  prepare  such  membranes  until  a  method  was  devised  by  Prof. 
H.  N.  Morse,  by  which  practically  flawless  osmotic  cups  can  be  readily  made.  See  Amer- 
Chem.  Jour.,  July,  1905,  and  later. 


SOLUTION.  163 

In  osmotic  cells  the  pure  solvent  always  passes  into  the  solution,  or  the  sol- 
vent passes  from  a  solution  of  less  concentration  into  one  of  greater  concentra- 
tion. This  flow  can  be  accounted  for  on  the  physical  principle  of  equilibrium, 
namely,  that  in  any  system  capable  of  movement  or  adjustment  a  strain  in  one 
part  will  cause  a  movement  tending  to  remove  or  equalize  the  strain.  A 
system  of  a  membrane  and  a  liquid  on  each  side  of  it  can  be  in  equilibrium 
only  when  the  osmotic  pressure  on  the  two  sides  of  the  membrane  is  the  same. 
In  the  case  of  a  semi-permeable  membrane,  the  molecules  of  the  dissolved  sub- 
stance cannot  pass,  so  the  only  other  way  of  equalizing  osmotic  pressure  is  by 
the  solvent  passing  from  the  exterior  of  the  cell  into  the  solution,  until  the 
osmotic  pressure  is  the  same  on  each  side  of  the  membrane.  If  this  passage  is 
obstructed  the  tendency  still  exists,  which  manifests  itself  as  pressure. 

In  1887  van't  Hoff  deduced  from  theoretical  considerations  the  laws  of 
osmotic  pressure,  which  are  verified  by  experiments.  These  laws  are  analogous 
to  the  gas  laws,  and  are  as  follows  : 

The  osmotic  pressures  of  solutions  of  the  same  substance  are  proportional  to  their 
concentrations.  This  is  analogous  to  Boyle's  law  for  gas  pressures,  and  in  gen- 
eral is  independent  of  the  nature  of  the  solvent.  It  is  illustrated  by  the 
following  results : 


Grammes  of  cane-sugar  in  1000  grammes  of  water..  .    . 

68.4 

136.8 

171 

342 

483 

972 

1215 

2446 

Osmotic  pressure  increases  in  proportion  to  the  absolute  temperature.  This  is 
analogous  to  the  law  of  Charles  for  gases. 

Solutions  which  at  the  same  temperature  have  equal  osmotic  pressure  contain 
equal  numbers  of  molecules  of  the  dissolved  substance  in  equal  volumes.  This  is 
analogous  to  Avogadro's  law  for  gases. 

The  osmotic  pressure  of  a  substance  in  solution  is  the  same  in  value  as  the  gas- 
eous pressure  which  it  would  exhibit  if  the  same  weight  of  it  were  contained  as  a 
gas  in  the  same  volume  at  the  same  temperature.  The  osmotic  pressure  of  a  solution 
of  the  molecular  weight  in  grammes  of  a  substance  in  one  liter  of  water  at  0° 
G.  is  22  to  23  atmospheres,  and  the  same  weight  of  the  substance  in  gas  form 
at  0°  C.,  and  occupying  a  liter  volume,  would  have  a  gas  pressure  of  22  to  23 
atmospheres. 

Solutions  of  different  substances  having  the  same  osmotic  pressure  are  said 
to  be  is-osmotic  or  isofonic.  It  is  not  an  easy  matter  to  carry  out  measurements 
of  osmotic  pressure  except  in  specially  equipped  laboratories,  but  isotonic 
solutions  can  be  prepared,  nevertheless,  by  taking  advantage  of  the  fact  that 
such  solutions  have  the  same  freezing-points,  and  determination  of  freezing- 
points  is  a  routine  task  in  laboratories.  Blood-serum  freezes  at — 0.56°  C., 
which  corresponds  to  an  osmotic  pressure  of  about  6.6  atmospheres.  A  0.95 
per  cent,  aqueous  solution  of  sodium  chloride  freezes  at  — 0.56°  C.,  and,  there- 
fore, exerts  the  same  osmotic  pressure  as  blood-serum.  It  is  isotonic  with 
blood-serum.  A  solution  of  higher  osmotic  pressure  than  that  of  blood-serum 
is  called  hypertonic,  and  one  of  lower  pressure  is  called  hypotonic. 


164  NON-METALS  AND   THEIR   COMBINATIONS. 

In  regard  to  the  laws  of  osmotic  pressure,  deviations  from  them  are  observed 
in  the  case  of  aqueous  solutions  of  the  same  substances  for  which  the  freezing- 
point  and  boiling-point  laws  do  not  hold,  namely,  acids,  bases,  and  salts. 
These  always  show  greater  osmotic  pressures  than  those  calculated,  and  than 
that  shown  by  cane-sugar,  which  is  a  type  of  normally  acting  substance.  The 
deviations  are  explained  by  the  same  assumption  that  is  made  to  explain  devi- 
ations from  the  freezing-point  law  (see  above),  namely,  decomposition  of  mole- 
cules into  a  greater  number  of  particles,  that  is,  ions. 


13.  NITROGEN. 
Niii  =  14  (13.93). 

Occurrence  in  nature.  By  far  the  larger  quantity  of  nitrogen  is 
found  in  the  atmosphere  in  a  free  state.  Compounds  containing 
nitrogen  are  chiefly  the  nitrates,  ammonia,  and  many  organic  sub- 
stances. 

Preparation.  Nitrogen  is  obtained  usually  from  atmospheric  air 
by  the  removal  of  its  oxygen.  This  may  be  accomplished  by  burn- 
ing a  piece  of  phosphorus  in  a  confined  portion  of  air,  when  phos- 
phoric oxide,  a  white  solid  substance,  is  formed,  while  nitrogen  is  left 
in  an  almost  pure  state. 

Other  methods  for  obtaining  nitrogen  are  by  heating  a  mixture  of 
potassium  nitrite  and  ammonium  chloride  dissolved  in  water : 

KNO2  -f  NH4C1  =  KC1  -f  2H2O  +  2N; 
or  by  heating  ammonium  nitrite  in  a  glass  retort : 
NH4NO2  =  2H20  +  2N. 

Experiment  5.  Use  an  apparatus  as  shown  in  Fig.  37,  page  140.  Place  in  the 
flask  about  10  grammes  of  potassium  nitrite  and  nearly  the  same  amount  of 
ammonium  chloride;  add  enough  water  to  dissolve  the  salts,  and  apply  heat, 
which  is  to  be  carefully  regulated  from  the  time  the  decomposition  begins,  as 


QUESTIONS. — Give  a  definition  of  solution  and  its  general  characteristics. 
What  are  immiscible  solvents  and  how  are  they  employed?  Define  dilute, 
concentrated,  and  saturated  solutions.  What  is  meant  by  the  solubility  of  a 
substance,  and  by  heat  of  solution  ?  What  is  Henry's  law  regarding  the  solu- 
tion of  gases  in  liquids?  What  is  the  relation  between  the  freezing-points  of 
solutions  and  the  weights  of  dissolved  substances?  What  use  is  made  of  the 
cryoscopic  method  ?  What  is  osmotic  pressure?  What  is  a  semi-permeable 
membrane?  How  do  the  laws  of  osmotic  pressure  compare  with  the  gas  laws? 
What  are  isotonic,  hypertonic,  and  hypotonic  solutions  ?  What  is  the  expla- 
nation of  the  abnormal  behavior  shown  by  solutions  of  acids,  bases,  and  salts 
in  their  freezing-points,  boiling-points,  and  osmotic  pressures? 


NITROGEN.  165 

the  evolution  of  gas  may  otherwise  become  too  rapid.     Collect  the  gas,  and 
notice  its  properties  mentioned  below. 

Properties.  Nitrogen  is  a  colorless,  inodorous,  tasteless  gas; 
which,  at  a  temperature  of —130°  C.  (—202°  F.)  and  a  pressure  of 
280  atmospheres,  may  be  condensed  to  a  colorless  liquid.  It  is  neither, 
like  oxygen,  a  supporter  of  combustion,  nor,  like  hydrogen,  a  com- 
bustible substance ;  in  fact,  nitrogen  is  distinguished  by  having  very 
little  affinity  for  any  other  element,  and  it  scarcely  enters  directly  into 
combination  with  any  substance.  Nitrogen  is  not  poisonous,  yet  not 
being  a  supporter  of  combustion  it  cannot  sustain  animal  life. 
Nitrogen  is  trivalent  in  some  compounds,  quinquivalent  in  others. 

Atmospheric  air  is  a  mixture  of  about  four-fifths  of  nitrogen  and 
one-fifth  of  oxygen,  with  small  quantities  of  aqueous  vapor,  argon, 
carbon  dioxide,  and  ammonia,  containing  frequently  also  traces  of 
nitrous  or  nitric  acid,  and  occasionally  hydrogen  sulphide,  sulphur 
dioxide,  and  hydrocarbons.  Besides  these  gases  there  are  always 
suspended  in  the  air  solid  particles  of  dust  and  very  minute  cells  of 
either  animal  or  vegetable  origin. 

100  volumes  of  atmospheric  air  contain  of 

Oxygen 20.60  volumes. 

Nitrogen 77.16       " 

Argon 0.80  volume. 

Carbon  dioxide        .        .        .        .      0.03-0.04       " 
Aqueous  vapor         ....      0.5  -1.40       " 

Ammonia     }  .    traces. 

Nitric  acid    -* 

Omitting  all  minor  constituents,  the  composition  of  air  by  volume 
is  about  79  per  cent,  of  nitrogen  and  21  per  cent,  of  oxygen,  corre- 
sponding in  weight  to  77  per  cent,  of  nitrogen  and  23  per  cent,  of 
oxygen. 

That  atmospheric  air  is  a  mixture  and  not  a  compound  of  oxygen  and 
nitrogen  is  shown  by  the  facts  that  the  composition  is  not  absolutely  constant, 
that  the  two  elements  may  be  mixed  in  the  proper  quantities  without  showing 
the  least  evidence  that  chemical  change  has  taken  place,  and  that  pure  water 
absorbs  from  air  the  two  elements  in  quantities  different  from  those  in  which 
they  occur  in  air. 

Humidity,  specifically  called  relative  humidity,  designates  the  amount 
of  aqueous  vapor  in  the  atmosphere,  compared  with  that  which  is 
required  to  saturate  it  at  the  respective  temperature.  When  the  air 
is  completely  saturated  the  humidity  is  expressed  at  100;  if  perfectly 


166  NON-METALS  AND   THEIR   COMBINATIONS. 

dry,  as  0.     The  instruments  used  to  determine  humidity  are  called 
hygrometers. 

An  analysis  of  air  maybe  made  by  the  following  method  :  A  graduated  glass 
tube,  containing  a  measured  volume  of  air,  is  placed  with  the  open  end  down- 
ward into  a  dish  containing  mercury.  A  small  piece  of  phosphorus  is  then 
introduced  and  allowed  to  remain  in  contact  with  the  air  for  several  hours, 
when  it  gradually  combines  with  the  oxygen.  The  remaining  volume  of  air  is 
chiefly  nitrogen,  the  loss  in  volume  represents  oxygen. 

For  the  determination  of  carbon  dioxide  and  water,  a  measured  volume  of 
.air  is  passed  through  two  U-shaped  glass  tubes.  One  of  these  tubes  has  previ- 
ously been  filled  with  pieces  of  calcium  chloride,  the  other  tube  with  pieces  of 
potassium  hydroxide,  and  both  tubes  have  been  weighed  separately.  In  pass- 
ing the  measured  air  through  these  tubes  the  first  one  will  retain  all  the 
moisture,  the  second  one  all  the  carbon  dioxide ;  the  increase  in  weight  of  the 
tubes  at  the  end  of  the  operation  will  give  the  amounts  of  the  two  constituents. 

That  oxygen  is  found  in  the  atmosphere  in  a  free  state  is  explained 
by  the  fact  that  all  elements  having  affinity  for  oxygen  have  entered 
into  combination  with  it,  while  the  excess  is  left  uncombined.  Mtro- 
gen  is  found  uncombined,  because  it  has  so  little  affinity  for  other 
elements. 

Liquefaction  of  air  on  a  large  scale  has  been  made  possible  by  a  process 
which  depends  on  first  subjecting  air  to  a  pressure  of  2000  pounds  to  the  square 
inch  and  then  permitting  the  compressed  gases  to  escape  from  a  needle-point 
orifice.  During  the  expansion  of  the  gas  heat  is  absorbed,  i.  e.,  the  air  as  well 
as  the  tubes  in  which  it  is  contained  are  cooled  off'.  The  cold  thus  produced 
is  used  to  cool  another  portion  of  compressed  air,  which,  on  expanding,  becomes 
colder  than  the  first  portion.  By  repeating  the  operation  a  third  time  the 
temperature  is  brought  down  to  — 191°  C.  and  below,  and  at  this  temperature 
liquefaction  takes  place. 

Liquefied  air  is  a  mobile,  slightly  bluish  liquid  which  can  be  kept  for  some 
little  time  in  open  vessels— i.  e.,  so  long  as  the  temperature  of  nearly  200°  C. 
below  freezing  is  maintained  by  the  evaporation  of  the  liquid. 

As  nitrogen  is  somewhat  more  volatile  than  oxygen,  the  liquefied  air,  when 
permitted  to  stand  in  open  vessels,  becomes  gradually  richer  in  oxygen,  so  that 
finally  a  liquid  is  left  containing  over  80  per  cent,  of  oxygen.  Notwithstand- 
ing the  low  temperature  of  this  liquid  it  acts  most  energetically  as  a  supporter 
of  combustion. 

Of  interest  are  the  changes  which  are  brought  about  in  the  physical  proper- 
ties of  different  bodies  when  cooled  down  to  nearly  — 200°  by  immersion  in 
liquid  air.  Many  malleable  metals,  many  soft  or  elastic  bodies,  such  as  rubber 
and  paraffin,  when  subjected  to  this  low  temperature,  become  as  brittle  as  badly 
cooled  glass ;  changes  in  color,  as  well  as  in  other  properties,  take  place  also. 

Argon,  mentioned  above  as  a  normal  constituent  of  air,  is  a  gaseous  element, 
discovered  in  1894.  It  may  appear  strange  that  a  normal  constituent  of  air, 
present  to  the  extent  of  nearly  1  per  cent.,  should  have  been  overlooked  for  so 
many  years,  although  air  had  been  carefully  analyzed  many  hundred  times. 


NITROGEN.  167 

The  only  explanation  that  can  be  offered  is  the  fact  that  argon  has  scarcely 
any  chemical  affinity  for  other  elements,  and  consequently  its  presence  was  not 
revealed  by  any  of  the  ordinary  reactions  used  in  air  analysis.  In  fact,  the 
total  of  argon  present  had  invariably  been  reported  as  nitrogen  up  to  the  time 
of  the  discovery  of  the  new  element. 

Helium  is  another  gaseous  element  discovered  in  1895.  It  occurs  absorbed 
in  a  number  of  rare  minerals  from  which  it  is  expelled  by  heating.  It  is  also 
a  constituent  of  the  gases  which  are  disengaged  from  certain  spring  waters, 
and,  in  very  small  quantities,  is  a  constituent  of  atmospheric  air.  Both  argon 
and  helium  are  very  inert.  Helium  has  an  atomic  weight  of  about  4,  while 
that  of  argon  is  40.  One  volume  of  helium  is  contained  in  245,000  volumes  of 
air. 

Compounds  of  nitrogen.  Nitrogen  has  very  little  tendency  to 
combine  directly  with  other  elements,  bat  it  is  an  easy  matter  to 
obtain  compounds  of  nitrogen.  These,  however,  are  all  obtained  in 
indirect  ways,  being  either  furnished  ready  made  by  processes  of  nature 
or  obtained  as  by-products  in  manufacturing  industries.  Conversely, 
as  a  result  of  the  inactivity  of  nitrogen,  most  of  its  compounds  are 
more  or  less  unstable,  either  at  ordinary  or  elevated  temperatures,  or 
when  brought  together  with  other  substances.  We  have  already  seen 
how  easily  ammonium  nitrite  is  radically  decomposed  by  heat,  and 
ammonium  nitrate  acts  in  the  same  way,  as  will  be  seen  below. 

The  two  principal  compounds  of  nitrogen  are  ammonia  and  nitric 
acid,  and  nearly  all  the  others  with  which  we  have  to  do  in  inorganic 
chemistry  are  derived  from  these.  The  valence  of  nitrogen  is  3  in 
ammonia,  which  represents  the  limit  of  reduction,  while  it  is  5  in 
nitric  acid,  which  is  the  limit  of  oxidation  of  nitrogen. 

Ammonia,  NH3  — 16.93.  This  compound  is  constantly  forming 
in  nature  by  the  decomposition  of  organic  (chiefly  animal)  matter,  such 
as  meat,  urine,  blood,  etc.  It  is  also  obtained  during  the  process  of 
destructive  distillation,  which  is  the  heating  of  non-volatile  organic 
substances  in  suitable  vessels  to  such  an  extent  that  decomposition 
takes  place,  the  generated  volatile  products  being  collected  in  re- 
ceivers. The  manufacture  of  illuminating  gas  is  such  a  process  of 
destructive  distillation ;  coal  is  heated  in  retorts,  and  most  of  the 
nitrogen  contained  in  the  coal  is  converted  into  and  liberated  as 
ammonia  gas,  which  is  absorbed  in  water,  through  which  the  gas  is 
made  to  pass.  This  is  the  source  of  nearly  all  the  ammonium  salts 
on  the  market. 

Another  method  of  obtaining  ammonia  is  through  decomposition 
of  ammonium  salts  by  the  hydroxides  of  sodium,  potassium,  or  cal- 


168 


NON-METALS  AND   THEIR   COMBINATIONS. 


cium.     Usually  ammonium  chloride  is  mixed  with  calcium  hydroxide 

and  heated,  when  calcium  chloride,  water,  and  ammonia  are  formed : 

2(NH4C1)  +  Ca(OH)2  =  CaCl2  +  2H2O  +  21sTH3. 

Experiment  6.  Mix  about  equal  weights  (10  grammes  of  each)  of  ammonium 
chloride  and  calcium  hydroxide  (slaked  lime)  in  a  flask  of  about  200  c.c.  capac- 
ity, and  arranged  as  in  Fig.  39;  cover  the  mixture  with  water  and  apply  heat. 


FIG.  39. 


Apparatus  for  generating  amuioiiia. 

As  long  as  any  atmospheric  air  remains  in  the  apparatus,  bubbles  of  it  will 
pass  through  the  water  contained  in  the  cylinder;  afterward  all  gas  will  be 
readily  and  completely  absorbed  by  the  water.  Notice  the  odor  and  alkaline 
reaction  on  litmus  of  the  ammonia  water  thus  obtained.  When  the  gas  is 
being  freely  liberated,  move  the  tube  upward,  as  shown  in  B,  and  collect  the 
gas  by  upward  displacement  in  a  cylinder  or  tube,  which  when  filled  with  gas 
is  held  mouth  downward  into  water,  which  will  rapidly  rise  in  the  tube  by 
absorption  of  the  gas.  Notice  that  ammonia  is  not  readily  combustible,  by 
applying  a  flame  to  the  gas  escaping  from  the  delivery  tube. 

Ammonia  is  a  colorless  gas,  of  a  very  pungent  odor,  an  alkaline 
taste,  and  a  strong  alkaline  reaction.  In  pure  oxygen  it  burns,  form- 
ing water  and  free  nitrogen. 

By  the  mere  application  of  a  pressure  of  seven  atmospheres  or  by 
intense  cold  (—40°  C.,  —40°  F.),  ammonia  may  be  converted  into  a 
liquid,  which  at  —80°  C.  (—112°  F.)  forms  a  solid  crystalline  mass. 
Water,  at  its  freezing-point,  dissolves  as  much  as  1050  volumes  of 
ammonia  gas,  and  at  15°  C.  (59°  F.)  still  retains  727  volumes  of  the 
gas  in  solution.  This  solution  contains  ammonium  hydroxide  : 
NH3  +  H20  =  NH4OH. 

Certain  experimental  evidence  indicates  that  only  a  small  propor- 
tion of  the  gas  is  combined  with  water  to  form  hydroxide,  most  of  it 


NITROGEN.  169 

being  simply  dissolved.  By  boiling,  all  the  ammonia  is  finally  driven 
out  of  solution. 

It  has  a  strong  alkaline  action  on  litmus  and  has  basic  properties 
like  those  of  sodium  and  potassium  hydroxide.  It  neutralizes  acids 
forming  salts,  thus : 

NH4OH  +  HC1  =  NH4C1  +  H2O. 

Ammonia  gas  also  unites  with  acids  directly  without  elimination  of 
water.  For  example,  with  hydrochloric  acid  gas,  a  dense  white  cloud 
of  ammonium  chloride  is  formed  : 

NH3  +  HC1  •=  NH4C1. 

The  union  of  water  or  hydrochloric  acid  directly  with  ammonia  is 
explained  by  the  increase  of  valence  of  the  nitrogen  atom  from  3  to 
5.  In  the  hydroxide  and  all  the  salts,  there  is  a  group  of  atoms, 
(NH4)— ,  which  acts  exactly  like  an  atom  of  metal.  It  has,  therefore, 
been  called  ammonium.  This  radical  and  its  analytical  reactions  will 
be  discussed  under  Ammonium  compounds. 

Experiment  7.  To  about  20  c.c.  of  dilute  ammonia  water,  add  concentrated 
hydrochloric  acid  until  litmus-paper  is  just  turned  from  blue  to  red  by  the 
liquid.  Evaporate  to  dryness  in  a  porcelain  dish  over  a  small  flame.  Note 
appearance  of  residue  and  compare  its  taste  with  that  of  the  ammonia  water, 
and  dilute  hydrochloric  acid  and  also  that  of  ammonium  chloride.  What  is 
the  residue?  This  is  an  example  of  the  formation  of  a  salt  by  neutralization 
of  an  acid  by  an  alkali. 

Ammonia  "water,  Aqua  ammoniae  (Spirit  of  hartshorn).  This  is 
a  solution  of  ammonia  gas  in  water  or  ammonium  hydroxide  in  water. 
The  common  ammonia  water  contains  10  per  cent,  by  weight,  equal 
to  125  volumes  of  ammonia,  and  has  a  specific  gravity  of  0.958  at 
25°  C. ;  the  stronger  ammonia  water,  aqua  ammonias  fortior,  contains 
28  per  cent.,  and  has  a  specific  gravity  of  0.897  at  25°  C.  Ammonia 
water  has  the  odor,  taste,  and  reaction  which  characterize  the  gas. 

Hydrazine,  N2H4  (Diamine],  is  a  compound  obtainable  from  organic  com- 
pounds by  processes  which  cannot  be  considered  here.  It  is  a  colorless  gas  at 
summer  heat,  readily  liquefying  at  a  somewhat  lower  temperature,  and  solidi- 
fying at  the  freezing-point  of  water. 

Exposed  to  the  air  it  takes  up  oxygen,  forming  water  and  nitrogen.  In  its 
chemical  properties  hydrazine  resembles  ammonia,  forming  a  hydrate  of 
the  composition  N2H4.H2O,  and  salts  with  acids,  such  as  N2H4.H2SO4  and 
N2H4(HC1)2.  The  constitution  of  hydrazine  may  be  represented  by  the 

H\  /H 

formula        >N — NC 

H/          \H 

Hydroxylamine,  NH2OH.    The  term   amine  is  used  to  designate  com- 


170  NON-METALS  AND   THEIR   COMBINATIONS. 

pounds  derived  from  ammonia  by  replacement  of  one  or  more  hydrogen  atoms 
by  basic  atoms  or  radicals,  and  it  is  in  keeping  with  this  terminology  that  the 
compound  under  consideration  is  known  as  hydroxyl-amine,  while  hydrazine 
is  termed  di-amine. 

Hydroxylamine  is  prepared  by  the  action  of  nascent  hydrogen  on  nitric  acid : 

HN03  +   6H   =  NH2OH    -f   2H2O. 

The  compound  is  known  only  in  solution  ;  with  acids  it  forms  well-defined 
salts,  which  appear  to  be  ammonium  salts  in  which  a  hydrogen  atom  has  been 
replaced  by  hydroxyl.  The  formation  of  salts  may  be  represented  thus : 

NH2OH   +HN03-  NH3OHNOS 
NH2OH   +   HC1  ==  NH3OHC1 

Triazoic  acid,  N3H  (Hydrazoic  add).  This  remarkable  substance  was  first 
isolated  in  1890  from  organic  compounds.  It  is  now  obtained  also  from  inor- 
ganic material  by  the  action  of  sodium  on  ammonia,  when  a  compound  of 
the  composition  NH2Na  is  formed,  which  by  treatment  with  nitrogen  monoxide 
produces  water  and  sodium  triazoate.  The  latter,  by  the  action  of  an  acid,  is 
converted  into  a  sodium  salt  and  free  triazoic  acid.  The  three  steps  of  the 
process  may  be  represented  thus : 

NH3  +  Na  =  NH2Na  +  H 

NH2Na  +  N20  =  Na  —  N/  ||  +  H2O 

/N  /N 

2Na-N/  ||  +  H2SO4  =  Na2SO4  +  2HN/  |^ 


Triazoic  acid  is  a  colorless  gas,  possessing  a  disagreeable  odor.  It  is  soluble 
in  water,  and  this  solution  can  be  distilled,  but  the  operation  is  dangerous,  as 
the  compound  is  apt  to  decompose  with  explosive  violence.  When  inhaled  it 
acts  as  a  poison,  producing  violent  headache. 

While  the  three  compounds  of  hydrogen  with  nitrogen  considered  above  are 
of  a  basic  nature,  triazoic  acid  has  decidedly  acid  properties.  In  fact,  it  is  a 
stronger  acid  than  acetic  acid,  and  resembles  hydrochloric  acid  in  precipitating 
soluble  silver  and  rnercurous  salts. 

Compounds  of  nitrogen  and  oxygen.  Five  distinct  compounds 
of  nitrogen  and  oxygen  are  known.  They  are  named  and  constituted 
as  follows : 

Composition. 

By  weight.  By  volume. 

NO  NO 

Nitrogen  monoxide,  N2O       ...  28  16  2  1 

Nitric  oxide,  NO 28  32  2  2 

Nitrogen  trioxide,  N2O3         ...  28  48  2  3 

Nitrogen  tetroxide,  N2O4  =  2(NO2)       .  28  64  24 

Nitrogen  pentoxide,  N2O5      ...  28  80  2  5 

The  trioxide  and  pentoxide  are  called  also  acid  anhydrides,  or  ni- 
trous and  nitric  anhydride  respectively,  because  they  combine  with 


NITROGEN.  171 

water  to  give  nitrous  and  nitric  acid.  Conversely,  when  the  acids  are 
deprived  of  the  elements  of  water,  the  respective  oxides  of  nitrogen 
are  obtained.  The  monoxide  corresponds  to  hyponitrous  acid, 
H2N2O2,  but  does  not  yield  the  acid  with  water.  It  is,  hence,  not  an 
anhydride.  All  of  the  oxides  are  obtained  from  nitric  acid,  directly 
or  indirectly.  The  last  one  is  formed  by  abstraction  of  water  from 
nitric  acid,  the  others  involve  reduction  of  nitric  acid  or,  in  reality, 
of  nitrogen  pentoxide. 

While  our  knowledge  of  the  structure  of  the  oxides  of  nitrogen  is  unsatis- 
factory, the  following  graphic  formulas,  in  which  the  valence  of  nitrogen  is 
assumed  to  be  either  1,  3,  or  5,  have  been  proposed  to  show  the  manner  in  which 
the  atoms  may  be  linked  together : 

Nitrogen  monoxide,  N—  O  —  N  or  N  —  N 

Nitric  oxide,  N  =  O 

Nitrogen  trioxide,  O  =  N  —  O  —  N=Oor 


Nitrogen  tetroxide, 


Nitrogen  pentoxide, 


Nitrogen  tetroxide,  at  high  temperature,  has  the  composition  N02,  and  it  is 
possible  that  in  NO2,  and  nitric  oxide,  NO,  the  valence  of  nitrogen  is  4  and  2 
respectively.  The  truth  is  that  we  have  not  sufficient  knowledge  of  the  struc- 
ture of  the  oxides  of  nitrogen  to  make  any  positive  statement  as  to  the  valence 
of  nitrogen  in  them. 

The  structure  of  the  nitrogen  acids  may  be  represented  thus  : 

N  — OH 
Hyponitrous  acid,  N  —  OH,  or  possibly  II  ^ 

Nitrous  acid,  O  =  N  — -  OH,  or  N\OH 

//O 
Nitric  acid,  °^N  —  OH,  or 


Nitrogen  tetroxide,  at  low  temperature,  has  the   formula  N2O4,  but  at 
elevated  temperatures  this   splits  up  into  2NO2,  to  form  again  N2O4,  when 
the  temperature  is  decreased.      There  are  many  other   cases    like 
chemistry. 


172  N OX-METALS  AND   THEIR  COMBINATIONS. 

Such  a  decomposition  which  proceeds  at  high  temperatures,  while  at  lower  ones 
the  constituents  can  recombine,  is  called  dissociation. 

When  electric  sparks  pass  through  atmospheric  air  some  ozone  is  generated 
which  oxidizes  nitrogen,  forming  first  the  lower  and  then  also  the  higher 
oxides;  these  combine  with  water  to  form  nitrous  and  nitric  acid,  which  acids 
are  taken  up  by  the  ammonia  present  in  the  air,  forming  the  respective 
ammonium  salts. 

Nitrogen  monoxide,  N2O  (sometimes  called  nitrous  oxide ; 
also  laughing  gas).  This  compound  was  discovered  by  Priestley  in 
1776;  its  anaesthetic  properties  were  first  noticed  in  1800  by  Sir 
Humphry  Davy,  and  it  was  first  used  in  dentistry  by  Dr.  Horace 
Wells,  a  dentist  of  Hartford,  Conn.,  in  1844.  It  may  be  easily 
obtained  by  heating  ammonium  nitrate  in  a  flask  at  a  temperature 
not  exceeding  250°  C.  (482°  F.),  when  the  salt  is  decomposed  into 
nitrogen  monoxide  and  water : 

NH<NO3  =  2H,O  +  N3O. 

When  nitrous  oxide  is  prepared  for  use  as  an  anesthetic  it  should 
be  passed  through  two  wash-bottles  containing  caustic  soda  and  ferrous 
sulphate  respectively ;  these  agents  will  retain  any  impurities  that  may 
be  formed  during  the  decomposition,  especially  from  an  impure  salt 

Ammonium  nitrate  to  be  used  for  generating  pure  nitrous  oxide  should  be 
completely  volatilized  when  heated  on  platinum  foil ;  its  solution  in  water 
should  not  be  rendered  turbid  by  silver  nitrate,  as  this  would  indicate  the 
presence  of  chlorides.  These  latter  are  objectionable  because  gaseous  com- 
pounds of  chlorine  with  the  oxides  of  nitrogen  may  be  formed.  If  the  gas  is 
prepared  as  directed  above,  it  can  be  used  with  safety. 

Impurities  found  in  the  gas  when  not  properly  made  are  air,  nitric  oxide, 
chlorine,  chloronitrous  and  chloronitric  oxides. 

If  the  gas  is  stored  over  water,  considerable  loss  is  experienced  on  account 
of  the  solubility  of  nitrous  oxide  in  cold  water.  This  loss  can  be  diminished 
by  using  hot  water  or  a  concentrated  solution  of  common  salt  in  water,  both  of 
which  liquids  dissolve  less  of  the  gas. 

Experiment  8.  Use  apparatus  as  represented  in  Fig.  37,  page  140.  Place  in  the 
dry  flask  about  10  grammes  of  ammonium  nitrate,  apply  heat,  collect  the  gas 
in  cylinders  over  water,  and  verify  by  experiments  and  observations  the  correct- 
ness of  the  statements  below  regarding  the  physical  and  chemical  properties 
of  nitrogen  monoxide. 

Nitrogen  monoxide  is  a  colorless,  almost  inodorous  gas,  of  dis- 
tinctly sweet  taste.  It  supports  combustion  almost  as  energetically 
as  oxygen,  but  differs  from  this  element  by  its  solubility  in  cold  water, 
which  absorbs  nearly  its  own  volume.  Under  a  pressure  of  about 
50  atmospheres  it  condenses  to  a  colorless  liquid,  the  boiling-point  of 
which  is  at  about  -90°  C.  (-130°  F.)  and  the  freezing-point  at 
-102°  C.  (-151.6°  F.). 


NITROGEN.  173 

When  inhaled  it  causes  exhilaration,  intoxication,  anaesthesia,  and, 
finally,  asphyxia.  The  gas  is  used  in  dentistry  as  an  anesthetic,  the 
liquefied  compound  being  sold  for  this  purpose  in  wrought-iron 
cylinders.  There  are  two  sizes  of  these  cylinders  :  the  smaller  con- 
tain about  one  and  a  half  pounds  of  the  liquid,  equal  to  100  gallons 
of  gas;  the  larger  size  contains  about  five  times  that  quantity. 

Nitric  oxide,  NO.  This  is  a  colorless  gas  which  is  formed  gener- 
ally when  nitric  acid  acts  upon  metals  or  upon  substances  which 
deoxidize  it.  It  is  capable  of  combining  directly  with  one  or  more 
atoms  of  oxygen,  thereby  forming  nitrogen  tetroxide,  called  nitrogen 
peroxide,  NO2  or  N2O4,  which  is  a  gas  of  deep  red  color  and  poison- 
ous properties.  Nitrogen  trioxide,  N2O3,  exists  as  an  indigo-blue 
liquid  at  temperatures  below  —21°  C.  (-6°  F.);  above  this  tem- 
perature it  decomposes  into  NO  and  NO2. 

Experiment  9.  Use  apparatus  as  shown  in  Fig.  38.  Put  about  20  grammes 
of  copper  or  brass  turnings  into  the  flask  and  pour  through  the  funnel  tube  a 
mixture  of  30  c.c.  concentrated  nitric  acid  and  50  c.c.  water.  Apply  gentle 
heat  and  collect  several  bottles  of  gas.  ^Note  that  the  gas.  in  the  flask  is  at 
first  colored.  Why?  Remove  the  cover  from  a  bottle  of  the  gas,  and  explain 
the  result.  Insert  a  stick  with  a  flame  into  another  bottle  of  the  gas,  and  com- 
pare with  the  action  of  nitrous  oxide.  If  copper  is  used,  filter  the  solution 
after  all  copper  is  dissolved,  and  evaporate  to  get  blue  crystals  of  copper 
nitrate.  For  explanation  of  the  reaction,  see  below,  under  Nitric  Acid. 

Hyponitrous  acid,  HNO,  or  possibly  H2N202,  is  a  very  unstable  white, 
flaky  solid.  Neither  the  acid,  nor  its  salts,  the  hyponitrifces,  are  of  practical 
interest. 

Nitrous  acid,  HNO2,  has  not  been  obtained  in  a  pure  state,  but 
exists  in  solution.  Several  of  its  salts,  the  nitrites,  are  well  known 
and  are  used  analytically  and  otherwise.  Nitrous  acid  very  readily 
breaks  down  into  water  and  its  anhydride,  N2O3,  which  escapes  as 
brown  fumes  from  the  solution.  Hence,  the  salts  of  the  acid  are 
decomposed  by  nearly  all  other  acids.  Nitrous  acid  acts  as  an  oxid- 
izing agent  toward  some  substances,  being  itself  reduced  to  lower 
oxides,  and  as  a  reducing  agent  toward  others,  being  then  oxidized  to 
nitric  acid.  A  solution  of  nitrous  acid  in  water  or  other  acids  has  a 
pale  blue  color. 

Tests  for  nitrous  acid  and  nitrites. 
(Use  about  a  5  per  cent,  solution  of  sodium  or  potassium  nitrite.) 
1.  To  5  c.c.  of  the  solution,  add  a  little  strong  sulphuric  acid.     Note 
the  colored  fumes  and  effervescence  and  the  bluish  color  of  the  liquid. 


174  NON-METALS  AND   THEIR   COMBINATIONS. 

2.  To  the  same  amount  of  the  solution,  add  some  acidified  solution 
of  potassium   permanganate,   which   is   decolorized  at  once.     What 
becomes  of  the  nitrite  ? 

3.  Carry  out  the  directions  of  Test  1,  under  Hydrogen  Dioxide, 
using  a  few  drops  of  the  nitrite  solution  in  place  of  the  hydrogen 
dioxide.     Note  that  the  blue  color  is  not  developed  until  an  acid  is 
added.     Only  free  nitrous  acid  acts  on  potassium  iodide  : 

HN02  +  HI  ==  H20   +   NO  +   I. 
This  is  a  very  delicate  test,  but  not  decisive  alone. 

4.  Dilute  1   drop  of  the  nitrite   solution  in   half  a  beakerful   of 
water,  add  1  c.c.  of  meta-phenylene-diamine  reagent  (see  Nitrous  Acid, 
under  Water  Analysis,  at  end   of  chapter  38).     A  yellow  to  dark 
brown  color  is  produced,  according  to  the  proportion  of  nitrite.     The 
test  is  used  only  for  very  small  amounts  of  nitrite. 

Test  1  is  usually  sufficient  to  recognize  a  nitrite. 

Nitric  acid,  Acidum  nitricum,  HNO3  ;  NO2OH,  =  62.57  (Aqua 
fortis).  Nitrogen  pentoxide,  N2O5,  a  white,  solid,  unstable  compound, 
is  of  scientific  interest  only.  Whjsn  brought  in  contact  with  water  it 
readily  combines  with  it,  forming  nitric  acid  : 

N2O5  +  H20  =  2HNO3. 

The  usual  method  for  obtaining  nitric  acid  is  the  decomposition  of 
sodium  nitrate  by  sulphuric  acid  : 


NaNO3  +  H2SO4  ==    HNO3  +  HNaSO4; 

Sodium 
bisulphate. 

or 

2NaNO3  +  H2SO.  =  2HNO3  +  Na^SO,. 

Sodium 
sulphate. 

At  the  present  time  nitric  acid  is  produced  also  from  the  atmosphere  by 
causing  the  nitrogen  and  oxygen  to  unite  under  the  influence  of  electric  dis- 
charges. The  nitrogen  tetroxide  formed,  when  dissolved  in  water,  gives  nitric 
acid  and  nitric  oxide  : 

3N02  +   H20  ==  2HN03  +   NO. 

The  NO  unites  with  oxygen  to  give  N02,  which  is  again  dissolved.  The  com- 
mercial success  of  this  method  depends  upon  the  cost  of  electric  power.  It  is 
interesting  as  offering  a  source  of  nitrates  when  the  native  supply  shall  have 
been  exhausted. 

Experiment  10.  Prepare  an  apparatus  as  shown  in  Fig.  40.  Heat  in  a  retort  of 
about  250-c.c.  capacity  a  mixture  of  about  50  grammes  of  potassium  nitrate 


NITROGEN.  175 

and  nearly  the  same  weight  of  sulphuric  acid.  Nitric  acid  is  evolved  and  distils 
over  into  the  receiver,  which  is  to  be  kept  cool  during  the  operation  by  pouring 
cold  water  upon  it  or  by  surrounding  it  with  pieces  of  ice.  Examine  the 
properties  of  nitric  acid  thus  made,  and  use  it  for  the  tests  mentioned  below. 
How  much  pure  nitric  acid  can  be  obtained  from  50  grammes  of  potassium 
nitrate?  Weigh  the  acid  which  you  obtain  in  the  experiment  and  compare 
this  weight  with  the  theoretical  quantity. 

Nitric  acid  is  an  almost  colorless,  fuming,  corrosive  liquid,  of 
a  peculiar,  somewhat  suffocating  odor,  and  a  strongly  acid  reaction. 
When  exposed  to  sunlight  it  assumes  a  yellow  or  yellowish-red 
color  in  consequence  of  its  decomposition  into  nitrogen  tetroxide, 
water,  and  oxygen. 

Common  nitric  acid,  of  a  specific  gravity  1.403  at  25°  C.,  is  com- 
posed of  68  per  cent,  of  HNO3  and  32  per  cent,  of  water.  The  diluted 
nitric  acid  of  the  U.  S.  P.  is  made  by  mixing  ten  parts  by  weight  of 
the  common  acid  with  fifty-eight  parts  of  water,  and  contains  10  per 
cent,  of  absolute  nitric  acid ;  it  has  a  specific  gravity  of  1.054  at 
25°  C. 

Fuming  nitric  add  has  a  brown-red  color,  due  to  nitrogen  tetroxide, 
and  emits  vapors  of  the  same  color.  Specific  gravity  1.45  to  1  50. 

FIG.  40. 


Distillation  of  nitric  acid. 


Nitric  acid  is  completely  volatilized  by  heat ;  it  stains  animal  matter 
distinctly  yellow  and  destroys  the  tissue ;  it  is  a  monobasic  acid,  form- 
ing salts  called  nitrates.  These  salts  are  all  soluble  in  water,  for 
which  reason  nitric  acid  cannot  be  precipitated  by  any  reagent. 


176  NON-METALS  AND   THEIR   COMBINATIONS. 

Nitric  acid  is  a  strong  oxidizing  agent ;  this  means  that  it  is  capable 
of  giving  off  part  of  its  oxygen  to  substances  having  affinity  for  it. 

Nitric  acid  of  68  per  cent,  has  a  constant  boiling-point  and  distils  un- 
changed. A  more  concentrated  acid  decomposes  in  part  when  distilled, 
2HNO3  =  2NO2  4-  H20  +  O,  while  a  more  dilute  acid  gives  off  water  at  first. 
In  either  case,  repeated  distillation  gives  a  68  per  cent.  acid. 

The  action  of  nitric  acid  upon  such  metals  as  copper,  silver,  and  many  others 
involves  two  changes,  viz. :  displacement  of  the  hydrogen  of  the  acid  by  the 

metal : 

Cu  +  2HNO3  =  Cu(NO3)2  +  2H; 

and  the  deoxidation  of  another  portion  of  nitric  acid  by  the  liberated  hydrogen 
while  yet  in  the  nascent  state.    Thus  : 

HNO3  +  3H  =  2H2O  +  NO. 

The  liberated  nitrogen  dioxide,  which  is  colorless,  readily  absorbs  oxygen 
from  the  air,  forming  red  vapors  of  nitrogen  tetroxide. 

Another  explanation  of  the  chemical  action  of  nitric  acid  on  metals  is  based 
on  our  knowledge  of  the  fact  that  nitric  acid  readily  gives  up  part  of  its  oxygen 
to  any  substance  having  affinity  for  it.  Therefore,  it  majjfce  assumed  that  the 
first  action  of  the  acid  on  metals  'is  their  conversion  into  oxides,  which  are 
immediately  changed  into  nitrates,  thus: 

2HN03  +  3Cu  =  3CuO  +  H2O  +  2NO. 
CuO  +  2HNO,=  Cu(NO3)2  +  H2O. 

Tests  for  nitric  acid  or  nitrates. 
(Potassium  nitrate,  KNO3,  may  be  used  as  a  nitrate  ) 

1.  Fairly  strong  nitric  acid  with  copper  turnings  gives  copious  red 
fumes.     Rather  dilute  acid,  however,  has  not  a  very  marked  action, 
even  when  heated,  but  the  action  is  increased  by  the  addition  of  some 
concentrated  sulphuric  acid.     A  nitrate,  dry  or  in  solution,  has  no 
action  on  copper,  but  addition  of  concentrated  sulphuric  acid  (to  set 
free  the  nitric  acid)  causes  evolution  of  red  fumes. 

2.  The  solution  of  a  nitrate,  to  which  a  few  small  pieces  of  ferrous 
sulphate  have  been  added,  will  show  a  reddish-purple  or  black  color- 
ation upon  pouring  a  few  drops  of  strong  sulphuric  acid  down  the 
side  of  the  test-tube,  so  that  it  may  form  a  layer  at  the  bottom  of  the 
tube.     The  black  color  is  due  to  the  formation  of  an  unstable  com- 
pound of  the  composition   2FeSO4.NO.     Free   nitric  acid  also  re- 
sponds to  this  test,  which  is  delicate  and  very  often  used. 

3.  Nitrates  deflagrate  when  heated  on  charcoal  by  means  of  the 
blow-pipe  flame.     The  high  temperature  causes  the  nitrate  to  decom- 
pose and  liberate  oxygen,  which  unites  with  the  charcoal  energetically. 


NITROGEN.  177 

Such  action  is  called  dcf (if/ration.  Other  oxidizing  substances  act 
like  nitrates. 

4.  When  a  few  drops  of  a  solution  of  0.1  gramme  of  diphenylamine 
in  ;")()  c.c.  of  10  per  cent,  sulphuric  acid  are  added  to  a  very  dilute 
solution  of  a  nitrate,  and  then  some  concentrated  sulphuric  acid  is 
carefully  poured  down  the  side  of  the  test-tube,  a  deep  blue  color  is 
produced  at  the  line  of  contact. 

A  similar  reaction  is  also  produced  by  hypochlorites,  chlorates, 
chromium  trioxide,  ferric  salts,  and  similar  oxidizing  agents. 

When  the  test  is  made  with  a  similar  solution  of  pyrogallic  acid 
instead  of  the  diphenylamine  solution,  a  deep  brown  color  is 
produced. 

The  tests  with  diphenylamine  and  pyrogallic  acid  show  1  part  of  nitric 
acid  in  three  and  ten  million  parts  of  water  respectively,  and  are  used  chiefly 
to  detect  traces  of  nitric  acid  in  drinking-water.  As  sulphuric  acid  may  con- 
tain nitric  acid,  the  tests  should  also  be  made  with  the  sulphuric  acid  alone  in 
order  to  prove  its  purity. 

Tests  1  and  2  are  sufficient  to  identify  nitric  acid  or  its  salts.  Nitrites  also 
respond  to  these  tests,  but  they  give  red  fumes  by  merely  adding  a  dilute  acid, 
thus  differing  from  nitrates. 

Poisonous  properties;  antidotes.  Strong  nitric  acid  is  a  corrosive, 
violent  poison.  It  first  stains  the  tissues  with  which  it  comes  in  contact  a 
bright-yellow  color,  and  then  corrodes  them. 

As  an  antidote  in  cases  of  poisoning  by  nitric  acid  a  solution  of  sodium  car- 
bonate, or  a  mixture  of  magnesia  and  water,  milk  of  lime,  or  other  alkalies 
well  diluted  may  be  administered  with  the  view  of  neutralizing  the  acid. 

QUESTIONS. — State  the  physical  and  chemical  properties  of  nitrogen.  Men- 
tion the  principal  constituents  of  atmospheric  air  and  the  quantity  in  which 
they  are  present.  By  what  processes  can  the  four  chief  constituents  of  atmo- 
spheric air  be  determined?  Mention  some  decompositions  by  which  ammonia 
is  generated.  Explain  the  process  of  making  ammonia  water.  State  the 
physical  and  chemical  properties  of  ammonia  gas  and  ammonia  water.  How 
is  nitrogen  monoxide  obtained,  and  what  are  its  properties?  Describe  the 
process  for  making  nitric  acid,  and  give  symbols  for  decomposition.  How 
does  nitric  acid  act  on  animal  matter,  and  what  are  its  properties  generally? 
Give  tests  and  antidote  for  nitric  acid. 
12 


178  NON-METALS  AND  THEIR   COMBINATIONS. 

14.    CARBON.        SILICON.         BORON. 
O  =  12  (11.91).    Si*  =  28.3.     B'»  =  10.9. 

Occurrence  in  nature.  Carbon  is  a  constituent  of  all  organic 
matter.  In  a  pure  state  it  is  found  crystallized  as  diamond  and 
graphite,  amorphous  in  a  more  or  less  pure  condition  in  the  various 
kinds  of  coal,  charcoal,  boneblack,  lampblack,  etc.  As  carbon 
dioxide,  carbon  is  found  in  the  air;  as  carbonic  acid,  in  water;  as 
carbonates  (marble,  limestone,  etc.),  in  the  solid  portion  of  our  earth. 

Properties.  The  three  different  allotropic  modifications  of  carbon 
differ  widely  from  each  other  in  their  physical  properties. 

Diamond  is  the  purest  form  of  carbon,  in  which  it  is  crystallized  in 
regular  octahedrons,  cubes,  or  in  some  figure  geometrically  connected 
with  these.  Diamond  is  the  hardest  substance  known  ;  when  heated 
intensely  in  the  presence  of  oxygen  it  burns,  forming  carbon  dioxide. 

Graphite,  plumbago,  or  black-lead,  is  carbon  crystallized  in  short 
six-sided  prisms ;  it  is  a  somewhat  rare,  dark-gray  mineral,  having 
an  almost  metallic  lustre.  It  feels  soft  and  greasy  between  the  fingers 
and  leaves  a  black  mark  when  drawn  over  a  white  surface.  It  is 
used  to  make  lead  pencils,  and  also  as  a  lubricator,  in  stove  polish, 
as  an  admixture  with  clay  used  for  crucibles,  etc. 

Amorphous  carbon  is  always  a  black  solid,  but  the  hardness  and 
specific  gravity  of  the  different  kinds  of  amorphous  coal  differ  widely. 
Amorphous  carbon  in  the  various  kinds  of  coal  is  the  chief  agent  for 
generating  heat  by  combustion.  In  the  form  of  lamp-black  it  is  used 
in  printer's  ink ;  in  bone-black  it  serves  for  decolorizing  sugar  syrups 
and  other  liquids. 

Neither  form  of  carbon  is  soluble  in  any  of  the  common  solvents, 
but  it  dissolves  to  some  extent  in  melted  iron.  On  cooling,  under 
ordinary  conditions,  most  of  the  dissolved  carbon  separates  in  the 
form  of  graphite ;  when  cooling  takes  place  under  high  pressure 
small  diamond-like  crystals  may  be  obtained.  By  the  intense  heat 
produced  by  electricity  carbon  becomes  softened  and  in  small  quan- 
tities also  volatilized. 

Carbon  is  a  quadrivalent  element ;  it  has  little  affinity  for  metals, 
though  at  high  temperatures  it  combines  with  many,  forming  com- 
pounds, termed  carbides.  It  does  not  enter  into  combination  with 
oxygen  at  ordinary  temperature,  but  at  red  heat  it  combines  eagerly 
with  free  or  combined  oxygen,  serving  in  many  cases  as  a  deoxidizing 
agent.  Compounds  of  carbon  with  other  non-metallic  elements  are 
mostly  formed  by  indirect  processes. 


CARBON,   SILICON,   BORON.  179 

Carbon  compounds.  The  chemistry  of  the  carbon  compounds  is 
very  extensive  and  intricate.  There  are  more  compounds  containing 
carbon  than  the  total  of  all  other  compounds,  and  for  good  reasons 
they  are  ptudied  in  a  subdivision  of  chemistry,  called  Organic  Chem- 
istry. A  few  simple  compounds  are  taken  up  in  Inorganic  Chem- 
istry because  of  their  similarity  in  properties  to  the  other  inorganic 
compounds.  These  are  the  two  oxides  of  carbon,  the  carbonates, 
carbon  disulphide,  and  sometimes  the  cyanides  and  sulphocyanates. 

Nearly  all  animal  and  vegetable  substances  contain  carbon,  and 
when  heated  they  usually  undergo  decomposition  and  char,  that  is, 
leave  a  residue  of  black  carbon.  This  is  because  the  other  elements 
go  off  first  in  various  combinations,  while  carbon  remains  last.  But 
some  of  the  carbon  also  passes  off  as  volatile  products.  If  the  heat 
is  high  enough  and  air  has  access,  the  carbon  finally  disappears  or,  as 
is  said,  the  substance  burns  up.  Carbon  compounds  that  are  volatile 
when  heated  do  not  char.  For  example,  alcohol,  ether,  chloroform, 
and  many  others  simply  vaporize  when  heated,  although  they  contain 
carbon.  Carbon  may  be  shown  to  be  present  in  such  compounds  by 
burning  them  in  the  air  (when  combustible)  under  a  funnel  and  draw- 
ing the  products  through  lime-water,  or  by  causing  the  vapors  to  come 
in  contact  with  copper  oxide  heated  to  redness  in  a  tube  and  passing 
the  products  through  lime-water.  When  carbon  compounds  are 
burned  up,  either  in  air  or  by  oxidizing  agents,  as  copper  oxide,  the 
carbon  passes  off  as  gaseous  carbon  dioxide,  CO2,  which  unites  with 
lime-water  to  form  insoluble  white  calcium  carbonate.  In  fact,  this 
is  the  only  common  gas  which  acts  in  this  way  with  lime-water. 

When  carbon  compounds  containing  non-volatile  metals  are 
charred,  the  metals  remain  as  carbonates  or  oxides  mixed  with  the 
residue  of  carbon.  Many  carbon  compounds  char  when  heated  with 
concentrated  sulphuric  acid  because  the  acid  extracts  hydrogen  and 
oxygen  in  the  proportions  to  form  water,  for  which  it  has  a  powerful 
affinity,  thus  leaving  a  residue  of  carbon. 

Experiment  11.  a.  Heat  a  little  starch  on  charcoal  with  the  blow-pipe 
flame.  Note  that  it  blackens  and  burns  up  completely. 

6.  Heat  a  small  knifepointful  of  sugar  in  a  dry  test-tube,  gradually  increas- 
ing the  temperature.  Note  the  melting,  browning  condensation  of  water  on 
the  walls  of  the  tube,  odor,  and  final  charring. 

c.  Heat  gradually  a  little  Eochelle  salt  (K.Na.C4H4O6)  in  a  porcelain  cru- 
cible held  in  a  triangle.  The  salt  melts,  effervesces,  evolves  inflammable 
vapors,  and  chars.  Heat  finally  to  redness,  cool,  and  add  some  dilute  acid. 
Any  effervescence  ?  Explain.  Make  the  same  experiment  with  tartaric  acid. 
Note  any  difference  in  results.  Note  also  the  odor  while  heating. 


180  NON-METALS  AND   THEIR  COMBINATIONS. 

d.  Insert  a  burning  stick  of  wood  into  a  pint  bottle  or  flask,  mouth  down, 
until  flame  is  extinguished  ;  then  remove  the  stick  (is  it  charred?),  pour  into 
the  bottle  about  50  c.c.  of  lime-water  and  shake  it.     Explain  results. 

e.  Heat  slowly  about  2  c.c.  concentrated  sulphuric  acid  in  a  dry  test-tube  with 
a  bit  of  starch,  sugar,  Rochelle  salt,  and  wood    respectively.     Describe  and 
explain  the  results. 

Carbon  dioxide,  CO2.  (Formerly  named  carbonic  acid,  or  anhy- 
drous carbonic  acid.)  This  compound  is  always  formed  during  the 
combustion  of  carbon  or  of  organic  matter ;  also  during  the  decay 
(slow  combustion),  fermentation,  and  putrefaction  (process  of  decom- 
position) of  organic  matter;  it  is  constantly  produced  in  the  animal 
system,  exhaled  from  the  lungs,  and  given  off  through  the  skin. 

Many  spring  waters  contain  considerable  quantities  of  the  gas,  a 
part  of  which  escapes  from  the  water  as  it  rises  to  the  surface. 

By  heating,  many  carbonates  are  decomposed  into  oxides  of  the 
metals  and  carbon  dioxide. 

Lime-burning  is  such  a  process  of  decomposition  : 

CaCO3  =  CaO  -f  CO2. 
Calcium      Calcium 
carbonate,     oxide. 

Another  method  for  the  generation  of  carbon  dioxide  is  the  decom- 
position of  any  carbonate  by  an  acid  : 

CaCO3    +    2HC1  =  CaCl2  +  H2O  +  CO2. 
Calcium     Hydrochloric   Calcium 
carbonate.          acid.          chloride. 

The  reason  the  action  takes  place  readily  and  proceeds  to  completion 
is  because  carbonic  acid  is  only  slightly  soluble  in  water  and  easily 
breaks  up  into  water  and  carbon  dioxide  gas,  which  escapes  and  is 
removed  from  the  field  of  action,  thus  permitting  the  decomposition 
to  be  constantly  renewed.  Almost  any  acid  will  liberate  carbon  di- 
oxide from  a  carbonate.  The  same  principle  is  involved  here  as  in 
the  case  of  the  liberation  of  nitrous  acid  from  nitrites,  nitric  acid 
from  nitrates,  sulphurous  acid  from  sulphites,  or  hydrochloric  acid 
from  chlorides.  (See  Reversible  Actions,  p.  114.) 

Experiment  12.  Use  apparatus  represented  in  Fig.  38,  page  146.  Place  about 
20  grammes  of  marble,  CaCO3,  in  small  pieces  (sodium  carbonate  or  any  other 
carbonate  may  be  used)  in  the  flask,  cover  it  with  water,  and  add  hydrochloric 
acid  through  the  funnel-tube.  The  escaping  gas  may  be  collected  over  water, 
as  in  the  case  of  hydrogen,  or  by  downward  displacement,  i.  e.,  by  passing  the 
delivery-tube  to  the  bottom  of  a  tube  or  other  suitable  vessel,  when  the  carbon 
dioxide,  on  account  of  its  being  heavier  than  atmospheric  air,  gradually  dis- 
places the  latter.  This  will  be  shown  by  examining  the  contents  of  the  vessel 
with  a  burning  taper,  which  is  extinguished  as  soon  as  most  of  the  air  has 
been  expelled. 


CARBON,  SILICON,   BO  RON.  181 

Examine  the  gas  for  its  high  specific  gravity  by  pouring  it  from  one  vessel 
into  another ;  for  its  power  of  extinguishing  flames,  by  mixing  it  with  an  equal 
volume  of  air,  which  mixture  will  be  found  not  to  support  the  combustion  of 
a  taper  notwithstanding  that  oxygen  is  contained  in  it.  Add  to  one  portion  of 
the  collected  gas  some  lime-water,  shake  it,  and  notice  that  it  becomes  turbid. 
Blow  air  exhaled  from  the  lungs  through  a  glass  tube  into  lime-water,  and 
notice  that  it  also  turns  turbid. 

Continue  to  pass  the  gas  through  the  turbid  liquid,  and  notice  that  it  becomes 
clear  in  consequence  of  the  dissolving  action  of  carbonic  acid  water  on  calcium 
carbonate.  On  heating  the  solution  carbon  dioxide  is  expelled  and  calcium 
carbonate  is  reprecipitated.  (So-called  "  hard  "  waters  often  contain  calcium 
carbonate  dissolved  by  carbonic  acid.  On  heating  these  hard  waters  they 
become  "soft,"  because  the  dissolved  carbonate  is  precipitated.) 

If  marble  has  been  used  for  the  experiment,  neutralize  the  liquid  in  the  flask, 
if  acid,  by  adding  more  marble  until  action  ceases,  filter,  and  evaporate  it  in  a 
dish  to  dry  ness.  The  solid  residue  is  a  salt,  calcium  chloride.  Expose  some 
of  it  to  the  air  for  a  long  time  and  note  that  it  absorbs  moisture  or  deliquesces. 
What  method  of  salt  formation  is  illustrated  by  this  experiment? 

If  sodium  carbonate  has  been  used,  neutralize  the  liquid  by  adding  acid 
or  carbonate,  as  may  be  required,  filter,  and  evaporate  it  to  dryness.  Taste 
the  residue.  What  is  it  ?  Taste  also  sodium  carbonate  and  the  acid. 

Carbon  dioxide  is  a  colorless,  odorless  gas,  having  a  faintly  acid 
taste.  By  a  pressure  of  38  atmospheres,  at  a  temperature  of  0°  C. 
(32°  F.),  carbon  dioxide  is  converted  into  a  colorless  liquid,  which  by 
intense  cold  ( — 79°  C.,  — 110°  F.)  may  be  converted  into  a  white, 
solid,  crystalline,  snow-like  substance.  The  specific  gravity  of  carbon 
dioxide  is  1.529 ;  it  is  consequently  about  one-half  heavier  than 
atmospheric  air.  One  liter  at  0°  C.  and  760  mm.  pressure  weighs 
1.977  grammes. 

Cold  water  absorbs  at  the  ordinary  pressure  about  its  own  volume 
of  carbon  dioxide,  but  the  solubility  is  increased  one  volume  for  every 
increase  of  one  atmosphere  in  pressure  (soda  water). 

Carbon  dioxide  is  not  combustible,  and  not  a  supporter  of  combus- 
tion ;  on  the  contrary,  it  has  a  decided  tendency  to  extinguish  flames, 
air  containing  one-tenth  of  its  volume  of  carbon  dioxide  being  unable 
to  support  the  combustion  of  a  candle.  While  not  poisonous  when 
taken  into  the  stomach,  carbon  dioxide  acts  indirectly  as  a  poison 
when  inhaled,  because  it  cannot  support  respiration,  and  prevents, 
moreover,  the  proper  exchange  between  the  carbon  dioxide  of  the 
blood  and  the  oxygen  of  the  atmospheric  air. 

Common  atmospheric  air  contains  about  4  volumes  of  carbon 
dioxide  in  10,000  of  air,  or  0.04  per  cent.  In  the  process  of  respira- 
tion this  air  is  inhaled,  and  a  portion  of  the  oxygen  is  absorbed  in 
the  lungs  by  the  blood,  which  conveys  it  to  the  different  portions  of  the 


182  NON-METALS  AND   THEIR   COMBINATIONS. 

animal  body,  and  receives  in  exchange  for  the  oxygen  a  quantity  of 
carbon  dioxide,  produced  by  the  union  of  a  former  supply  of  oxygen 
with  the  carbon  of  the  different  organs  to  which  the  blood  is  supplied. 
The  air  issuing  from  the  lungs  contains  this  carbon  dioxide,  in 
quantity  about  4  volumes  in  100  of  exhaled  air,  which  is  100  times 
more  than  contained  in  fresh  air. 

Exhaled  air  is,  moreover,  contaminated  by  other  substances  than  carbon 
dioxide,  such  as  ammonia,  hydrocarbons,  and  most  likely  traces  of  other  or- 
ganic bodies,  the  true  nature  of  which  has  not  been  fully  recognized,  but  which 
seem  to  be  directly  poisonous.  The  bad  effects  experienced  in  breathing  air 
which  has  become  contaminated  by  the  exhalations  from  the  lungs,  are  most 
likely  due  to  these  unknown  bodies.  As  we  have  as  yet  no  methods  of  ascer- 
taining the  quantity  of  these  poisonous  substances  present  in  exhaled  air,  the 
determination  of  the  amount  of  exhaled  carbon  dioxide  present  must  serve  as 
an  indicator  of  the  fitness  of  an  air  for  breathing  purposes.  As  a  general  rule, 
it  may  be  stated  that  it  is  not  advisable  to  breathe,  for  any  length  of  time,  air 
containing  more  than  0.1  per  cent,  of  exhaled  carbon  dioxide;  in  air  contain- 
ing 0.5  per  cent,  most  persons  are  attacked  by  headache,  still  larger  quantities 
produce  insensibility,  and  air  containing  8  per  cent,  of  carbon  dioxide  causes 
death  in  a  few  minutes. 

As  exhaled  air  contains  from  3.5  to  4  per  cent,  of  carbon  dioxide,  it  is  unfit 
to  be  breathed  again..  The  total  amount  of  carbon  dioxide  evolved  by  the 
lungs  and  skin  of  a  grown  person  amounts  to  about  0.7  cubic  foot  per  hour. 
Hence  the  necessity  for  a  constant  supply  of  fresh  air  by  ventilation.  This 
becomes  the  more  necessary  where  an  additional  quantity  of  carbon  dioxide  is 
supplied  by  illuminating  flames. 

Mentioned  above  are  many  processes  by  which  carbon  dioxide  is 
constantly  produced  in  nature,  and  we  might  assume  that  the  amount 
of  0.04  per  cent,  of  carbon  dioxide  contained  in  atmospheric  air 
would  gradually  increase.  This,  however,  is  not  the  case,  because 
plants,  and  more  especially  all  their  green  parts,  are  capable  of  ab- 
sorbing carbon  dioxide  from  the  air,  while  at  the  same  time  they 
liberate  oxygen. 

This  process  of  vegetable  respiration  (if  we  may  so  call  it),  which 
takes  place  under  the  influence  of  sunlight,  is,  consequently,  the 
reverse  of  that  of  animal  respiration.  The  animal  uses  oxygen  and 
liberates  carbon  dioxide ;  the  plant  consumes  this  carbon  dioxide  and 
liberates  oxygen. 

Carbon  dioxide  is  an  acid  oxide,  which  combines  with  water,  form- 
ing carbonic  acid  : 

CO2  +  H2O  =  H2CO3. 

Carbonic  acid,  H2CO3,  CO(OH)2>  is  not  known  in  a  pure  state,  but 
always  diluted  with  much  water,  as  in  all  the  different  natural  waters. 


CARBON,   SILICON,   BORON.  183 

Carbonic  acid  is  a  dibasic,  extremely  weak  acid,  the  salts  of  which  are 
known  as  carbonates.  Many  of  these  carbonates  (calcium  carbonate, 
for  instance)  are  abundantly  found  in  nature.  Only  the  alkali  car- 
bonates and  bicarbonates  are  soluble  in  water.  Acid  carbonates  of 
some  other  metals,  such  as  magnesium,  calcium,  zinc,  iron,  are  also 
slightly  soluble  in  water,  but  these  do  not  exist  in  the  dry  state.  The 
bicarbonates  when  heated  to  about  100°  C.  give  up  carbon  dioxide 
and  form  carbonates  : 

2NaHCO3    =    Na2CO3    -f    H2O    -f    CO^ 
At  high  temperatures  only  alkali  carbonates  are  not  decomposed. 

Tests.  Since  nearly  all  carbonates  are  insoluble  in  water,  these 
are  formed  as  precipitates  whenever  a  solution  of  an  alkali  carbonate 
(those  of  potassium,  sodium,  or  ammonium)  is  added  to  a  solution  of 
a  salt  of  any  other  metal.  This  is  a  corroborative  test  for  a  soluble 
carbonate,  but  the  best  and  decisive  test  for  all  carbonates  and  car- 
bonic acid  is  found  in  Experiment  12,  namely,  the  liberation  of 
carbon  dioxide  and  its  action  on  lime-water. 

Carbon  monoxide,  carbonic  oxide,  CO.  While  carbon,  as  a 
general  rule,  is  quadrivalent,  in  this  compound  it  exerts  a  valence  of 
2.  Carbon  monoxide  is  a  colorless,  odorless,  tasteless,  neutral  gas, 
almost  insoluble  in  water  ;  it  burns  with  a  pale-blue  flame,  forming 
carbon  dioxide  ;  it  is  very  poisonous  when  inhaled,  forming  with  the 
coloring  matter  of  the  blood  a  compound  which  prevents  the  absorp- 
tion of  oxygen.  Carbon  monoxide  is  formed  when  carbon  dioxide  is 
passed  over  red-hot  coal  : 

C02  +  C  =  2CO. 

The  conditions  necessary  for  the  formation  of  carbon  monoxide  are, 
consequently,  present  in  any  stove  or  furnace  where  coal  burns  with 
an  insufficient  supply  of  air.  The  carbon  dioxide  formed  in  the  lower 
parts  of  the  furnace  is  decomposed  by  the  coal  above.  The  blue 
flames  frequently  playing  over  a  coal  fire  are  burning  carbon  mon- 
oxide. This  gas  is  formed  also  by  the  decomposition  of  oxalic  acid 
(and  many  other  organic  substances)  by  sulphuric  acid  : 
H2C2O4  +  H2SO4  =  H2SO,.H2O  +  CO2  +  CO. 


Oxalic  Sulphuric 

acid.  acid. 


Carbon  monoxide  is  now  manufactured  on  a  large  scale  by  causing  the  de- 
composition of  steam  by  coal  heated  to  red  heat.     The  decomposition  takes 

place  thus: 

H20  +  C  ==  2H  +  CO. 


184  NON-METALS  AND   THEIR   COMBINATIONS. 

The  gas  mixture  thus  obtained,  known  as  water-gas,  may  be  used  for  heating 
purposes  directly,  but  has  to  be  mixed  with  hydrocarbons  when  used  as  an 
illuminating  agent,  for  reasons  which  will  be  pointed  out  below  when  consider- 
ing the  nature  of  flames. 

Carbonyl  chloride,  COC12.  This  is  formed  when  a  mixture  of  carbon 
monoxide  and  chlorine  is  exposed  to  sunlight,  and,  hence,  is  also  known  as 
phosgene.  Commercially  it  is  made  by  passing  a  mixture  of  the  two  gases  over 
animal  charcoal,  which  acts  as  a  catalytic  agent.  Carbonyl  chloride  is  gas- 
eous above  8°  C.,  has  a  suffocating  odor,  and  dissolves  readily  in  benzene. 
Water  decomposes  it  at  once  into  carbonic  and  hydrochloric  acids,  COC12  + 
2H2O  =  H2C03  H-  2HC1.  It  is  used  in  making  certain  synthetic  organic 
compounds.. 

Compounds  of  carbon  and  hydrogen.  There  are  no  other  two 
elements  which  are  capable  of  forming  so  large  a  number  of  different 
combinations  as  are  carbon  and  hydrogen.  Several  hundred  of  these 
hydrocarbons  are  known,  and  their  consideration  belongs  to  the 
domain  of  organic  chemistry. 

Two  of  these  hydrocarbons,  however,  may  be  briefly  mentioned, 
as  they  are  of  importance  in  the  consideration  of  common  flames. 
These  compounds  are:  methane  (marsh-gas,  fire-damp),  CH4;  and 
efhene  (olefiant  gas),  C2H4. 

Both  compounds  are  colorless,  almost  odorless  gases,  and  both  are 
products  of  the  destructive  distillation  of  organic  substances.  De- 
structive distillation  is  the  heating  of  non-volatile  organic  substances 
in  such  a  manner  that  the  oxygen  of  the  atmospheric  air  has  no  access, 
and  to  such  an  extent  that  the  molecules  of  the  organic  matter  are 
split  up  into  simpler  compounds.  Among  the  gaseous  products 
formed  by  this  operation,  more  or  less  of  the  two  hydrocarbons 
mentioned  above  is  found. 

Marsh-gas  is  formed  frequently  by  the  decomposition  of  organic 
matter  in  the  presence  of  moisture  (leaves,  etc.,  in  swamps) ;  and  dur- 
ing the  formation  of  coal  in  the  interior  of  the  earth  the  gas  often 
gives  rise  to  explosion  in  coal  mines.  During  these  explosions  of  the 
methane  (mixed  with  air  and  other  gases),  called  fire-damp  by  the 
miners,  carbon  is  converted  into  carbon  dioxide,  which  the  miners 
speak  of  as  choke-damp,  or  after-damp. 

Flame  is  gas  in  the  act  of  combustion.  Of  combustible  gases, 
have  been  mentioned :  hydrogen,  carbon  monoxide,  marsh-gas,  and 
olefiant  gas.  These  four  gases  are  actually  those  which  are  found 
chiefly  in  any  of  the  common  flames  produced  by  the  combustion  o? 
organic  matter,  such  as  paper,  wood,  oil,  wax,  or  illuminating  gas  itself 

These  gases  are  generated  by  destructive  distillation,  the  heat  being 


CARBON,   SILICON,   BORON. 


185 


supplied  either  by  a  separate  process  (manufacture  of  illuminating 
gas  by  heating  wood  or  coal  in  retorts),  or  generated  during  the 
combustion  itself. 

In  burning  a  candle,  for  instance,  fat  is  constantly  decomposed  by 
the  heat  of  the  flame  itself,  the  generated  gases  burning  continuously 
until  all  fat  has  been  decomposed,  and  the  products  of  decomposition 
have  been  burned  up,  i.  e.,  have  been  converted  into  carbon  dioxide 
and  water. 

An  ordinary  flame  (Fig.  41)  consists  of  three  parts  or  cones.  The 
inner  portion  is  chiefly  unburnt  gas  ;  the  second  is  formed  of  partially 
burnt  and  burning  gas  ;  the  outer  cone,  showing  scarcely  any  light,  is 
that  part  of  the  flame  where  complete  combustion  takes  place.  The 
highest  temperature  is  found  between  the  second  and  third  cone. 

The  light  of  a  flame  is  caused  by  solid  particles  of  carbon  heated 
to  a  white  heat.  The  changes  that  take  place  in  a  flame  are  difficult 
to  study,  but  sufficient  has  been  done  experimentally  to  permit  the 
conclusion  to  be  drawn  that  the  separation  of  carbon  in  a  flame  is  due 
to  dissociation  of  some  of  the  hydrocarbons,  of  which  ethylene 
(ethene)  is  the  most  important.  It  is  well  known  that  when  ethylene 
(C2H4)  is  heated  it  yields  acetylene  (C2H2),  which  in  turn  gives  carbon 
and  hydrogen.  Evidence  that  acetylene  is  present  in  a  gas  flame  is 
furnished  by  the  fact  that  when  a  Bunsen  flame  "  strikes 
back,"  that  is,  burns  at  the  base  of  the  tube  so  that 
incomplete  combustion  of  the  gases  takes  place,  a  large 
quantity  of  acetylene  is  formed. 

If  a  sufficient  amount  of  air  be  previously  mixed  with 
the  illuminating  gas,  as  is  done  in  the  Bunsen  burner,  no 
separation  of  carbon  takes  place,  and,  therefore,  no  light 
is  produced,  but  a  more  intense  heat  is  generated.      A 
similar  effect  is  produced  by  the  aid  of  the  blow-pipe  or 
by  means  of  the  blast  lamp,  which  serve  to  direct  a  cur- 
rent of  air   directly  into   the  cone  of  the   flame.     The 
luminous   and    non-luminous    Bunsen  flame,  using  the 
same  flow  of  gas,  must  produce  the  same  amount  of  heat 
for   a    definite    amount   of  gas   burned,  since  the  end- 
products  of  combustion    are   the   same   in   both  cases. 
But  the  non-luminous  flame  is  much  shorter  than  the 
luminous  one,  and  thus  the  heat  is  concentrated   within   a  smaller 
space,  and,  therefore,  the  temperature  is  much  higher  than  in  the 
luminous  flame. 
*  The  cause  of  non-luminosity  of   a  flame  when  air  or  oxygen  is 


FIG.  41. 


Structure  of 
flame. 


186  NON-METALS  AND   THEIR  COMBINATIONS. 

admitted  into  the  interior,  as  in  a  Bunsen  burner,  is  difficult  to  explain. 
That  it  is  due  to  other  causes  than  the  presence  of  the  oxygen  is  shown 
bv  the  fact  that  nitrogen  or  carbon  dioxide  will  also  destroy  luminosity. 
The  introduction  of  cold  gases  into  a  flame  lowers  the  temperature  of 
the  inner  cone,  where  the  dissociation  of  ethylene  takes  place.  It 
seems  probable  that  this  lowering  of  temperature  and  dilution  of  the 
gases  diminish  the  decomposition  of  ethylene  to  such  an  extent  that 
not  enough  carbon  is  separated  to  give  luminosity. 

Silicon  or  Silicium,  Si  =  28.3,  is  found  in  nature  very  abundantly  as 
silicon  dioxide,  or  silica,  SiO2  (rock-crystal,  quartz,  agate,  sand),  and  in  the 
form  of  silicates,  which  are  silicic  acid  in  which  the  hydrogen  has  been  replaced 
by  metals.  Most  of  our  common  rocks,  such  as  granite,  porphyry,  basalt, 
feldspar,  mica,  etc.,  are  such  silicates  or  a  mixture  of  them.  Small  quantities 
of  silica  are  found  in  spring- waters,  as  well  as  in  vegetable  and  animal  matters. 

Silicon  resembles  carbon  both  in  its  physical  and  chemical  properties.  Like 
carbon,  it  is  known  in  the  amorphous  state,  and  forms  two  kinds  of  crystals, 
which  resemble  graphite  and  diamond.  Like  carbon,  silicon  is  quadrivalent, 
forming  silicon  dioxide,  Si02,  silicic  acid,  H.2SiO3,  silicon  hydride,  SiH4,  silicon 
chloride,  SiCl4,  which  compounds  are  analogous  to  the  corresponding  carbon 
compounds,  C02,  H2CO3,  CH4,  and  CC14. 

The  compounds  formed  by  the  union  of  silicon  with  hydrogen,  chlorine,  and 
fluorine  are  gases.  The  latter  compound,  silicon  fluoride,  SiF4,  is  obtained  by 
the  action  of  hydrofluoric  acid  on  silica  or  silicates,  thus : 

Si03  -f  4HF  =  SiF4  -f  2H2O. 

This  reaction  is  used  in  the  analysis  of  silicates,  which  are  decomposed  and 
rendered  soluble  by  the  action  of  hydrofluoric  acid. 

Silicon  fluoride  is  decomposed  by  water  into  silicic  acid  and  hydrofluosilicic 
acid,  H2SiF6,  thus : 

3SiF4  +  3H2O  =  H2Si03  +  2H2SiF6. 

Several  varieties  of  silicic  acid  are  known,  of  which  may  be  mentioned  the 
normal  silicic  acid,  H4SiO4,  and  the  ordinary  silicic  acid,  H2SiO3,  from  the  latter 
of  which,  by  heating,  water  may  be  expelled,  when  silicon  dioxide,  SiO2,  is  left. 

Tests  for  silicic  acid  and  silicates. 

(Soluble  glass  or  flint  may  be  used.) 

1.  Silicic  acid  and  most  silicates  are  insoluble  in  water  and  acids.     By  fusing 
silicates  with  about  5  parts  of  a  mixture  of  the  carbonates  of  sodium  and  potas- 
sium the  silicates  of  these  metals  (known  as  soluble  glass)  are  formed.     By 
dissolving  this  salt  in  water  and  acidifying  the  solution  with  hydrochloric  acid 
a  portion  of  the  silica  separates  as  the  gelatinous  hydroxide. 

Complete  separation  of  the  silica  is  accomplished  by  evaporating  the  mixt- 
ure to  complete  dryness  over  a  water-bath,  and  re-dissolving  the  chlorides  of 
the  metals  in  water  acidulated  with  hydrochloric  acid ;  silica  remains  undis- 
solved  as  a  white  amorphous  powder. 

2.  Silica  or  silicates  when  added  to  a  bead  of  microcosmic  salt  (see  index) 
form  on  heating  before  the  blowpipe  the  so-called  silica-skeleton. 

Silicon  carbide,  SiO.  (Carborundum,   Carbon  silicide).    This  compound 


CARBON,   SILICON,   BORON.  187 

furnishes  a  typical  illustration  of  the  possibilities  of  the  electric  furnace  for 
manufacturing  purposes.  Figs.  32  and  33,  page  81,  give  a  sectional  and  an 
exterior  view  of  the  furnace  used.  The  current  enters  and  leaves  the  furnace 
through  cables  terminating  in  carbon  electrodes  fastened  in  the  wall.  Between 
them  is  placed  a  core  of  coke,  surrounded  by  a  mixture  of  carbon,  sand,  and 
salt.  The  current  heats  the  mass  to  about  3500°  C.  (6332°  F.),  when  the 
carbon  combines  with  both  elements  of  the  sand,  thus: 

Si02  +  3C  =  2CO  +  SiC. 

Carborundum  forms  beautiful,  dark-green,  iridescent  crystals  of  extreme  hard- 
ness, in  the  latter  quality  being  exceeded  only  by  the  diamond.  It  is  extensively 
used  as  a  polishing  agent,  gradually  replacing  emery,  to  which  it  is  far  superior. 

Boron,  B'"  =  10.9,  is  found  in  but  few  localities,  either  as  boric 
(boracic)  acid  or  sodium  borate  (borax).  Formerly  the  total  supply 
of  boron  was  derived  from  Italy  :  large  quantities  of  borax  are  now 
obtained  from  Nevada  and  California. 

Boron  exists  as  a  greenish  -brown  amorphous  powder  and  also  in  the  form 
of  hard  and  often  highly  lustrous  crystals.  Boron  combines  with  many  of  the 
non-metals,  forming  such  compounds  as  boron  trichloride,  BC13,  trifluoride, 
BF3,  and  hydride,  BH3.  It  is  one  of  the  few  elements  which  at  a  high  tempera- 
ture combine  directly  with  nitrogen,  forming  nitrogen  boride,  BN. 

Boric  acid,  Acidum  boricum,  H3BO3,  B(OH)3  =  61.54  (Boracic 
acid),  is  a  white,  crystalline  substance,  which  is  sparingly  soluble  in 
cold  water  or  alcohol,  but  more  soluble  in  glycerin  ;  it  has  but  weak 
acid  properties.  When  heated  to  100°  C.  (212°  F.)  it  loses  water, 
and  is  converted  into  mdaboric  acid,  HBO2,  which  when  heated  to 
160°  C.  is  converted  into  tetraboric  acid,  H2B4O7,  from  which  borax, 
Na2B4O7  -f  10H2O,  is  derived.  At  a  white  heat  boric  acid  loses  all 
water,  and  is  converted  into  boron  trioxide,  B2O3.  From  a  boiling 
solution  boric  acid  readily  volatilizes  with  the  steam. 

Boric  acid  is  obtained  by  adding  hydrochloric  acid  to  a  hot  satur- 
ated solution  of  borax,  when  boric  acid  separates  on  cooling.  The 
chemical  change  is  this  : 

7  +  2HC1  +  5H2O  =  4H3B03  +  2NaCl. 


It  is  rather  odd  that  while  the  usual  form  of  boric  acid  in  the  uncombined 
state  is  the  orthoboric  acid,  H3BO3,  salts  of  this  form  are  hardly  known.  Salts 
of  metaboric  acid  occur,  but  the  best-known  salts  are  derived  from  tetraboric 
acid,  and  the  best  representative  is  the  sodium  salt,  borax.  On  the  other  hand, 
when  the  acid  is  liberated  from  the  salts,  it  assumes  the  ortho  form.  From  the 
formula  of  tetraboric  acid,  it  appears  that  four  molecules  of  the  ortho  acid  com- 
bine with  elimination  of  water  to  form  a  more  complex  molecule  : 

4H3B03  H2B407    +    5H20. 

There  are  other  cases  of  this  kind,  as  will  be  seen  later. 


188  NON-METALS  AND   THEIR   COMBINATIONS. 

Borax  may  be  looked  upon  as  containing  sodium  metaborate  and  boric 
oxide,  2NaBO2  +  B,O3.  When  it  is  heated  with  basic  oxides,  these  unite  with 
the  excess  of  B2O3>  forming  a  fused  mixed  metaborate.  This  action  explains 
the  use  of  borax  on  hot  metal  surfaces  which  are  to  be  welded.  Some  of  these 
metaborates  have  distinctive  colors.  For  this  reason  borax  beads  are  used  as 
tests  for  certain  metals  (see  under  Sodium  Borate). 

Boric  acid  is  such  a  weak  acid  that  its  solution  has  only  a  slight  action  on 
litmus-paper,  and  it  is  displaced  from  its  salts  by  nearly  every  other  acid.  The 
borates  of  the  alkali  metals  only  are  easily  soluble  in  water,  the  others  being 
either  insoluble  or  nearly  so.  Hence,  when  a  solution  of  an  alkali  borate  (but 
not  of  free  boric  acid)  is  added  to  a  solution  of  a  saltof  other  metals,  a  precipitate 
is  obtained.  Alkali  borates  show  a  strong  alkaline  reaction  to  litmus  because 
they  are  partly  hydrolyzed  in  solution  to  free  alkali  and  boric  acid.  It  will  be 
?een  that  boric  acid  is  very  much  like  carbonic  acid  in  behavior. 

Boric  acid  and  borax  are  practically  the  only  compounds  of  boron  that  are 
used.  Both  are  used  in  medicine  and  as  preservatives.  When  powdered  they 
look  much  alike,  but  can  be  distinguished  by  the  fact  that  the  acid  is  soluble 
in  alcohol  while  borax  is  not,  and  that  borax  has  a  marked  alkaline  reaction  to 
litmus,  and  when  held  in  a  Bunsen  flame  on  platinum  wire  gives  a  yellow  color, 
while  free  boric  acid  gives  a  green  color. 

Tests  for  boric  acid  and  borates. 

1.  When  borax  is  heated  on  the  loop  of  a  platinum  wire  in  a  Bunsen 
flame  it  first  puffs  up  very  much,  and  then  gradually  melts  into  a 
transparent,  colorless  bead.       If  the  bead   is  moistened  with  concen- 
trated sulphuric  acid  and   heated  again,  a  green  color  is  produced. 
Boric  acid  also  melts  into  a  colorless  bead.      Note  any  difference  in 
color  of  the  flame. 

2.  Mix  in  a  porcelain  dish  some  borax  with  2  c.c.  of  concentrated 
sulphuric  acid,  add  about  10  c.c.  of  alcohol,  and  ignite.      The  flame 
has  a  mantle  of  green  color,  which  is  best  seen  by  alternately  extin- 
guishing and  relighting  the  alcohol.     Eepeat  the  experiment,  omitting 
the  acid ;  no  green  color  is  seen.      Free  boric  acid  is  volatilized  with 
alcohol,  but  not  its  salts. 

QUESTIONS.— How  is  carbon  found  in  nature?  State  the  physical  and 
chemical  properties  of  carbon  in  its  three  allotropic  modifications.  Mention 
three  different  processes  by  which  carbon  dioxide  is  generated  in  nature,  and 
some  processes  by  which  it  is  generated  by  artificial  means.  State  the  physical 
and  chemical  properties  of  carbon  dioxide.  Explain  the  process  of  respiration 
from  a  chemical  point  of  view.  What  is  the  percentage  of  carbon  dioxide  in 
atmospheric  air,  and  why  does  its  amount  not  increase  ?  State  the  composition 
of  carbonic  acid  and  of  a  carbonate.  How  can  they  be  recognized  by  analyt- 
ical methods?  Under  what  circumstances  will  carbon  monoxide  form,  and 
how  does  it  act  when  inhaled?  What  is  destructive  distillation,  and  what 
gases  are  generally  formed  during  that  process?  Explain  the  structure  and 
luminosity  of  flames. 


THEORY  OF  ELECTROLYTIC  DISSOCIATION,   ETC.          189 

3.  A  solution  of  boric  acid,  or  of  a  boratc  acidulated  with  dilute 
hydrochloric  acid,  colors  a  strip  of  t turmeric  paper  dark  red,  which 
becomes  more  intense  on  drying.  The  color  is  changed  to  bluish  black 
by  dilute  ammonia  water. 

Sodium  perborate,  NaBO.5.4H.2O.  When  a  mixture  of  248  grammes  of 
boric  acid  and  78  grammes  of  sodium  peroxide  is  gradually  added  to  2  liters  of 
cold  water  a  crystallized  compound  is  obtained.  When  the  latter  in  solution  is 
treated  with  the  proper  proportion  of  an  acid,  sodium  perborate  separates.  It 
is  very  stable  when  dry,  but  in  solution  it  has  all  the  properties  of  a  solution  of 
hydrogen  dioxide.  It  is  a  good  antiseptic  and  deodorant,  and  may  be  applied 
as  a  dusting-powder  or  in  solution. 


15.  THEORY  OF  ELECTROLYTIC  DISSOCIATION,  OR  IONIZATION. 
ELECTROLYSIS.  DISSOCIATION  THEORY  APPLIED  TO  ACIDS, 
BASES,  SALTS,  AND  NEUTRALIZATION. 

Theory  of  Electrolytic  Dissociation. 

It  was  observed  long  ago  tbat  aqueous  solutions  of  certain  kinds 
of  substances,  of  which  cane-sugar  is  a  good  type,  do  not  conduct  an 
electric  current,  while  aqueous  solutions  of  other  substances,  of  which 
common  salt  or  hydrochloric  acid  is  a  good  example,  are  excellent 
conductors  of  electricity.  Moreover,  it  was  also  observed  that  sub- 
stances which  conduct  electricity  in  aqueous  solution  do  not  conduct 
when  they  are  dissolved  in  certain  solvents,  like  benzene,  ether,  chlo- 
roform, etc.  This  fact  evidently  points  to  the  conclusion  that  water 
has  some  peculiar  action  on  some  substances  whereby  they  become 
possessed  of  the  power  to  conduct  a  current.  The  same  kind  of 
effect  is  also  noticed  in  regard  to  chemical  behavior.  For  example, 
dry  hydrochloric  acid  gas  dissolved  in  dry  benzene  neither  conducts 
electricity  nor  has  an  acid  reaction  on  litmus,  nor  appreciably  acts 
on  zinc,  whereas  an  aqueous  solution  of  the  gas  conducts  well,  has  a 
marked  acid  reaction  on  litmus,  and  attacks  zinc  vigorously.  It  appears, 
therefore,  that  hydrochloric  acid  molecules  in  aqueous  solution  must 
be  in  a  state  different  from  that  when  they  are  dissolved  in  benzene. 
It  should  be  noted  that  pure  water  itself  is  not  a  conductor,  nor  are 
the  other  substances  when  dry,  but  their  solutions  in  water  conduct. 
There  are  a  few  other  liquids  which  show  this  property,  but  to  a  far 
less  extent  than  water  does,  to  which  this  discussion  will  be  confined. 

Substances  whose  aqueous  solutions  conduct  electricity  are  known 
as  electrolytes,  those  whose  solutions  do  not  are  called  non-electrolytes. 
It  is  found  experimentally  that  acids,  bases,  and  salts  are  electrolytes, 
and  it  is  precisely  these  substances  whose  aqueous  solutions  show 


190  NON-METALS  AND   THEIR   COMBINATIONS. 

abnormally  large  values  of  freezing-point  depressions,  boiling-point 
elevations,  and  osmotic  pressures.  In  the  discussion  of  the  latter 
subjects  (which  see)  it  is  pointed  out  that  the  abnormally  acting  sub- 
stances behave  as  if  there  are  more  particles  in  solution  than  the 
number  of  molecules  corresponding  to  the  weights  of  the  substances 
dissolved,  which  fact  can  be  accounted  for  only  on  the  supposition 
that  some  molecules  are  decomposed  by  the  solvent  into  smaller  par- 
ticles. Further,  since  molecules  which,  like  those  of  sugar,  act  nor- 
mally in  regard  to  freezing-point,  boiling-point,  and  osmotic  pressure 
phenomena,  and  thus  show  no  indication  of  decomposition  by  the 
solvent,  do  not  conduct  electricity,  it  follows  that  the  fragments  of 
decomposed  molecules  must  be  responsible  for  the  ability  to  conduct 
in  the  case  of  solutions  of  electrolytes.  In  electrolysis  (see  page  82) 
these  fragments  are  the  particles  that  are  attracted  to  the  charged 
poles,  hence  the  further  assumption  is  made  that  the  fragments  (or 
ions  as  they  are  called)  are  themselves  charged  with  electricity,  be- 
cause it  is  known  that  electricity  attracts  only  bodies  that  possess  a 
charge  of  electricity.  Briefly  summed  up,  then,  the  THEORY  OF 
ELECTROLYTIC  DISSOCIATION  assumes  that  molecules  of  electrolytes 
when  dissolved  in  water  break  up  to  a  varying  degree  into  independent 
particles  charged  with  electricity,  and  that  the  nature  and  number  of 
these  charged  particles  determine  to  a  large  degree  certain  physical  and 
chemical  properties  of  solutions. 

This  theory  was  proposed  by  the  Swedish  physicist  Arrhenius  in 
lSS7  •  its  general  adoption  has  been  hastened  by  the  work  of  van't 
Hoff,  Ostwald,  and  Nernst. 

The  dissociation  of  molecules  in  solution  is  also  called  IONIZATION, 
and  the  electrically  charged  particles  are  called  ions.  These  are  al- 
ways of  two  kinds,  namely,  electro-positive  ions,  or  cations,  because 
they  are  attracted  to  the  negative  pole  or  cathode  during  electrolysis, 
and  electro-negative  ions,  or  anions,  because  they  are  attracted  to  the 
positive  pole  or  anode.  Since  solutions  are  themselves  electrically 
neutral,  that  is,  show  no  charge  of  electricity  as  a  whole,  it  follows 
that  the  sum  of  the  electric  charges  of  the  positive  ions  equals  the 
sum  of  the  charges  of  the  negative  ions.  The  two  kinds  of  ions  are 
in  electrical  balance. 

Composition  of  ions.  This  is  learned  from  a  study  of  the  pro- 
ducts that  are  attracted  to  the  anode  and  cathode,  respectively,  in 
electrolysis,  and  from  the  manner  in  which  molecules  of  electrolytes 
exchange  their  parts  or  radicals  in  chemical  actions.  In  molecules 


THEORY  OF  ELECTROLYTIC  DISSOCIATION,   ETC.  191 

of  acids  hydrogen  is  readily  separated  in  chemical  actions  from  the 
rest  of  the  molecule,  which  is  a  radical,  consisting  of  a  non-metallic 
element,  or  a  group  of  atoms  acting  as  a  unit  and  remaining  intact. 
In  electrolysis,  division  occurs  in  the  same  manner,  hydrogen  sepa- 
rating at  the  cathode,  and  acid  radical  being  attracted  to  the  anode. 
Salts  behave  in  the  same  manner  as  acids  in  regard  to  the  division 
of  the  molecules,  which  is  only  what  we  should  expect,  since  they 
are  so  closely  related  to  acids.  Indeed,  some  chemists  put  both  in 
the  same  class,  regarding  acids  as  salts  of  hydrogen.  Bases  in  chemical 
action  and  in  electrolysis  show  a  division  between  the  metal  and 
the  hydroxyl  (OH)  radical,  the  metal  going  to  the  cathode,  and  the 
hydroxyl  radical  to  the  anode.  It  appears,  then,  from  the  side  of 
chemical  action  as  well  as  that  of  electrolysis  that  an  aqueous  solution 
of  an  acid  contains  positive  hydrogen  ions  and  negative  acid  radical 
ions;  a  solution  of  a  salt  contains  positive  ions  of  a  metal  and  negative 
acid  radical  ions;  and  a  solution  of  a  base  contains  positive  ions  of  a 
metal  and  negative  hydroxyl  ions. 

Ions  and  atoms  not  the  same.  The  student  should  note  partic- 
ularly that  a  substance  in  the  ionic  state  is  quite  different  from  the 
substance  in  the  free  state.  Simple  ions  are  atoms  plus  a  charge  of 
electricity,  while  atoms  of  free  elements  are  not  charged,  and  this 
difference  is  sufficient  to  account  for  the  difference  of  behavior. 
Thus,  when  sodium  chloride  (NaCl)  is  dissolved  in  water,  many  of 
the  molecules  break  up  into  Na-ions  and  Cl-ions,  but  there  is  tio 
chemical  action  between  the  water  and  Na-ions  or  Cl-ions,  whereas 
sodium  in  the  free  state  acts  violently  on  water,  and  chlorine  dissolves 
in  water  with  some  chemical  action  and  imparts  its  odor  and  bleach- 
ing properties  to  the  water.  A  solution  of  sodium  chloride  has  no 
odor  or  bleaching  action. 

Symbols  representing-  ions.  Ions  are  represented  by  the  usual 
chemical  symbols,  with  the  addition  of  marks  to  indicate  positive  and 
negative  charges.  Thus,  Na+,  or  Na',  stands  for  a  positively  charged 
sodium  ion,  and  Cl~,  or  Cl',  stands  for  a  negatively  charged  ion  of 
chlorine.  Quantitative  experiments  in  electrolysis  show  that  the 
amounts  of  electricity  possessed  by  ions  is  proportional  to  the  valence 
of  the  atoms  or  radicals  constituting  the  ions.  If  the  charge  on  a 
sodium  or  on  a  chlorine  ion  is  taken  as  the  unit  charge,  then  the 
charge  on  an  ion  of  a  bivalent  atom  or  radical  is  two  units,  and  is 
represented  thus,  Ca++,  or  Ca",  and  SO7~,  or  SO/'.  The  ion  of 
trivalent  aluminum  is  written  Al+++,  or  Al" ',  etc. 


192  NON-METALS  AND   THEIR   COMBINATIONS. 

Ionic  equilibrium.  The  dissociation  of  molecules  into  ions  must 
be  considered  as  a  species  of  chemical  change,  and,  like  many  others, 
it  is  a  reversible  action  (see  page  114).  In  ordinary  dilute  solutions 
there  is  always  a  certain  proportion  of  undissociated  molecules  which 
are  in  equilibrium  with  the  ions.  The  degree  of  dissociation  varies 
with  the  concentration  of  the  solution,  and  of  course  with  the  nature 
of  the  dissolved  substance,  since  for  the  same  concentration  different 
substances  vary  widely  in  the  amount  of  dissociation.  If  the  solution 
is  made  more  concentrated,  as  by  evaporation,  more  and  more  of  the 
ions  unite  to  form  molecules,  until  finally,  when  all  the  solvent  is 
removed,  the  dry  substance  is  left  entirely  in  the  molecular  state.  On 
the  other  hand,  diluting  a  solution  results  in  more  molecules  being 
dissociated.  Many  substances  in  highly  diluted  solutions  are  almost 
completely  dissociated.  The  reversible  character  of  dissociation  is 
represented  by  reversible  ionic  equations  thus  : 

HC1  ^  H-  -f  Cl' ;   NaCl  ;±  Na'  +  Cl' ;   NaOH  ;±  Na'  -f  (OH)'. 

The  first  equation  means  that  in  any  given  solution  of  hydrochloric 
acid  there  is  a  certain  proportion  of  molecules  and  a  certain  propor- 
tion of  ions.  The  molecules  tend  to  form  ions,  but  only  as  fast  as 
the  ions  tend  to  revert  to  the  molecular  state,  so  that  an  equilibrium 
is  maintained.  By  changing  the  conditions,  ions  may  be  forced  to 
unite  to  form  molecules,  or  vice  versa.  In  other  words,  the  equilib- 
rium may  be  displaced  forward  or  backward.  Likewise  for  the  other 
two  equations  dealing  with  sodium  chloride  and  sodium  hydroxide 
respectively. 

Theoretical  deductions,  as  well  as  experimental  results,  show  that 
in  varying  solutions  of  the  same  substance  there  is  a  constant  rela- 
tionship, which  is  expressed  thus  :  The  product  of  the  concentration  of 
the  ions  divided  by  the  concentration  of  the  undissociated  molecules  is  a 
constant  quantity  (or  nearly  so  in  some  cases),  expressed  by  a  numeral, 
and  called  the  IONIZATION  CONSTANT.  The  concentration  is  ex- 
pressed in  terms  of  the  number  of  molecular  weights  or  ion  weights 
in  grammes  in  a  liter  of  solution.  A  solution  containing  one  molec- 
ular weight  or  ion  weight  per  liter  is  taken  as  unit  concentration. 

Effect  of  ionic  equilibrium  in  chemical  reactions.  Some  fa- 
miliar results.  If  in  any  manner,  as  by  precipitation,  one  kind  of 
the  ions  of  a  substance  is  removed  from  solution,  some  molecules  of 
the  substance  are  dissociated  to  replace  the  kind  of  ions  removed, 
until  the  balance  between  ions  and  molecules,  as  indicated  in  the 
lonization  constant,  is  restored.  This  process  may  go  on  until  all  the 


THEORY  OF  ELECTROLYTIC  DISSOCIATION,   ETC.  193 

molecules  are  dissociated.  Conversely,  if  the  concentration  of  one 
kind  of  ion  is  increased,  as  by  the  addition  of  a  substance  giving  the 
same  kind  of  ion — for  example,  addition  of  hydrochloric  acid  to  a 

solution  of  sodium  chloride  (both  having  a  common  ion,  Cl') the 

result  is  a  reunion  of  some  of  the  ions  of  the  original  substance  to 
form  molecules,  until  the  balance  between  its  molecules  and  all  of  the 
ions  of  the  kinds  that  it  gives  satisfies  the  demands  of  the  ionization 
constant.  If  the  solution  is  saturated  in  the  beginning,  and  there- 
fore contains  all  the  undissociated  molecules  that  it  can  hold,  the  for- 
mation of  an  additional  number  of  molecules  by  union  of  ions  gives 
rise  to  supersaturation  and  precipitation  of  some  of  the  substance. 
Thus,  the  addition  of  hydrochloric  acid  gas  to  a  saturated  solution  of 
common  salt  causes  a  copious  precipitate  of  the  salt.  Likewise,  addi- 
tion of  some  saturated  solution  of  the  very  soluble  sodium  chlorate 
to  one  of  the  less  soluble  potassium  chlorate  causes  precipitation  of 
some  of  the  latter  salt.  The  reason  the  sodium  chlorate  is  not  also 
reciprocally  precipitated  is  that  the  additional  molecules  formed  by 
union  of  its  ions,  Na"  and  CIO/,  are  not  sufficient  to  supersaturate  the 
volume  of  liquid  through  which  the  sodium  chlorate  is  distributed. 
The  principle  just  discussed  furnishes  an  explanation  of  the  fact  that 
is  often  observed  in  practical  work ;  namely,  that  many  substances 
are  much  less  soluble  in  solutions  of  other  substances  of  similar  com- 
position than  in  pure  water. 

In  the  case  of  a  solution  of  a  slightly  dissociating  substance,  the 
addition  of  another  substance  having  a  common  ion  with  the  first 
may  so  far  cause  a  reversal  of  dissociation  of  the  first  substance  that 
practically  only  its  undissociated  molecules  exist  in  the  solution,  with 
an  accompanying  loss  of  some  of  its  properties.  Thus,  in  a  solution 
containing  per  liter  the  molecular  weight  of  sodium  acetate  and  the 
molecular  weight  of  acetic  acid,  the  latter  no  longer  is  able  to  affect 
the  indicator  methyl-orange,  because  there  are  too  few  hydrogen  ions 
of  the  acid  left  in  solution. 

Precipitation.  When  molecules  of  a  substance  are  dissolved,  some 
dissociate  until  a  balance  is  established  between  ions  and  molecules,  as 
represented  by  the  ionization  constant.  Conversely,  when  there  are 
present  in  a  solution  two  substances  which  between  them  produce  ions 
corresponding  to  a  third  substance,  some  molecules  of  the  third  sub- 
stance are  formed  up  to  the  point  that  corresponds  to  its  ionization 
constant.  The  following  ionic  equations  for  a  mixture  of  potassium 
chloride  and  sodium  nitrate  in  solution  will  illustrate : 

13 


194  NON-METALS  AND   THEIR   COMBINATIONS. 

KC1       ^K-      +Cl'j       Xaa 
NaN03  ^  N0'3  +  Na-  J 

It 
KN03 

Evidently  molecules  of  four  products  will  be  present  in  this  mixture, 
and  likewise  in  all  similar  ones.  If  all  the  products  are  readily  solu- 
ble and  of  large  dissociating  power,  and  the  solution  is  rather  dilute, 
there  are  few  undissociated  molecules  present.  The  mixture  then  is 
practically  a  mixture  of  ions,  and  nothing  can  be  observed  by  the 
eye  to  have  taken  place.  But  if  one  of  the  new  products  is  "  insolu- 
ble" in  water,  there  are  more  of  its  ions  present  than  can  be  main- 
tained in  a  saturated  solution  of  the  same,  the  excess  of  ions  unite  to 
form  molecules,  and  the  excess  of  molecules  are  removed  by  precipi- 
tation. In  this  way  one  factor  in  the  equilibrium  is  removed  and  the 
action  runs  to  completion.  This  principle  is  at  the  basis  of  all  cases 
of  precipitation  in  chemical  reactions.  The  precipitation  of  silver 
chloride  is  a  good  example,  and  is  represented  thus : 


It 

NaN03  soluble. 

A  simple  equation,  in  which  only  the  ions  are  represented,  may  be 
used : 

Ag-  +  NOS'  +  Na-  +  Cl'  =  AgCl  4-  Na'  4-  NO3'. 

The  simplest  equation  of  all  is  one  which  shows  only  those  ions  that 
are  actually  involved  in  the  precipitation,  thus  : 

Ag-  4-  Cl'  =  AgCl. 

Reasoning  parallel  to  the  above  may  be  applied  when  one  of  the 
new  products  formed  is  a  gas  with  slight  solubility  in  water  at  ordi- 
nary or  higher  temperatures,  or  a  liquid  which  is  volatile  at  elevated 
temperature.  In  either  case,  the  new  product  is  removed  as  fast  as 
it  is  formed  and  the  action  runs  to  completion.  In  the  liberation  of 
ammonia,  the  ionic  equations  are  : 

2XH4C1  ^±  2C1'  4-  2NH4-    1  _ 

Ca(OH)2  ;±  Ca-  •  4-  2(OHV  /  *~  2^^*^H  =  2H2O  4-  2NH3  (gas)  undissociated. 

It. 
CaCl2  soluble. 

Or,  more  simply, 

Ca-  •  4-  2(OH)'  4-  2NH4-  4-  2C1'  ==  Ca'  •  +2C1'  4-  2NH4OH. 

Ammonium  hydroxide  is  only  slightly  ionized,  and  by  heating  is 
easily  broken  up  and  driven  out  of  solution  as  ammonia*gas. 


THEORY  OF  ELECTROLYTIC  DISSOCIATION,   ETC.          195 

For  the  liberation  of  carbon-dioxide  gas  the  representation  is  this  : 

Na2C03  ^±  2Na'  +  CO/  '  )  ^  „  rn        „ 

H2S04    ^S04"  +  2H-     /-H2C°3=H20  +  C02(gas). 

I  t 
Na2SO4  soluble. 

Or  simply 

2Na-  +  CO/  '  +  2H-  +  SO/  '  =  2Na'  +  SO/  '  +  H2CO3. 

Carbonic  acid  is  only  slightly  ionized  and  very  little  soluble.    Hence 
it  escapes  as  fast  as  it  is  liberated.     This  description  will  serve  also 
for  the  liberation  of  nitrous  acid  from  nitrites. 
The  formation  of  nitric  acid  is  represented  thus  : 


it 

K2SO4  non-volatile. 

Or  simply 

2K-  +  2NO3'  +  2H-  +  SO/'  =  2K-  +  SO/'  +  2HNO3. 

As  concentrated  sulphuric  acid  and  dry  potassium  nitrate  are  used  in 
this  process,  only  a  relatively  small  number  of  ions  are  present  at  one 
time,  but  as  fast  as  ions  are  removed  as  nitric  acid,  new  ions  are 
formed  to  replace  them  until  the  operation  is  completed. 

The  above  discussions  on  the  formation  of  precipitates,  gases,  and 
volatile  liquids,  and  consequent  completion  of  chemical  reactions,  is  a 
presentation  in  terms  of  the  ionic  theory  of  the  same  subjects  dis- 
cussed in  a  simpler  form  on  p.  114,  under  Reversible  Actions  and 
Chemical  Equilibrium,  and  furnish  an  explanation  of  what  is  there 
stated. 

Chemical  actions  in  aqueous  solutions  are  nearly  always  actions 
between  ions.  Indeed,  there  are  some  who  claim  that  chemical  action 
does  not  take  place  except  between  ions,  and  the  fact  that  action  does 
occur  is  itself  evidence  of  the  presence  of  ions.  This  is  an  extreme 
view  and  is  not  well  taken,  as  there  are  undoubted  examples  of  action 
in  solution  in  which  ions  do  not  exist.  In  the  case  of  acids,  bases, 
and  salts  in  solution,  action  is  practically  always  ionic. 

Electrolysis. 

This  name  is  given  to  the  series  of  changes  that  take  place  when  an  electric 
current  is  passed  through  a  solution  of  an  electrolyte,  and  the  subject  is  briefly 
discussed  on  page  82.  The  process  is  carried  out  in  an  electrolytic  cell,  which 
consists  of  a  suitable  vessel  holding  a  solution  into  which  are  immersed  the 
electrodes  of  the  circuit.  Fig.  34  illustrates  one  form  of  such  a  cell,  which 


]96  NON-METALS  AND    THEIR   COMBINATIONS. 

is  designed  to  collect  gases.  The  electrodes  are  made  of  materials  which  are 
not  affected  by  the  products  that  collect  on  them.  Platinum  plates  are  often 
used. 

The  result  of  passing  a  current  through  a  solution  of  an  electrolyte  is  a 
chemical  decomposition.  The  products  that  appear  at  the  electrodes  are  always 
different.  For  illustration,  one  of  the  simplest  cases  of  electrolysis  may  be 
considered,  namely,  the  decomposition  of  hydrochloric  acid.  When  the  appa- 
ratus (Fig.  34)  is  filled  with  the  concentrated  acid  and  a  current  is  turned  on, 
hydrogen  gas  is  found  to  collect  and  rise  into  the  tube  from  the  cathode  or 
( — )  electrode,  and  chlorine  gas  collects  in  the  other  tube  from  the  anode  or 
(+)  electrode.  The  mechanism  of  the  process  is  conceived  to  be  as  follows : 
The  solution  of  the  acid  contains  some  ions  of  hydrogen  (H')  and  of  chlorine 
(Cl'),  the  presence  of  which  is  entirely  independent  of  the  electric  current. 
These  ions,  before  the  current  is  turned  on,  are  attracted  no  more  in  one  direc- 
tion than  in  any  other.  When  the  current  is  turned  on,  one  electrode  receives 
from  the  battery  or  dynamo,  or  whatever  the  source  of  electricity,  a  positive 
charge,  and  the  other  receives  a  negative  charge,  and  a  constant  difference  of 
voltage  or  electromotive  force  is  maintained  between  the  electrodes.  If  the 
latter  should  be  connected  by  a  continuous  conductor,  as  a  piece  of  copper  wire, 
a  current  would  flow  from  the  positive  to  the  negative  electrode  by  their  dis- 
charge through  the  wire.  But  the  source  of  electricity  would  constantly  renew 
the  charges  on  the  electrodes,  and  thus  a  continuous  current  would  be  kept  up. 
When  the  connecting  wire  is  replaced  by  hydrochloric  acid,  the  positive  elec- 
trode attracts  the  negatively  charged  chlorine  ions  and  repels  the  positive 
hydrogen  ions,  while  the  negative  electrode  attracts  the  positive  hydrogen  ions 
and  repels  the  negative  chlorine  ions.  In  this  way  there  is  a  general  move- 
ment of  all  positive  ions  to  one  electrode,  and  of  all  negative  ions  to  the  other. 
When  the  ions  come  in  contact  with  the  electrodes,  they  lose  their  charges  by 
neutralizing  the  charges  of  opposite  kind  on  the  electrodes.  The  discharged 
ions  then  unite  and  pass  off  as  molecules  of  hydrogen  and  chlorine  respect- 
ively. The  discharged  electrodes  receive  new  charges  as  before,  and  the  pro- 
cess is  repeated  until  all  of  the  electrolyte  is  removed  from  the  solution.  The 
effect  as  far  as  the  conduction  of  the  current  is  concerned  is  the  same  as  if  a 
wire  connected  the  electrodes,  and  the  current  flowed  through  a  circuit  entirely 
metallic.  In  the  light  of  this  ionic  explanation  of  electrolysis,  we  can  under- 
stand why  solutions  of  substances  which  do  not  dissociate  into  ions  like  sujrar 
do  not  conduct  electricity,  and  why  substances  which  conduct  in  aqueous  solu- 
tion do  not  conduct  in  solvents  in  which  they  are  not  dissociated. 

Secondary  changes  in  electrolysis.    In  the  electrolysis  of  hydrochloric 

id  the  products  liberated  consist  of  the  same  elements  of  which  the  ions  are 

constituted,  but  the  majority  of  cases  are  not  so  simple  as  this  one.     Many  ions 

are  atomic  groups  which  are  not  known  in  the  free  state,  but  exist  only  as  ions 

solution.     When  these  lose  their  charges,  secondary  chemical  changes  occur 

the  resulting  products  accumulate  around  the  electrodes.     Thus  in  the 

case^of  sulphuric  acid,  the  H'  ions  become  molecules  of  hydrogen  gas,  but  the 

>04     ion  when  discharged  becomes  a  group  not  known  in  the  free  state      It 

reacts  with  water  thus  :  H2O  +  SO4  =  H2SO4  +  O.     Sulphuric  acid  accumu- 

ound  the  positive  electrode,  but  is  gradually  disseminated  again  through 


THEORY  OF  ELECTROLYTIC  DISSOCIATION,   ETC.          197 

the  solvent  by  diffusion.  The  oxygen  escapes  and  can  be  collected.  The 
amount  of  hydrogen  and  oxygen  liberated  are  in  the  same  proportion  as  in 
water,  and  thus  we  have  an  explanation  of  the  "  decomposition  of  water  by 
electrolysis." 

When  copper  sulphate  is  electrolyzed  metallic  copper  is  deposited  on  the 
negative  electrode,  and  sulphuric  acid  and  oxygen  collect  at  the  other.  In  the 
case  of  sodium  sulphate  the  sodium  ion  when  discharged  acts  on  water,  result- 
ing in  the  accumulation  of  sodium  hydroxide  and  hydrogen  around  the  nega- 
tive electrode,  and  as  before  sulphuric  acid  and  oxygen  collect  at  the  positive 
electrode. 

Faraday's  laws  of  electrolysis,  Michael  Faraday,  of  England,  was  the 
first  to  make  a  careful  quantitative  study  of  electrolysis,  and  announced  the 
following  two  laws: 

I.  The  amount  of  a  substance  liberated  in  an  electrolytic  cell  is  proportional  to 
the  quantity  of  electricity  that  has  passed  through  it. 

II.  Chemically  equivalent  quantities  of  ions  are  liberated  by  the  passage  of  equal 
quantities  of  electricity.     Chemically  equivalent  quantities  are  determined  by 
valence.     Thus  for  every  divalent  ion  liberated,  two  univalent  ions  are  liber- 
ated, etc.,  by  the  same  amount  of  electricity. 

The  liberation  of  1  gramme  of  hydrogen  requires  the  passage  of  96,540  units 
(coulombs)  of  electricity.  A  current  strength  of  1  ampere  is  such  that  1  cou- 
lomb of  electricity  flows  through  a  circuit  in  1  second.  Hence  a  current  of 
1  ampere  will  require  96,540  seconds  (26  hours  and  49  minutes)  to  liberate 
1  gramme  of  hydrogen  (nearly  11  liters).  A  current  of  5  amperes  would  do  the 
same  work  in  one-fifth  of  the  time. 

One  coulomb  (a  current  of  1  ampere  flowing  1  second)  will  liberate  0.0000104 
gramme  of  hydrogen,  0.0000828  gramme  of  oxygen,  0.0003294  gramme  of 
copper,  0.001118  gramme  of  silver,  etc.  These  quantities  are  proportional  to 
the  chemical  equivalents,  and  are  called  in  electrical  science,  electro-chemical 
equivalents. 

An  instrument  constructed  for  determining  the  amount  of  a  substance  as 
silver  or  copper  liberated  by  a  current  in  a  given  time,  and  from  this  the  cur- 
rent strength,  is  called  a  voltameter  (see  page  77).  Suppose  a  current  flowing 
for  1  hour  through  a  voltameter  liberates  0.59292  gramme  of  copper  upon  the 
cathode,  the  current  strength  is — 

0.59292  gm.  copper =  i         ^ 

3600  seconds  X  0.0003294  elect,  chem.  equiv.  of  copper 

Conductivity.  Every  solution  of  an  electrolyte  offers  a  certain  resistance 
to  the  flow  of  the  current,  which  can  be  measured  in  ohms  (see  page  76).  If 
the  resistance  is  small,  the  solution  offers  an  easy  passage  for  the  current,  hence 
it  is  said  to  have  a  high  conductivity.  A  solution  of  great  resistance  is  said  to 
have  a  low  conductivity.  The  numerical  value  for  conductivity  is  the  recip- 
rocal of  the  resistance,  thus: 

Conductivity  =  — 

resistance 

In  order  that  results  may  be  compared,  conductivity  measurements  are  made 
with  electrodes  1  cm.  apart.     The  algebraic  character  used  to  represent  con- 


198  NON-METALS  AND   THEIR  COMBINATIONS. 

ductivity  is  Av,  which  means  the  conductivity  shown  by  the  molecular  weight 
of  the  substance  in  v  liters  of  solution. 

The  conductivity  increases  with  dilution.  This  is  what  we  should  expect, 
since  conductivity  is  proportional  to  the  number  of  ions,  which  also  increases 
with  dilution.  By  measuring  the  conductivity  in  a  given  dilution  and  also  in 
very  large  dilution,  it  is  a  simple  matter  to  calculate  the  degree  of  ionization 
of  the  substance  in  the  given  dilution.  This  method  of  study  is  called  the 
conductivity  method. 

Electromotive  force  required  in  electrolysis.  The  amount  of  work 
that  can  be  done  by  any  form  of  energy  depends  not  merely  on  the  quantity, 
but  also  on  the  intensity  of  the  energy.  Thus,  the  quantity  of  steam  in  a  loco- 
motive boiler,  however  large,  will  not  cause  the  driving-wheels  to  turn  if  the 
pressure  (intensity  factor)  is  not  sufficiently  large.  Likewise,  in  electrolysis, 
different  substances  require  for  decomposition  currents  of  different  electro- 
motive force.  If  the  latter  is  less  than  the  required  minimum,  there  is  no 
liberation  of  ions  at  the  electrodes,  that  is,  no  electrolysis.  The  quantity  of 
current  only  controls  the  amount  of  material  liberated,  but  the  electromotive 
force  decides  whether  there  will  be  any  decomposition  at  all.  The  reason  for 
the  latter  fact  is  that  as  soon  as  the  electrodes  are  coated  with  the  products  of 
electrolysis,  a  reverse  electromotive  force  and  current  tend  to  develop  which 
oppose  the  original  current.  The  electrodes  are  then  said  to  be  polarized.  To 
overcome  this  polarization  current  requires  a  certain  minimum  electromotive 
force  in  the  electrolyzing  current.  The  electromotive  force  required  for  a  few 
common  electrolytes  are  as  follows : 

Hydriodic  acid 0.53  volts. 

Silver  nitrate 0.7(5      " 

Hydrochloric  acid 1.41      " 

Sulphuric  acid 1.92     " 

Zinc  sulphate  .    . 2.70     " 

Electrochemical  series  of  the  metals.  If  the  metals  are  arranged  in 
the  order  of  the  electromotive  force  required  to  liberate  them  in  electrolysis, 
we  have  the  following  electropositive  series  : 

Electrochemical  series  of  metals. 

Potassium  Gold 

Sodium  Platinum 

Lithium  Palladium 

Calcium  Silver 

Strontium  Mercury 

Barium  Bismuth 

Magnesium  Antimony 

Aluminum  Copper 

Manganese  Arsenic 

Zinc  Hydrogen 
Chromium                                                    Lead 
Cadmium                                          Tin 
Iron                              Nickel 
Cobalt 


THEORY  OF  ELECTROLYTIC  DISSOCIATION,   ETC.          199 

The  electromotive  force  required  decreases  from  the  potassium  end  of  the 
series  to  the  gold  end.  If  the  metals  are  arranged  in  a  series  according  to  the 
decreasing  intensity  of  their  chemical  activity  in  the  free  state  toward  other 
substances,  the  same  order  is  observed  as  that  in  the  above  series.  Metals 
higher  up  in  the  series  will  displace  others  following  from  solutions  of  their 
salts,  but  not  vice  versa.  All  the  metals,  from  potassium  to  hydrogen,  will 
displace  hydrogen  from  dilute  acids,  but  those  following  hydrogen  will  not. 
The  metals,  down  to  copper  inclusive,  will  rust  in  the  air.  The  oxides  of  the 
metals,  down  to  manganese  inclusive,  cannot  be  reduced  to  the  metal  by  heat- 
ing in  hydrogen,  but  oxides  of  cadmium  and  the  metals  following  can.  The 
metals  down  to  hydrogen  do  not  occur  in  the  free  state  in  nature. 

The  non-metals  and  negative  radicals  into  which  they  enter  (acid  radicals) 
can  also  be  arranged  into  a  similar  electronegative  series. 

Discociation  theory  applied  to  acids,  bases,  salts,  and  neutral- 
ization. 

Acids.  A  general  discussion  of  acids,  bases,  and  salts  is  given  in  Chapter 
8.  In  terms  of  the  ionic  theory,  acids  are  substances  which  give  positive  hy- 
drogen ions  in  solution,  associated  with  negative  ions  tbat  may  be  either 
simple,  as  OF,  or  complex,  as  SO/',  or  CO3//.  The  properties  common  to  all 
acids  are  due  to  the  hydrogen  ions ;  for  example,  sour  taste,  action  on  litmus, 
action  on  metals  with  displacement  of  the  hydrogen.  The  latter  action  is  rep- 
resented in  the  case  of  zinc  by  the  ionic  equation,  Zn  +  2ET  -|-  SO/'  =  Zn**  4- 
SO4"  +  H2.  This  stands  as  a  type  for  all  acids,  and  it  will  be  observed  that 
the  action  is  essentially  between  the  metal  and  hydrogen  ions,  and  is  independ- 
ent of  the  negative  ion.  The  charges  on  the  hydrogen  ions  are  transferred  to 
the  zinc  atoms,  which  then  become  ionic,  and  the  discharged  hydrogen  ions 
escape  as  molecules. 

The  specific  properties  of  the  acids  in  solution  are  due  to  the  different  com- 
position of  the  negative  radicals.  These  radicals  are  the  same  whether  acids 
or  their  salts  are  used.  When  a  solution  of  silver  nitrate  is  added  to  one  of 
potassium  chloride,  a  white  precipitate  of  silver  chloride  is  obtained,  but  when 
added  to  potassium  chlorate  in  solution,  no  visible  change  takes  place.  Both 
of  these  salts  contain  chlorine,  but  the  first  gives  the  ion  CK,  and  the  second 
the  ion  CIO/.  In  other  words,  the  composition  of  the  negative  radicals  is 
different,  which  results  in  a  different  behavior  toward  the  positive  silver  ion. 
Silver  chloride  is  an  insoluble  substance  and  is  formed  in  solutions  only  when 
silver  ions  and  chlorine  ions  are  brought  together.  Chlorine  ions  are  formed 
only  from  hydrochloric  acid  or  the  chlorides.  Silver  chlorate  is  a  soluble 
body,  and,  therefore,  nothing  that  we  can  see  happens  when  silver  ions  and 
chlorate  ions  are  brought  together  in  solution. 

Independence  of  ions.  The  above  discussion  leads  to  the  conclusion 
that  the  ions  of  acids  are  distinct  substances  with  individual  physical  and 
chemical  properties.  Each  kind  of  ion  behaves  as  if  it  were  alone  present  in 
the  solution.  This  is  true  of  all  ions.  To  illustrate,  two  instances  may  be 
given  that  have  to  do  with  a  physical  property,  namely,  color  of  salts  or  acids. 
All  copper  salts  of  colorless  acids  have  a  blue  color  in  dilute  solutions.  The 
blue  color  is  due  to  the  copper  ion,  and  all  copper  salts  that  are  soluble  give 


200  NON-METALS  AND  THEIR  COMBINATIONS. 

the  copper  ion.  The  molecules  of  copper  salts  in  solution  are  not  blue,  as  can 
be  shown  by  the  following  experiment:  If  to  a  solution  of  copper  chloride 
concentrated  hydrochloric  acid  be  added,  there  will  be  a  point  at  which  the 
blue  changes  to  a  yellowish-green  color.  The  effect  of  the  acid  is  to  reverse 
the  ionization  of  the  copper  chloride  so  far  that  the  color  of  the  remaining 
ions  of  copper  is  overbalanced  by  the  color  of  the  molecules  of  the  salt. 

Again,  permanganic  acid  in  dilute  solution  is  deeply  colored,  due  to  the 
MnO/  ion  (hydrogen  ion  is  colorless).  Likewise  all  its  salts  in  dilute  solu- 
tions are  deeply  colored,  because  they  all  form  the  common  ion,  MnO/.  For 
equivalent  concentrations,  the  tint  of  the  color  is  the  same  in  all  the  solutions. 

Analytical  reactions  or  tests.  Since  acids,  bases,  and  salts  ionize,  and 
chemical  actions  concern  primarily  the  ions,  it  is  not  difficult  to  see  that  the 
tests  made  in  solutions  (wet  way)  for  identifying  substances  are  tests  for  ions. 
Thus,  when  we  test  for  carbonic  acid  by  lime-water  we  are  testing,  not  for  the 
acid  H2CO3,  but  for  the  ion  CO/'.  Nevertheless  we  infer  the  nature  of  the 
molecules  from  a  study  of  the  reactions  of  the  ions.  Since  the  tests  apply  to 
ions,  we  have  an  explanation  of  the  fact  that  tests  for  a  given  ion  can  be  used 
in  the  case  of  all  substances  which  give  that  ion  in  solution,  irrespective  of  the 
nature  of  the  other  ions.  Thus,  the  silver  nitrate  test  for  "  chlorine  "  succeeds 
for  all  chlorides  that  are  soluble.  Likewise,  the  barium  chloride  test  for  all 
soluble  sulphates.  It  is  evident  also  that  two  kinds  of  tests  must  be  made  in 
the  case  of  each  substance,  namely,  one  kind  for  the  positive  ion  and  the  other 
kind  for  the  negative  ion. 

Kinds  of  ions  formed  by  acids.  Monobasic  acids,  as  HC1,  HNO3,  etc., 
can  form  only  one  hydrogen  ion  from  each  molecule.  Dibasic  acids,  like 
H2SO4,  form  one  or  two  hydrogen  ions,  according  to  concentration.  In  rather 
concentrated  solution  of  sulphuric  acid  the  ionization  is  principally  thus: 
H2SO4  :±  H-  +  HSO/.  The  ion  HSO/  is  an  acid,  but  much  less  active  than 
sulphuric.  When  the  acid  is  highly  diluted,  further  ionization  takes  place  to 
a  great  degree,  thus,  HSO/  ^±  H*  -f  SO/'.  All  dibasic  acids  dissociate  in 
two  stages,  like  sulphuric.  Tribasic  acids  show  a  similar  behavior. 

Activity  or  "strength"  of  acids.  A  proper  comparison  of  acids  can 
only  be  made  under  like  conditions  of  temperature,  concentration,  etc.  For 
this  purpose  like  concentration  means  solutions  containing  in  a  given  volume 
chemically  equivalent  weights  of  the  respective  acids.  These  are  such  weights 
in  grammes  as  contain  the  same  weight  of  replaceable  hydrogen.  For  ex- 
ample, two  molecular  weights  of  HC1  are  equivalent  to  one  moleculer  weight 
of  H2SO4.  All  conditions  being  equal,  the  activity  of  acids  is  proportional  to 
the  degree  of  dissociation  ;  that  is,  to  the  concentration  of  the  hydrogen  ions. 
Those  acids  that  ionize  most  are  the  "strongest,"  and  vice  versa. 

Bases.  Bases  are  substances  which  give  negative  hydroxyl  (OH)  ions  in 
solution,  associated  with  a  positive  ion,  which  is  usually  metallic,  but  may  be 
a  group  of  atoms  not  containing  a  metal,  as  NH4.  The  properties  common  to 
bases  in  general  when  dissolved  are  due  to  the  hydroxyl  ion,  for  example, 
action  on  litmus,  soapy  taste,  neutralization  of  acids.  Most  of  the  bases  are 
so  sparingly  soluble  that  not  enough  (OH)  ions  are  present  to  affect  litmus. 
Zinc  and  iron  hydroxides  are  examples  of  such.  In  other  cases,  just  enough 


THEORY  OF  ELECTROLYTIC  DISSOCIATION,   ETC,          201 

(OH)  ions  dissolve  to  give  a  faint  action  on  litmus,  for  example,  magnesium 
hydroxide.  Just  as  in  the  case  of  acids,  the  activity  of  bases  is  proportional 
to  the  degree  of  ionization.  The  most  active  common  bases  are  potassium 
and  sodium  hydroxides,  called  alkalies,  and  sometimes  caustic  alkalies.  Their 
solutions  are  called  lyes.  The  hydroxides  of  barium,  strontium,  and  calcium 
are  next  in  activity.  Ammonium  hydroxide  is  a  rather  weak  base.  The  rest 
are  either  sparingly  soluble  or  insoluble. 

Salts.  The  relationship  between  salts  and  acids  has  already  been  discussed. 
As  a  rule,  salts  ionize  to  a  considerable  degree,  and  do  not  show  as  wide  a  range  in 
the  degree  as  do  the  acids.  Non-metals  are  never  found  in  the  positive  ion  of  salts, 
except  they  occur  in  a  composite  radical,  as  NH4.  Hence  we  have  no  such  salts 
as  nitrogen  carbonate,  carbon  sulphate,  or  sulphur  phosphate.  The  ions  of  salts 
do  not  affect  litmus,  it  is  only  H'  and  (OH)7  ions  that  have  an  effect. 

Acid  salts.  These  may  be  acid,  neutral,  or  alkaline  to  litmus,  depending 
on  the  mode  of  ionization.  An  acid  salt  of  a  highly  ionizing  acid  shows  an 
acid  reaction  in  solution,  because  of  the  presence  of  hydrogen  ions.  For  ex- 
ample, sodium  bisulphate  acts  thus  in  solution  : 

NaHSO4  ±?  Na'      +     HSO/ 
HSO/      ±?H-       4-     SO/ 

Acid  salts  of  weak  acids,  like  carbonic,  phosphoric,  boric,  etc.,  may  be  neutral 
or  even  alkaline,  because  the  remaining  hydrogen  of  the  acid  does  not  become 
ionic.  Sodium  bicarbonate  is  neutral  to  litmus,  because  it  ionizes  thus  : 

NaHCO3^±  Na-      +     HCO3'. 

The  ion  HCO/  does  not  furnish  sufficient  H'  ions  by  further  dissociation  to 
affect  litmus. 

Basic  salts,  These  are  the  reverse  of  acid  salts.  They  are  derived  from 
bases  containing  more  than  one  (OH)  group  in  the  molecule,  and  the  union 
with  acids  is  such  that  not  all  of  the  (OH)  groups  are  replaced  by  acid  radical. 

/Cl 

Thus  Mg  (OH)2  can  form  Mg<f  QTT  which  shows  the  plan  of  structure  of  all 

basic  salts.  They  are,  in  nearly  all  cases,  insoluble  in  water  and  show  slight  or 
no  action  on  litmus. 

Hydrolysis  of  salts.  Some  salts,  which  we  would  expect  from  their  for- 
mulas, such  as  normal  salts,  to  have  a  neutral  reaction  in  solution,  show  a 
noticeable  acid  reaction,  while  others  show  an  alkaline  one.  Such  salts  are 
related  to  an  acid  or  to  a  base  of  slight  dissociating  power,  and  the  cause  is 
found  in  the  slight  ionization  of  water,  which,  though  extremely  minute, 
makes  itself  felt  in  some  cases.  The  acid  reaction  of  copper  sulphate  is  ex- 
plained by  the  following  ionic  reaction  : 


2H20  :±2H'  +  2(OH)' 
Copper  hydroxide  dissociates  very  slightly,  being  in  this  respect  on  a  par 
with  water.  As  a  consequence,  some  Cu"  and  (OH)'  ions  unite  to  form 
molecules  of  Cu(OH)2.  The  removal  of  (OH)'  ions  of  water  allows  more  to 
be  formed,  and  more  Cu(OH)2  results.  This  process  soon  comes  to  a  stop,  but 
not  before  enough  H'  ions  have  been  produced  to  give  the  solution  an  acid  re- 
action. The  molecules  of  Cu(OH)2  are  not  precipitated,  but  remain  in  solu- 
tion. The  quantity  is  too  small. 


202  NON-METALS  AND  THEIR  COMBINATIONS. 

The  ionic  equation  for  sodium  carbonate  which  shows  marked  alkaline  reac- 

Na2C03  ;±  2Na'  +  CO/  1    _^  HCQ  , 
H20  ;±   (OH)'  +  H;    .  /."* 

Here  a  small  quantity  of  (OH)7  ions  are  produced,  which  give  the  solution  an 
alkaline  reaction.  This  action  of  water  on  salts  is  called  hydrolysis.  The 
changes  are  usually  represented  by  the  simpler  reactions : 

CuS04  +  2H20  =  Cu(OH),  +  H2S04 
Na2C03  +  H20  =  NaOH    +    NaHCO. 

Soap  always  shows  an  alkaline  reaction,  which  is  due  to  hydrolysis.  Salts 
containing  bivalent  or  trivalent  radicals,  metallic  or  acid,  are  more  prone  to 
undergo  hydrolysis  than  those  containing  univalent  radicals  only. 

Neutralization.  Broadly  speaking,  the  replacement  of  hydrogen  of  an  acid 
by  metal  is  neutralization,  but,  as  shown  in  the  preceding  paragraph,  certain 
salts  have  an  acid  or  alkaline  reaction  in  solution,  and  consequently  it  is 
impossible  in  such  instances  to  produce  an  exactly  neutral  solution  by  bring- 
ing the  acid  and  base  together  in  the  proportions  to  form  the  salt.  A  great 
many  salts,  however,  are  neutral,  and  in  these  cases  it  is  possible  to  bring 
together  the  corresponding  acids  and  bases,  and  have  complete  reactions  and 
neutral  solutions.  In  the  more  restricted  sense  neutralization  refers  to  such 
complete  reactions.  They  can  be  employed  for  quantitative  determinations 
of  the  acids  or  bases  in  solutions.  This  subject  is  treated  under  Acidimetry 
and  Alkalimetry  in  the  section  on  Volumetric  Analysis. 

Neutralization  is  an  example  of  double  decomposition  and  of  a  complete 
reaction.  The  interpretation  of  this  is  found  in  the  ionic  theory.  In  the 
beginning  before  mixing,  there  are  H*  ions  which  have  an  acid  reaction,  and 
(OH)'  ions  which  are  alkaline.  When  they  are  brought  together  by  mixing 
the  acid  and  base  and  the  neutral  point  is  established,  both  H*  and  (OH)'  ions 
disappear,  as  is  proved  experimentally  by  conductivity  tests.  This  disappear- 
ance results  from  the  fact  that  water  is  practically  undissociated.  and,  there- 
fore, these  ions  cannot  exist  in  the  same  solution,  but  unite  to  form  molecules 
of  water.  Of  course,  the  metal  ions  and  acid  radical  ions  also  unite  to  some 
extent  to  form  molecules,  but  if  the  solutions  are  quite  dilute  the  proportion 
of  undissociated  molecules  is  negligible. 

The  ionic  equation  for  the  neutralization  of  sodium  hydroxide  and  nitric 
acid  serves  as  a  type  for  all  instances : 

NaOH  ^  Na'  +  (OH)') 
HN03  ;±  NO./  +  H-        /  " 

It' 
NaNO3 

As  fast  as  H'  and  (OH)'  unite  more.  NaOH  and  HNO3  dissociate,  until  finally 
all  is  dissociated,  and  only  ions  of  sodium  nitrate  and  some  undissociated  mole- 
cules of  the  same  are  left  in  the  solution  at  the  point  of  neutrality. 
The  essential  reaction  may  be  shown  in  the  simplified  equation : 

Na-  +  (OH)'  +  H-  +  N03'  =  Na'  +  NO3'  -f  H2O, 

or  by  the  following  still  simpler  equation,  which  expresses  the  fact  that  neu- 
tralization is  a  reaction  between  H-  and  (OH)'  ions : 


THEORY  OF  ELECTROLYTIC  DISSOCIATION,   ETC.          203 

Heat  of  neutralization.  Heat  is  produced  when  an  acid  and  a  base  neu- 
tralize each  other.  If  what  is  stated  above  is  true,  then  the  heat  is  due  to  the 
formation  of  water  molecules,  and  should  be  the  same  for  all  active  acids  and 
bases  in  dilute  solutions.  This  is  exactly  what  is  found  by  experiment  to  be 
true.  The  heat  of  neutralization  refers  to  such  weights  of  acids  and  bases  that 
will  furnish  enough  H*  and  (OH)X  ions  to  form  one  molecular  weight  (17.88 
gin.)  of  water,  and  is  nearly  13,600  calories. 

Degree  of  dissociation.  The  degree  of  dissociation  of  electrolytes  varies 
with  the  nature  of  the  substance  and  the  concentration  of  the  solution.  Usu- 
ally it  is  small  in  concentrated  solutions,  and  increases  rapidly  with  dilution. 
In  62  per  cent,  nitric  acid  only  about  9  per  cent,  of  the  molecules  are  ionized, 
while  in  the  6.3  per  cent,  acid  about  80  per  cent,  are  ionized.  Comparisons 
for  degree  of  dissociation  must  be  made  with  solutions  of  the  same  relative  con- 
centrations. Usually  normal  solutions  at  18°  C.  are  used,  except  when  the 
substance  is  not  sufficiently  soluble.  The  following  table  gives  the  per  cent. 
of  dissociation  in  normal  solutions1  at  18°  C.,  except  when  otherwise  specified, 
of  some  acids,  bases,  and  salts. 

PerCent' 


Electrolyte.  ..  Electrolyte.  /, 

dissociation.  dissociation. 

Nitric  acid  ...........  82  Sodium  phosphate,  very  dilute  .    .  83 

Hydrochloric   acid    .......  78.4  Ammonium  chloride    ......  74 

Sulphuric  acid   .........  51  Sodium  chloride  ........  67.5 

Hydrofluoric  acid  ......        .7  Potassium  nitrate  ........  64 

Acetic  acid  ......    .....    0.4  Potassium  acetate  ........  64 

Carbonic  acid  (^)    .......    0.17  Silver  nitrate  .   .    . 

,n^  Potassium  sulphate  .......  53 

Hydrogen  sulphide  (jg)  .....    0.07  godium  acetate  .........  53 

Boric  acid  (^\  .........    0.01       Sodium  bicarbonate  .......  52 

.  ,  /  n  \  A  A1       Potassium  carbonate  ,   ......  49 

Hydrocyanic  acid  (1?))    .....    0.01 

Sodium  sulphate  ........  44.5 

Phosphoric  acid  (~  at  25°  C.)  .    .    .17  Zinc  sulphate  ..........  24 

Potassium  hydroxide  ......  77  Zinc  chloride  ..........  48 

Sodium  hydroxide    .......  73  Copper  sulphate    ........  22 

Calcium  hydroxide,  sat.  sol.  at  25°  C.  90  Mercuric  chloride,  less  than    ...    1 

Ammonium  hydroxide  ......    0.4         Mercuric  cyanide  .......  minute 

Mathematical  formulas  have  been  constructed  for  calculating  the  degree 
of  dissociation  from  the  results  obtained  by  four  methods  of  work,  namely, 
freezing-point,  boiling-point,  osmotic  pressure,  and  conductivity  methods. 
The  results  of  calculation  all  agree.  The  simplest  method  in  execution  is  the 
conductivity  method. 

QUESTIONS.—  State  the  theory  of  electrolytic  dissociation  or  ionization. 
Upon  what  experimental  facts  does  it  rest?  What  is  an  electrolyte?  What 
substances  are  found  to  be  electrolytes  ?  What  is  a  cation  ;  an  anion  ?  Write 
the  ionic  equation  for  the  dissociation  of  sodium  chloride  in  solution.  Write 
the  ionic  equation  for  the  precipitation  of  silver  chloride  from  solution.  What 
is  electrolysis,  and  how  is  it  explained?  How  are  acids,  bases,  and  salts  defined 
in  terms  of  the  ionic  theory  ?  How  is  the  activity  or  "  strength  "  of  acids  and  bases 
related  to  dissociation  ?  How  is  the  fact  that  some  acid  salts  have  an  acid  action 
on  litmus,  while  others  are  neutral,  accounted  for.?  What  is  hydrolysis? 
1  The  concentration  of  normal  solutions  is  denned  in  the  section  on  Volumetric  Analysis. 


204  NON-METALS  AND   THEIR   COMBINATIONS. 

16.   SULPHUR. 
S"  =  32  (31.83). 

Occurrence  in  nature.  Sulphur  is  found  in  the  uncombined 
state,  mixed  with  earthy  matter,  in  volcanic  districts,  the  chief  sup- 
ply having  been  derived  until  lately  from  Sicily.  Considerable 
quantities  are  now  also  mined  in  the  United  States,  chiefly  in  Louis- 
iana, Utah,  California,  and  Nevada.  In  combination  sulphur  is  widely 
diffused  in  the  form  of  sulphates  (gypsum,  CaSO4.2H2O),  and  fre- 
quently occurs  as  sulphides  (iron  pyrites,  FeS2,  galena,  PbS,  cinnabar, 
HgS,  etc.).  Sulphur  enters  also  into  organic  compounds,  being  a 
normal  constituent  of  all  proteids,  during  the  decomposition  of  which 
sulphur  is  often  evolved  as  hydrogen  sulphide,  which  gas  is  also  a 
constituent  of  some  waters. 

Properties.  Sulphur  is  a,  yellow,  brittle,  solid  substance,  having 
neither  taste  nor  odor.  It  is  insoluble  in  water  and  nearly  so  in 
alcohol ;  soluble  in  benzene,  benzin,  ether,  chloroform,  carbon  di- 
sulphide,  oil  of  turpentine,  and  fat  oils.  Sulphur  is  polymorphous  ; 
it  crystallizes,  from  a  solution  in  disnlphide  of  carbon,  in  octahedrons 
with  a  rhombic  base ;  when,  however,  liquefied  by  heat  it  crystallizes 
in  six-sided  prisms,  and  is  obtained  as  a  brown,  amorphous  plastic 
substance  by  pouring  melted  sulphur  into  cold  water. 

Sulphur  melts  at  115°  C.  (239°  F.)  to  an  amber-colored  liquid, 
which  is  fluid  as  water ;  increasing  the  heat  gradually,  it  becomes 
brown  and  thick,  and  at  about  200°  C.  (392°  F.)  it  is  so  tenacious 
that  it  scarcely  flows  ;  when  heated  still  further  it  again  becomes 
thin  and  liquid,  and,  finally,  boils  at  a  temperature  of  about  440°  C. 
(824°  F.). 

In  its  chemical  properties  sulphur  resembles  oxygen,  being  like 
this  element  generally  bivalent,  and  supporting,  when  in  the  form 
of  vapor,  the  combustion  of  many  substances,  especially  the  metals. 
Many  compounds  of  oxygen  and  sulphur  show  an  analogous  compo- 
sition, as,  for  instance,  H2O  and  H2S,  CO2  and  CS2,  CuO  and  CuS. 
While  the  valence  of  sulphur  as  a  general  rule  is  2,  in  some  com- 
pounds it  shows  a  valence  of  4  or  6,  as  in  SO2  and  SO3. 

Crude  sulphur  is  obtained  by  heating  the  rock  containing  sul- 
phur sufficiently  high  to  cause  the  sulphur  to  melt,  and  thus  to 
separate  from  the  earthy  matters.  As  peculiar  conditions  (great  depth 
and  quicksand)  prevented  successful  working  of  the  sulphur  deposits 
m  Louisiana  by  the  ordinary  methods,  sulphur  is  now  mined  there  by 
the  following  ingenious  process  :  Superheated  water,  forced  through 
iron  pipes  to  the  deposits  of  sulphur,  causes  the  latter  to  melt,  and  this 


SULPHUR.  205 

liquefied  sulphur  is  raised  through  other  pipes  to  the  surface  by  means 
of  compressed  air.  Crude  sulphur  generally  contains  from  2  to  4  per 
cent,  of  earthy  impurities. 

Sublimed  sulphur,  Sulphur  sublimatum  (Flowers  of  sulphur). 
Obtained  by  heating  sulphur  to  the  boiling-point  in  suitable  vessels, 
and  passing  the  vapor  into  large  chambers,  where  it  deposits  in  the 
form  of  a  powder,  composed  of  small  crystals.  Sublimed  sulphur, 
when  melted  and  poured  into  round  moulds,  is  known  as  roll-sulphur 
or  brimstone. 

"Washed  sulphur,  Sulphur  lotum,  is  sublimed  sulphur  washed 
with  a  very  dilute  ammonia  water,  and  then  with  pure  water ;  the 
object  of  this  treatment  being  to  free  the  sulphur  from  all  adhering 
sulphurous  and  sulphuric  acid,  as  also  from  arsenic  compounds  which 
are  sometimes  present. 

Precipitated  sulphur,  Sulphur  prsecipitatum  (Milk  of  sulphur). 
Made  by  boiling  one  part  of  calcium  hydroxide  with  two  parts  of 
sulphur  and  thirty  parts  of  water,  filtering  the  solution,  adding  to  it 
dilute  hydrochloric  acid  until  nearly  neutral,  washing  and  drying  the 
precipitated  sulphur. 

By  the  action  of  sulphur  on  calcium  hydroxide  are  formed  calcium  polysul- 
phide,  calcium  thiosulphate,  and  water: 

3Ca(OH)2     +     12S    :   :    2CaS5     +     CaS2O3     +     3H2O. 

On  adding  hydrochloric  acid  to  the  solution,  both  substances  are  decom- 
posed and  sulphur  is  liberated : 

2CaS5  +  CaS2O3  +  6HC1  =  3CaCl2  -f-  3H2O  +  12S. 

While  the  above  equation  gives  the  final  result,  the  decomposition  takes 
place  in  stages,  thus : 

CaS5  -f  2HC1    =  CaCl2  +  H2S  +  4S 
CaS2O3  +  2HC1     =  CaCl2  +  H2S2O8 
2H2S  +  H2S208  =  3H2O  +  4S. 

Precipitated  sulphur  differs  from  sublimed  sulphur  by  being  in  a  more  finely 
divided  state,  and  by  having  a  much  paler  yellow,  almost  white  color. 

Experiment  13.  Mix  in  a  beaker  about  10  grammes  of  powdered  sulphur,  20 
grammes  of  slaked  lime,  and  200  c.c.  of  water,  and  boil  until  the  liquid  has  a 
deep  brown  color.  Renew  the  water  that  is  lost  by  evaporation  occasionally. 
Note  that  the  color  deepens  as  boiling  is  continued.  This  is  due  to  the  poly- 
sulphide  of  calcium,  which  is  colored.  Finally,  filter  into  a  large  flask  or 
beaker,  wash  the  filter,  dilute  to  about  half  a  liter,  and  add  dilute  hydrochloric 
acid  until  the  solution  is  nearly  neutral.  Note  the  milk-like  appearance  of  the 
liquid.  Let  the  sulphur  settle  fully,  decant  the  liquid,  filter  and  wash  the  sulphur, 
and  let  it  dry  in  the  air.  Compare  its  appearance  with  that  of  lump  sulphur. 


206  NON-METALS  AND   THEIR   COMBINATIONS. 

The  following  four  oxides  are  known  :  Sulphur  sesquioxide,  S2O3 ; 
sulphur  dioxide,  SO2 ;  sulphur  trioxide,  SO3;  sulphur  heptoxide,  S2O7. 
The  three  last  named  are  acid  oxides,  which,  on  combining  with  one 
molecule  of  water,  form  sulphurous,  sulphuric,  and  persulphuric  acid 
respectively. 

Sulphur  dioxide,  SO2  =  63.59  (Sulphurous  anhydride,  improperly 
also  called  sulphurous  acid),  is  formed  when  sulphur  or  substances  con- 
taining it  in  a  combustible  form  (H2S,  CS2,  etc.)  burn  in  air.  It  is 
generated  also  by  the  action  of  strong  sulphuric  acid  on  many  metals 
(Cu,  Hg,  Ag,  etc.),  or  on  charcoal  : 

2H2SO4  +  Cu  =  CuSO4  +-2H2O  +  SO2. 
2H2SO4  +  C     =  CO2      +  2H2O  +  2SO2. 

Sulphur  dioxide  is  a  colorless  gas,  having  a  suffocating,  disagreeable 
odor;  it  liquefies  at  a  temperature  of — 10°  C.  (14°  F.),  and  solidifies 
at  — 75  C.  ( — 103°  F.) ;  it  is  very  soluble  in  water,  forming  sulphur- 
ous acid  ;  it  is  a  strong,  deoxidizing,  bleaching,  and  disinfecting 
agent ;  when  inhaled  in  a  pure  state  it  is  poisonous ;  when  diluted 
with  air  it  produces  coughing  and  irritation  of  the  air-passages. 

Sulphurous  acid,  Acidum  sulphurosum,  H2SO3,  SO2.H.OH.  This 
acid,  similar  to  carbonic  acid,  is  not  known  in  a  pure  state,  but  is 
believed  to  exist  in  aqueous  solution,  which  decomposes  into  water 
and  sulphur  dioxide  when  attempts  are  made  to  concentrate  it.  One 
volume  of  cold  water  absorbs  about  40  volumes  of  sulphur  dioxide, 
equal  to  about  11  per  cent,  by  weight.  The  official  acid  must  contain 
not  less  than  6  per  cent,  by  weight,  equal  to  about  2000  volumes  of 
gas  dissolved  in  100  of  water.  According  to  the  U.  S.  P.  the  acid 
is  made  by  generating  sulphur  dioxide  from  charcoal  and  sulphuric 
acid  in  a  flask,  and  passing  the  gas  through  a  wash-bottle  containing 
water,  inta  distilled  water  for  absorption. 

Experiment  14.  Use  an  apparatus  as  shown  in  Fig.  42.  Place  in  the  flask 
about  20  grammes  of  charcoal  in  small  pieces,  cover  it  with  sulphuric  acid, 
apply  heat,  and  pass  the  generated  gas  first  through  a  small  quantity  of  water 
contained  in  the  wash-bottle,  and  then  into  pure  water,  contained  in  the 
cylinder. 

The  solution,  sulphurous  acid,  may  be  used  for  the  tests  mentioned  below ; 
when  the  neutral  solution  of  a  sulphite  is  required,  make  this  by  adding  solu- 
tion of  sodium  carbonate  to  a  portion  of  the  sulphurous  acid  until  litmus-paper 
shows  neutral  reaction.  Examine  also  the  contents  of  the  wash-bottle  by 
means  of  the  tests  given  below  for  sulphuric  acid ;  most  likely  some  of  the 
latter  will  be  found.  How  much  carbon  and  how  much  H2S04  are  required  to 
make  100  grammes  of  a  6.4  per  cent,  sulphurous  acid? 


SULPHUR. 


207 


Sulphurous  acid  is  a  colorless  acid  liquid,  which  has  the  odor  as  well  as  the 
disinfecting  and  bleaching  properties  of  sulphur  dioxide;  it  is  completely 
volatilized  by  heat.  Sulphurous  acid  is  a  dibasic  acid,  the  salts  of  which  are 
termed  sulphites.  Both  the  acid  and  its  salts  are  easily  oxidized  by  the  air, 
and  hence  almost  always  give  the  tests  for  sulphuric  acid.  In  its  chemical  be- 
havior sulphurous  acid  is  very  much  like  carbonic  acid.  It  is  a  weak  acid, 
being  displaced  from  its  salts  by  all  acids  except  carbonic  and  boric.  The  sul- 
phites of  the  alkali  metals  are  freely  soluble  in  water,  but  the  normal  sulphites  of 
all  other  metals  are  insoluble  or  nearly  so ;  hence  addition  of  a  solution  of  an 
alkali  sulphite  to  a  solution  of  salts  of  the  other  metals  causes  precipitates.  A 

FIG.  42. 


Apparatus  for  making  sulphurous  acid. 

few  sulphites  are  soluble  in  a  solution  of  sulphurous  acid,  like  carbonates,  but 
are  precipitated  on  boiling.  Acid  sulphites  of  the  alkali  metals  can  be  obtained  in 
the  solid  state.  These  show  an  acid  reaction  to  litmus,  but  the  normal  sul- 
phites of  these  metals  have  an  alkaline  reaction,  due  to  hydrolysis  by  water 
into  bisulphite  and  free  alkali.  All  the  common  sulphites  are  white. 

The  ionic  equations  for  the  liberation  of  sulphurous  acid  from  a  sulphite, 
and  the  ionization  of  normal  and  bisulphites  in  solution,  are  ir  all  respects  like 
those  pertaining  to  the  liberation  of  carbonic  acid  and  the  ionization  of  normal 
and  bicarbonate  of  sodium,  which  are  given  on  pages  195  and  201.  The  reason 
that  bisulphites  are  slightly  acid  in  solution,  and  not  neutral  as  bicarbonates 
are,  is  that  an  appreciable  amount  of  hydrogen  ions  are  formed,  thus  : 


NaHSO3  ^ 


HS03' 
SO3". 


The  second  reaction  takes  place  only  to  a  small  degree. 


208  NON-METALS  AND   THEIR   COMBINATIONS. 

Tests  for  sulphurous  acid  and  sulphites. 
(Sodium  sulphite,  Na,SO3.7H2O,  may  be  used.) 

1.  Add  sulphur  dioxide  gas,  or  a  solution  of  it  in  water,  or  a  solu- 
tion of  a  sulphite  to  an  acidified  solution  of  potassium  permanganate. 
The  latter  is  decolorized,  due  to  its  giving  up  oxygen,  which  oxidizes 
the  sulphurous  acid,  thus  : 

H,S03    +    O  H2S04. 

Make  the  same  experiment  with  acidified  solution  of  potassium 
dichromate.  The  same  kind  of  change  takes  place,  but  the  decom- 
position products  of  the  dichromate  are  green.  The  reaction  will  be 
understood  when  chromium  is  studied. 

2.  Add  a  few  drops  of  a  solution  of  sulphurous  acid  or  of  a  sul- 
phite  to   a   tube    containing   some    zinc    and    dilute  sulphuric  acid 
(nascent  hydrogen).     Hydrogen  sulphide  is  liberated,  which  can  be 
detected  by  the  odor,  or  a  piece  of  filter-paper,  wet  with  solution  of 
lead  acetate,  which  blackens  when  held  in  the  mouth  of  the  tube  : 

H2S03    +    6H  H2S     +     3H2O. 

3.  Add  to  a  few  drops  of  the  sulphite  solution  about  2  c.c.  of  silver 
nitrate  solution.     A  white  precipitate  of   silver  sulphite  is   formed, 
which  darkens  on  heating,  due  to  reduction  to  metallic  silver : 

Ag2S03     +     H20  2Ag     +     H2S04. 

Silver  sulphite  is  soluble  in  an  excess  of  the  sulphite  solution. 

4.  A  strip  of  filter-paper,  moistened  with  mercurous  nitrate  solu- 
tion, turns  black  when  suspended  in  sulphur  dioxide,  due  to  reduction 
to  metallic  mercury  : 

2HgN03  +  2H20  +  S02  =  2Hg  +  H2SO4  +  2HNO3. 

Tests  1  and  4,  along  with  the  odor  of  sulphur  dioxide,  are  usually  suf- 
ficient to  recognize  sulphurous  acid  or  sulphites. 

Sulphur  trioxide,  SO3  (Sulphuric  acid  anhydride).  This  is 
a  white,  silk-like  solid  substance,  having  a  powerful  affinity  for 
water;  it  may  be  obtained  by  the  action  of  phosphoric  oxide  on 
strong  sulphuric  acid,  or  by  passing  sulphur  dioxide  and  oxygen 
together  over  heated  platinum-sponge.  It  is  now  made  on  the  large 
scale  by  the  latter  method  for  producing  fuming  sulphuric  acid. 

Sulphuric  acid,  Acidum  sulphuricum,  H2SO4,  SO2(OH)2^  97.35 

(0 if  of  vitriol).     There  is  no  other  acid,  and  perhaps  no  other  sub- 


SULPHUR.  209 

stance,  manufactured  by  chemical  action  which  is  so  largely  used  in 
chemical  operations  and  in  the  manufacture  of  so  many  of  the  most 
important  articles,  as  is  sulphuric  acid. 

Impure  sulphuric  acid  was  known  in  the  eighth  century ;  in  the 
fifteenth  a  purer  acid  was  obtained  by  heating  ferrous  sulphate  (green 
vitriol)  in  a  retort.  To  the  liquid  distilling  over  the  name  of  oil  of 
vitriol  was  given,  in  allusion  to  its  tl.ick  or  oily  appearance  and  the 
green  vitriol  from  which  it  was  obtained.  The  change  is  shown  in 
the  following  reaction  : 

4FeSO4  +  H2O  =  2Fe2O3  +  2SO.,  +  H2SO4.S03. 

Sulphuric  acid  is  found  in  nature  in  combination  with  metals  as 
sulphates.  Thus  calcium  sulphate  (gypsum),  barium  sulphate  (heavy- 
spar),  magnesium  sulphate  (Epsom  salt),  and  others  occur  in  nature. 

Manufacture  of  sulphuric  acid.  Sulphuric  acid  is  manufactured 
on  a  very  large  scale  by  passing  into  large  leaden  chambers  simul- 
taneously, the  vapors  of  sulphur  dioxide  (obtained  by  burning  sulphur 
or  pyrites  in  furnaces),  nitric  acid,  and  steam,  a  supply  of  atmospheric 
air  also  being  provided  for.  The  most  simple  explanation  that  can 
be  given  for  the  manufacture  of  sulphuric  acid  is  the  fact  that  sul- 
phur dioxide  when  treated  with  an  oxidizing  agent,  in  the  presence 
of  water,  is  converted  into  sulphuric  acid : 

S02    +    O    +    H2O    =    H2SO4. 

Only  a  portion  of  the  oxygen  necessary  for  oxidation  is  derived 
from  the  nitric  acid  directly ;  the  larger  quantity  is  obtained  from 
the  atmospheric  air,  the  oxides  of  nitrogen  serving  as  agents  for  the 
transfer  of  the  atmospheric  oxygen. 

By  the  action  of  nitric  acid  on  sulphur  dioxide  and  steam  are  formed  sul- 
phuric acid  and  nitrogen  trioxide : 

2SO2  +  H2O  +  2HNO3  =  2H2SO4  +  N2O3. 

Nitrogen  trioxide  next  takes  up  sulphur  dioxide,  water,  and  oxygen,  forming 
a  compound  called  nitrosyl-sulphuric  acid : 

2SO2  +  N2O3  +  2O  +  H2O  =  2(SO2.OH.NO2). 

This  complex  compound  is  readily  decomposed  by  steam  into  sulphuric  acid 
and  nitrogen  trioxide : 

2(SO2.OH.NO2)  +  H2O  =  2H2S04  +  N2O3 

The  nitrogen  trioxide  again  forms  nitrosyl-sulphuric  acid,  which  again  suffers 

decomposition,  and  so  on  indefinitely,  as  long  as  the  constituents  necessary  for 

the  changes  are  supplied.     These  facts  show  that  a  given  quantity  of  nitric  acid 

will  convert  an  unlimited  amount  of  sulphurous  acid  into  sulphuric  acid. 

14 


210  NON-METALS  AND   THP:iR   COMBINATIONS. 

There  is,  however,  an  unavoidable  loss  of  small  portions  of  nitric  acid,  or 
oxides  of  nitrogen,  for  which  reason  some  nitric  acid  has  to  be  supplied  daily. 
It  is  likely  that  other  chemical  changes  than  the  ones  mentioned  take  place 
in  the  acid  chamber,  but  according  to  modern  investigations  these  are  the 
principal  ones. 

The  liquid  sulphuric  acid  formed  in  the  lead-chamber  collects  at 
the  bottom  of  the  chamber,  whence  it  is  drawn  oif.  In  this  state  it 
is  known  as  chamber  acid  (specific  gravity  1.50),  and  is  not  pure,  but 
contains  about  36  per  cent,  of  water,  and  frequently  either  sulphurous 
or  nitric  acid.  By  evaporation  in  shallow  leaden  pans  it  is  further 
concentrated,  until  it  shows  a  specific  gravity  of  1.72.  When  this 
point  is  reached  the  acid  acts  upon  the  lead,  wherefore  the  further 
concentration  is  conducted  in  vessels  of  glass  or  platinum,  until  a 
specific  gravity  of  1.84  is  obtained.  This  acid  contains  about  95 
per  cent,  of  sulphuric  acid ;  the  remaining  5  per  cent,  of  water  can- 
not be  expelled  by  heat. 

Properties  of  sulphuric  acid.  Pure  acid  has  a  specific  gravity  of 
1.848 ;  it  is  a  colorless  liquid,  of  oily  consistence,  boiling  at  330°  C. 
(626°  F.).  When  cooled  it  forms  crystals,  which  melt  at  10°  C. 
(50°  F.).  When  heated  to  about  160°  C.  (320°  F.),  the  acid  begins 
to  fume  and  gives  off  sulphur  trioxide.  The  100  per  cent,  acid 
gives  off  sulphur  trioxide,  and  diluted  acid  gives  off  water  when 
heated,  until  an  acid  of  98.33  per  cent,  is  reached,  which  boils 
at  the  constant  temperature  of  330°  C.  It  has  a  great  tend- 
ency to  combine  with  water,  absorbing  it  readily  from  atmo- 
spheric air.  Upon  mixing  sulphuric  acid  and  water,  heat  is  gen- 
erated in  consequence  of  the  combination  taking  place  between  the 
two  substances.  To  the  same  tendency  of  sulphuric  acid  to  com- 
bine with  water  must  be  ascribed  its  property  of  destroying 
and  blackening  organic  matter.  It  is  due  to  this  decomposing 
action  of  sulphuric  acid  upon  organic  matter  that  traces  of  the  latter 
color  sulphuric  acid  dark  yellow,  brown,  and,  when  present  in  larger 
quantities,  almost  black.  The  poisonous  caustic  properties  are  due 
to  the  same  action.  (See  Experiments,  page  179.) 

Sulphuric  acid  is  a  very  strong  dibasic  acid,  which  expels  or  dis- 
places most  other  acids ;  its  salts  are  known-  as  sulphates. 

The  sulphuric  acid  of  the  U.  S.  P.  should  contain  not  less  than 
92.5  per  cent,  of  H2SO4,  corresponding  to  a  specific  gravity  of  not 
V>ss  than  1.826  at  25°  C. 

The  diluted  sulphuric  acid,  Acidum  mlphuricum  dilutum,  is  a  mix- 
ture of  100  parts  by  weight  of  acid  and  825  parts  of  water,  or  of 


SULPHUR.  211 

about  60  c.c.  of  acid  and  900  c.c.  of  water.     This  corresponds  to  10 
per  cent,  of  H2SO4,  and  a  specific  gravity  of  1.067  at  25°  C. 

Great  care  should  be  taken  in  diluting  concentrated  sulphuric  acid. 
The  acid  should  always  be  poured  slowly  into  water  with  constant  stir- 
ring. It  is  dangerous  to  pour  the  hot  acid  into  water  and  foolhardy 
to  pour  water  into  the  hot  acid.  Ignorance  or  disregard  of  these  rules 
may  lead  to  sad  consequences. 

When  diluted  sulphuric  acid  acts  on  metals,  hydrogen  is  liberated  and 
escapes  as  a  gas ;  but  if  these  same  metals  are  acted  on  by  concentrated  sul- 
phuric acid,  which  usually  requires  heating,  other  products  are  formed,  such 
as  sulphur  dioxide,  hydrogen  sulphide,  or  sulphur.  This  is  due  to  the  fact 
that  the  concentrated  acid  acts  as  an  oxidizing  agent  toward  the  hydrogen  that 
would  otherwise  be  evolved,  and  itself  is  reduced.  Certain  metals  do  not  act 
on  dilute  sulphuric  acid  at  all,  but  only  on  the  hot  concentrated  acid,  and 
under  these  conditions  hydrogen  is  never  evolved.  This  is  illustrated  in  the 
preparation  of  sulphur  dioxide  by  heating  the  concentrated  acid  with  copper. 
Other  substances,  as  charcoal,  sulphur,  etc.,  that  can  be  oxidized,  act  in  the 
same  way  on  the  hot,  strong  acid. 

Most  sulphates  are  soluble  in  water.  There  are  practically  only  three  which 
are  insoluble  in  water  or  dilute  acids,  namely,  barium,  strontium,  and  lead. 
Calcium  sulphate  is  slightly  soluble  in  water,  and  more  so  in  hydrochloric 
acid.  A  solution  of  it  is  used  as  a  reagent. 

Most  sulphates  are  more  or  less  easily  decomposed  when  heated,  but  those  of 
potassium,  sodium,  lithium,  calcium,  strontium,  and  barium  can  stand  red 
heat. 

Sulphuric  acid,  like  all  dibasic  acids,  has  two  modes  of  ionizing  according 
to  concentration  (see  page  200).  In  more  concentrated  solutions,  the  ions  H* 
and  HSO/  predominate;  in  dilute  solutions,  2H*  and  SO/X  predominate. 
Upon  diluting  a  more  concentrated  solution,  HSO/  ions  dissociate  further, 
thus: 

±H-  +  SO/'. 


The  same  thing  takes  place  when  SO/7  ions  are  removed  by  precipitation, 
which  has  an  effect  equivalent  to  diluting  the  acid. 

Tests  1  and  2  below  are  examples  of  reversible  reactions  that  run  practically 
to  completion,  because  of  the  removal  of  one  of  the  factors  by  precipitation, 
due  to  its  insolubility  (page  114).  These  tests,  like  all  similar  ones  that  fol- 
low, are  explained  in  terms  of  the  ionic  theory  on  pages  193  and  200. 

Tests  for  sulphuric  acid  and  sulphates. 

1.  When  a  solution  of  barium  chloride  is  added  to  dilute  sulphuric 
acid,  or  a  solution  of  any  sulphate,  a  white  precipitate  of  barium 
sulphate  is  obtained,  which  is  insoluble  in  all  dilute  acids : 

Na2S04  +  BaCl2  ==  BaSO4  +  2NaCl 
2Na-  +  SO/'  +  Ba"  +  2C1'  =  BaSO4  +  2Na«  +  2C1'. 


212  NON-METALS  AND   THEIR   COMBINATIONS. 

Usually  this  test  alone  is  sufficient  for  recognition,  as  all  other 
ordinary  barium  salts  are  soluble  in  hydrochloric  or  nitric  acid.  It 
is  very  delicate. 

2.  When   a   solution   of  lead   nitrate    or   acetate  is  employed,  a 
white  precipitate  of  lead  sulphate,  PbSO4  is  obtained.     This  is  solu- 
ble in  a  solution  of  ammonium  acetate. 

3.  Grind  together  in  a  mortar  a  knife-pointful  of  a  sulphate,  sul- 
phur, or  any  compound  containing  it,  with  5  to  10  times  its  bulk  of 
sodium  carbonate  and  about  3  times  its  bulk  of  potassium  cyanide. 
Place  the  mixture  in  a  hole  in  a  piece  of  charcoal  and  heat  with  the 
blow-pipe  flame  until  it  is  thoroughly  fused.     The  mass  now  contains 
yellowish-brown  alkali  sulphide  (hepar),  due  to  reduction  of  the  sul- 
phate by  the  hot  charcoal  and  potassium  cyanide.     The  sodium  car- 
bonate serves  as  &flux,  or  fusing  material. 

Remove  the  mass,  place  it  upon  a  silver  coin,  and  moisten  it  with 
dilute  hydrochloric  acid.  A  black  stain  of  silver  sulphide  will  be 
formed.  This  test  is  of  value  in  the  case  of  insoluble  sulphates  and 
sulphides. 

The  above  procedure  is  known  as  the  charcoal  reduction  test,  and  is 
one  of  the  steps  taken  in  systematic  qualitative  analysis. 

Antidotes.  Magnesia,  sodium  carbonate,  chalk,  and  soap,  to  neutralize 
the  acid. 

Acids  of  sulphur.  While  but  four  oxides  of  sulphur  exist  in  the 
separate  state,  there  are  a  large  number  of  acids  containing  sulphur, 
some  of  which,  however,  are  known  only  as  constituents  of  the 
respective  salts.  The  acids  are  : 

Hyposulphurous  acid,    H2S2O4.  Thiosulphuric  acid,  H2SaOs. 

Sulphurous  acid,  H2SO3.  Dithiouic  acid,  H2S2O6. 

Sulphuric  acid,  H2SO4.  Trithionic  acid,  H2S3O6. 

Pyre-sulphuric  acid,       H2S2O7.  Tetrathionic  acid,  H2S4O6. 

Persulphuric  acid,          H2S2O8.  Pentathionic  acid,  H2S5O6. 

Hydrogen  sulphide,       H2S. 

Pyrosulphuric  acid,  H2S2O7  (Disulphuric  acid,  fuming  sulphuric 
acid,  Nordhausen  oil  of  vitriol).  This  acid  is  made  by  passing  sulphur 
trioxide  (obtained  by  heating  ferrous  sulphate)  into  sulphuric  acid, 
when  direct  combination  takes  place  : 

H2S04    +    S03    =    H2S207. 

It  is  a  thick,  highly  corrosive  liquid,  which  gives  off  dense  fumes 
when  exposed  to  the  air,  and  decomposes  readily  into  sulphur  trioxide 
and  sulphuric  acid  when  heated. 


SULPHUR.  213 

Thiosulphuric  acid,  formerly  Hyposulphurous  acid,  H.2S2O3, 
SO2.SH.OH,  is  of  interest  because  some  of  its  salts  are  used,  as,  for 
instance,  sodium  thiosulphate,  Na2S2O3,  the  sodium  hyposulphite  of 
commerce.  The  acid  itself  is  not  known  in  the  separate  state,  since 
it  decomposes  into  sulphur  and  sulphurous  acid  when  attempts  are 
made  to  liberate  it  from  its  salts. 

Sulphuric  is  the  most  stable  acid  of  sulphur,  and  all  the  others  have  a  tend- 
ency to  pass  to  this  acid.  It  is  for  this  reason  that  both  sulphites  and  thiosul- 
phates  are  good  reducing  agents.  A  solution  of  a  thiosulphate,  when  added 
to  an  acidified  solution  of  potassium  permanganate  or  dichromate,  acts  in  the 
same  way  as  a  sulphite  does.  The  essential  reaction  is : 

Na2S2O3    +    4O    +     H2O    =    Na2S04    +    H2S04. 

Thiosulphates  also  react  with  the  halogen  elements  in  the  manner  shown  by 
this  reaction : 

2Na2S2O3    +     21    =    Na2S406    +    2NaI, 

forming  sodium  tetrathionate  and  sodium  iodide.  This  reaction  is  used  for  the 
quantitative  estimation  of  free  iodine  and  in  the  preparation  of  so-called  de- 
colorized tincture  of  iodine.  It  may  also  be  used  for  removing  iodine  stains 
from  the  skin  or  fabrics. 

Most  of  the  thiosulphates  are  soluble  in  water,  those  of  barium,  lead,  and 
silver  being  only  very  sparingly  soluble.  Alkali  thiosulphates  have  a  marked 
solvent  action  on  many  salts  that  are  insoluble  in  water,  forming  double  thio- 
sulphates. All  thiosulphates  are  decomposed  by  acids. 

Tests  for  thiosulphates. 
(Use  about  a  5  per  cent,  solution  of  sodium  thiosulphate. ) 

1.  The  solution,  upon  addition  of  dilute  sulphuric  or  hydrochloric 
acid,  liberates  sulphur  dioxide,  while  sulphur  is  precipitated  more  or 
less  rapidly,  according  to  the  concentration  and  temperature.     The 
formation  of  these  two  products  is  characteristic  and  the  test  is  suffi- 
cient for  recognition  of  a  thiosulphate.     The  precipitate  of  sulphur 
distinguishes  it  from  a  sulphite. 

2.  Addition   of  silver  nitrate  gives  a  white  precipitate  of  silver 
thiosulphate,  Ag2S2O3,  which  is  immediately  dissolved  if  the  sodium 
thiosulphate  is  in  excess.     The  precipitate  is  rather  unstable,  and 
decomposes  on  standing,  and  more  rapidly  on  heating,  giving  black 
silver  sulphide  and  sulphuric  acid, 

Ag2S203    +    H20  Ag2S    +    H2S04. 

Addition  of  solution  of  lead  nitrate  or  acetate  to  thiosulphate  solution 
gives  similar  results.  Most  thiosulphates  are  unstable,  like  those  of 
silver  and  lead. 


214  NON-METALS  AND   THEIR  COMBINATIONS. 

3.  Barium  chloride  solution  gives  a  white  precipitate  of  barium 
thiosulphate,  BaS2O3-  Calcium  chloride,  however,  gives  no  precipi- 
tate, whereas  with  a  sulphite  a  precipitate  is  formed. 

Persulplmric  acid,  H2S208,  is   obtained  by  passing   an   electric  current 
through  sulphuric  acid  of  a  specific  gravity  1.3  to  1.5.    The  reaction  is 
2H2S04  =  2H  +  H2S208. 

The  ammonium  or  potassium  salts  of  this  acid  are  obtained  by  the  electrol- 
ysis of  saturated  solutions  of  the  bisulphates  of  the  metals,  thus : 
2KHS04  =  K2S208  +  H2. 

Persulphuric  acid  and  its  salts  act  as  strong  oxidizing  agents,  liberating, 
for  instance,  chlorine  from  hydrochloric  acid  or  from  chlorides. 

Hydrogen  sulphide,  H2S  (Sulphuretted  hydrogen).  This  compound 
has  been  mentioned  as  being  liberated  by  the  decomposition  of  organic 
matter  (putrefaction)  and  as  a  constituent  of  some  spring  waters.  It 
is  formed  also  during  the  destructive  distillation  of  organic  matter 
containing  sulphur.  The  best  mode  of  obtaining  it  is  the  decomposi- 
tion of  metallic  sulphides  by  diluted  sulphuric  or  hydrochloric  acid. 
Ferrous  sulphide  is  usually  selected  for  decomposition  : 
FeS  +  H2SO,  =  FeS04  +  HJ3. 

Experiment  15.  Use  apparatus  shown  in  Fig.  42,  page  207.  Place  about  20 
grammes  of  ferrous  sulphide  in  the  flask,  cover  the  pieces  with  water,  and  add 
sulphuric  or  hydrochloric  acid.  Pass  a  portion  of  the  washed  gas  into  water, 
another  portion  into  ammonia  water.  Use  the  solutions  for  the  tests  mentioned 
below.  Ignite  the  gas  at  the  delivery  tube  and  notice  that  sulphur  is  deposited 
upon  the  surface  of  a  cold  plate  held  in  the  flame.  Place  the  apparatus  in  the 
fume  chamber  during  the  operation.  How  much  ferrous  sulphide  is  required 
to  liberate  a  quantity  of  hydrogen  sulphide  sufficient  to  convert  1000  grammes 
of  10  per  cent,  ammonia  water  into  ammonium  sulphide  solution?  The  reac- 
tion taking  place  is  this : 

2NH3    +    H2S    =    (NHJ2S. 

Hydrogen  sulphide  is  a  colorless  gas,  having  an  exceedingly  offen- 
sive odor  and  a  disgusting  taste.  Water  absorbs  about  three  volumes 
of  the  gas,  and  this  solution  is  feebly  acid.  It  is  highly  combustible 
in  air,  burning  with  a  blue  flame,  and  forming  sulphur  dioxide  and 
water.  It  is  directly  poisonous  when  inhaled,  its  action  depending 
chiefly  on  its  power  of  reducing,  and  combining  with,  the  blood- 
coloring  matter.  Plenty  of  fresh  air,  or  air  containing  a  very  little 
chlorine,  should  be  used  as  an  antidote. 

Hydrogen  sulphide  can  be  driven  completely  from  its  aqueous  solu- 
tion by  heating.  It  is  a  rather  unstable  compound,  being  easily 
broken  up  into  its  constituents.  For  this  reason  it  is  a  good  reduc- 


SULPHUR.  215 

ing  agent.  For  example,  sulphur  dioxide  is  reduced  by  it  to  sulphur, 
but  is  not  affected  by  free  hydrogen  gas  : 

2H2S  +  SO2  =  2H2O  +  38. 

It  is  probable  that  native  sulphur  found  in  volcanic  regions  is  produced 
in  this  way.  Because  of  the  instability  of  the  gas,  its  sulphur  often 
acts  like  sulphur  in  the  free  state.  Thus,  the  metals  from  potassium 
to  silver  inclusive  in  the  electrochemical  series  (see  page  198)  soon 
become  tarnished  with  a  layer  of  sulphide  when  exposed  to  the  gas  : 

2Ag  +  H2S  =  Ag2S  +  2H. 

The  solution  of  hydrogen  sulphide  is  slowly  affected  by  oxygen  of  the 
air  with  precipitation  of  sulphur,  H2S  -f  O  —  H2O  -f  S.  Hence, 
it  does  not  keep  except  in  full  bottles.  In  solution  it  is  a  dibasic 
acid  of  extremely  weak  character,  only  0.07  per  cent,  of  the  molecules 
being  dissociated,  mainly  according  to  this  equation  : 

H2S  7±  H-  +  HS'. 

The  ion  HS'  also  dissociates,  but  to  a  less  degree  even  than  water : 

HS'^±H-  +  S". 

Hydrogen  sulphide,  like  any  dibasic  acid,  can  give  two  kinds  of  salts, 
acid  and  normal ;  for  example,  sodium  hydrosulphide,  NaHS,  and 
sodium  sulphide,  Na2S.  The  acid  salt  is  obtained  in  solution,  when 
hydrogen  sulphide  is  passed  into  a  solution  of  sodium  hydroxide  to 
saturation.  It  has  a  neutral  reaction  : 

NaOH  +  H2S  =  NaHS  +  H2O. 
In  solution  it  dissociates,  thus  : 

NaHS  7±  Na-  +  HS'. 

The  normal  salt,  Na2S,  does  not  exist  in  solution,  but  can  be  obtained 
in  the  dry  state  by  adding  to  the  acid  salt  an  amount  of  alkali  equal 
to  that  used  in  making  the  same,  and  evaporating  to  dry  ness : 

NaHS  4-  NaOH  =  Na2S  -f  H2O. 

When  the  dry  salt  is  dissolved  in  water,  it  is  completely  hydrolyzed 
into  the  acid  salt  and  free  alkali,  and,  therefore,  has  a  strong  alkaline 

reaction  : 

Na2S  +  H20  =  NaHS  +  NaOH. 

Hydrogen  sulphide  gas  and  its  solution  in  water  are  frequently 
used  as  reagents  in  analytical  chemistry  for  precipitating  and  recog- 
nizing metals.  This  use  depends  on  the  property  of  the  sulphur  to 


216  NON-METALS  AND  THEIR   COMBINATIONS. 

combine  with  many  metals  to  form  insoluble  compounds,  the  color 
of  which  frequently  is  very  characteristic  : 

CuS04  +  H2S  =  CuS  +  H2S04. 

The  sulphides  that  are  insoluble  in  water  fall  approximately  into  three 
groups: 

1.  Those  that  are  almost  completely  insoluble  in  water,  such  as  the  sul- 
phides of  lead,  copper,  bismuth,  silver,  mercury,  arsenic,  antimony,  tin,  and  a 
few  others.     These,  moreover,  are  not  dissolved  by  dilute  acids,  and  hence  are 
precipitated  from  solutions  of  salts  of  the  metals  bypassing  hydrogen  sulphide 
into  them  even  when  a  little  free  acid  is  present : 

Pb(N03)2      +       H2S       =       PbS       +       2HN03, 
Lead  sulphide. 

or         Pb"  +  2(N03)'  +  2H-  +  S"  =  PbS  +  2H-  +  2(NO3)'. 

2.  Those  that  are  practically  insoluble  in  water,  yet  more  soluble  than  the 
sulphides  of  group  1,  and  are  dissolved  by  even  very  dilute  active  acids.     The 
metals  iron,  cobalt,  nickel,  manganese,  zinc,  and  a  few  others  form  such  sul- 
phides.    Some  of  these  sulphides  are  so  readily  soluble  in  dilute  acids  that  they 
are  prevented  from  being  precipitated  by  hydrogen  sulphide  by  the  acid  that 
would  be  liberated  in  the  reaction  (see  equation  above).     In  the  case  of  zinc 
salts  partial  precipitation  takes  place  until  equilibrium  is  reached,  but  if  some 
free  acid  is  present,  no  precipitation  takes  place.     To  form  the  sulphides  of 
this  group,  a  salt  of  hydrogen  sulphide,  such  as  ammonium  or  sodium  sul- 
phide, is  applied  to  neutral  solutions  of  the  salts  of  the  metals,  thus  : 

FeS04       +       (NH4)2S       =       FeS       +       (NH4)2SO4, 
Iron  sulphide. 

or          Fe"  +  S04"  +  2(NH4)«  +  S"  =  FeS  +  2(NH4)-  -f  SO4". 

3.  Those  that  are  known  only  in  the  dry  state,  and  although  they  are  insol- 
uble as  such  in  water,  yet  they  dissolve  because  they  are  hydrolyzed  into  solu- 
ble products,  thus : 

2CaS  -f  2H20  =  Ca(OH)2  +  Ca(SH)2. 

The  sulphides  of  barium,  strontium,  and  calcium  belong  to  this  class.  They 
cannot  be  precipitated,  either  by  hydrogen  sulphide  or  ammonium  sulphide. 
They  are  generally  made  from  the  sulphate  by  heating  with  carbon  (reduction 
to  sulphide). 

Solutions  of  normal  sulphides,  as  Na2S,  and  acid  sulphides,  as  NaHS,  or 
NH4HS,  when  used  as  reagents  in  precipitation  of  insoluble  sulphides,  give 
the  same  results  because  of  the  presence  of  S/x  ions,  which  unite  with  the  ions 
of  the  other  metals. 

Tests  for  hydrogen  sulphide  or  sulphides. 
1.  Hydrogen  sulphide  or  soluble  sulphides  (ammonium  sulphide 
may  be  used)  when  added  to  soluble  salts  of  lead,  copper,  mercury, 
etc.,  give  black  precipitates  of  the  sulphides  of  those  metals. 
^  2.  From  insoluble  sulphides  (ferrous  sulphide,  FeS,  may  be  used) 
liberate  the  gas  by  dilute  sulphuric  or  hydrochloric  acid,  and  test  as 


SULPHUR.  217 

above,  or  suspend  a  piece  of  filter-paper,  moistened  with  solution  of 
lead  acetate,  in  the  liberated  gas,  when  the  paper  turns  dark.  Some 
sulphides,  for  instance,  those  of  mercury,  gold,  platinum,  as  also  FeS2, 
and  a  few  others,  are  not  decomposed  by  the  acids  mentioned,  unless 
zinc  be  added. 

Carbon  disulphide,  Carbonei  disulphidum,  CS2  —  75.57.  This 
com  pound  is  obtained  by  passing  vapors  of  sulphur  over  heated 
charcoal.  It  is  a  colorless,  highly  refractive,  very  volatile,  and 
inflammable  neutral  liquid,  having  a  characteristic  odor  and  a  sharp, 
aromatic  taste.  It  boils  at  46°  C.  (115°  F.) ;  it  is  almost  insoluble 
in  water,  soluble  in  alcohol,  ether,  chloroform,  fixed  and  volatile  oils ; 
for  the  latter  two  it  is  an  excellent  solvent,  but  dissolves,  also,  many 
other  substances,  such  as  sulphur,  phosphorus,  iodine,  many  alka- 
loids, etc. 

Selenium,  Se,  and  Tellurium,  Te,  are  but  rarely  met  with.  Both  elements 
show  much  resemblance  to  sulphur;  both  are  polymorphous;  both  combine 
with  hydrogen,  forming  H.2Se  and  H2Te,  gaseous  compounds  having  an  odor 
more  disagreeable  even  than  that  of  H2S.  Like  sulphur,  they  form  dioxides. 
Se02  and  TeO2,  which  combine  with  water,  forming  the  acids  H2SeO3  and 
H2Te03,  analogous  to  H2SO3.  The  acids  H2Se04  and  H9TeO4,  corresponding 
to  H2SO4,  also  are  known. 

Ionic  mechanism  of  the  solution  by  acids  of  salts  that  are  insol- 
uble in  water.  The  operation  of  dissolving  by  the  aid  of  an  acid,  salts  that 
are  insoluble  in  water  is  resorted  to  frequently  in  general  chemical  work,  and 
particularly  in  chemical  analysis.  It  is  a  matter  of  observation,  too,  that  a 
salt  will  dissolve  in  some  acids,  but  not  in  others;  also  that  of  salts  of  the  same 
acid  with  different  metals,  some  will  dissolve  in  a  given  acid,  while  others  will 
not.  Thus  zinc  sulphide  is  soluble  in  dilute  hydrochloric  acid,  but  not  in 
acetic,  and  the  same  is  true  of  calcium  oxalate  and  calcium  phosphate.  Iron 
sulphide  is  soluble  in  most  any  dilute  acid,  but  copper  sulphide  is  not  appre- 
ciably dissolved  by  the  same  acids.  The  student  often  wonders  what  the  ex- 
planation is  of  such  facts  as  these.  The  ionic  theory  gives  a  physical  basis  for 
accounting  for  them. 

Solution  is  the  converse  of  precipitation.  In  the  discussion  of  the  latter 
subject  (see  page  193)  it  is  stated  that  whenever  there  are  more  ions  of  a  sub- 
stance than  a  saturated  solution  of  that  substance  can  maintain,  the  excess  of 
ions  unite  to  molecules,  which  separate  from  solution  as  a  precipitate.  The 
more  insoluble  the  substance  is  the  smaller  is  the  concentration  of  molecules 
and  ions  that  can  be  maintained  in  its  saturated  solution,  and  the  more  com- 
plete is  the  precipitation.  Every  "insoluble"  substance  is  soluble  to  some 
extent  in  water,  even  if  only  minutely.  But  many  of  the  so-called  insoluble 
salts  are  slightly  soluble  in  water,  which  is  an  important  factor  in  accounting 
for  the  solution  of  salts  by  acids.  Now,  water  in  contact  with  such  a  salt  be- 


218  NON-METALS  AND   THEIR  COMBINATIONS. 

comes  saturated,  that  is,  it  takes  up  the  maximum  number  of  molecules  and 
ions  that  it  can  hold  (which,  of  course,  is  not  large),  and  these  are  in  equi- 
librium. If  in  any  way  the  concentration  of  the  negative  (acid  radical)  ion  is 
diminished,  more  molecules  dissociate  to  keep  up  the  concentration  of  that 
ion,  which  results  in  the  dissolving  of  more  molecules  of  the  solid  salt  to  keep 
up  saturation  and  equilibrium.  If  the  negative  ions  of  the  salt  are  of  an  acid 
that  has  a  slight  dissociating  power,  their  concentration  will  be  diminished 
when  an  active  (highly  dissociating)  acid  is  added  to  the  mixture,  thereby 
furnishing  an  abundance  of  H'  ions,  with  which  the  negative  ions  of  the  salt 
unite  to  form  undissociated  molecules  of  the  acid.  If  the  concentration  of  the 
negative  ions  of  the  salt  is  greater  than  that  which  can  be  maintained  by  the 
corresponding  acid,  the  salt  will  dissolve  by  the  addition  of  an  active  acid,  in 
keeping  with  the  principle  of  equilibrium  as  involved  in  the  dissociation  con- 
stant (see  page  192).  Even  an  acid  of  a  moderate  degree  of  dissociation  may 
have  its  dissociation  reversed  to  such  an  extent  in  the  presence  of  an  excess 
of  a  highly  dissociating  acid,  like  hydrochloric,  that  it  becomes  equivalent  to 
a  slightly  dissociating  acid,  and  does  not  maintain  as  great  a  concentration  of 
its  negative  ion  as  is  maintained  by  its  slightly  soluble  salts  in  water.  This  is 
illustrated  by  the  solution  of  calcium  oxalate  in  excess  of  hydrochloric  acid. 
In  the  case  of  highly  insoluble  salts,  like  barium  sulphate,  the  amount  dis- 
solved, and  consequently  the  concentration  of  its  ions,  is  so  extremely  small 
that  addition  of  active  acids  has  very  little  effect  in  reducing  the  concentration 
of  the  negative  ion.  Hence,  extremely  little  of  such  a  salt  is  dissolved  by 
acids.  Such  salts  evidently  can  be  precipitated  in  an  acid  medium,  whereas 
the  salts  that  are  dissolved  by  a  given  acid  cannot  be  precipitated  in  the 
presence  of  that  acid. 

The  points  just  discussed  may  be  given  a  more  concrete  form  by  the  consid- 
eration of  the  sulphide  of  iron  and  of  copper.  When  dilute  hydrochloric  acid 
is  added  to  iron  sulphide,  hydrogen  sulphide  is  evolved.  The  ionic  repre- 
sentation of  the  act  of  solution  is  the  following : 

FeS  (slightly  soluble)  ^±  Fe'  •     +     S"     \  —  R  s 
2HC1  ^±  2Cr     +     2H'  /  " 

The  negative  ion  S"  coming  from  the  slight  amount  of  FeS  dissolved  in  water 
is  also  the  ion  of  H2S.  Hydrogen  sulphide  dissociates  to  a  less  degree  than 
does  FeS ;  that  is,  the  concentration  of  Sx/  that  can  be  maintained  by  H2S  in 
solution  is  less  than  that  which  can  be  maintained  by  FeS  in  solution.  The 
result  is  that  some  Sx/  ions  unite  with  H'  ions  of  the  hydrochloric  acid  to 
form  undissociated  molecules  of  HaS,  thus  reducing  the  concentration  of  S/x 
ion.  More  FeS  dissolves  to  keep  up  the  equilibrium.  This  is  kept  up  until 
all  the  FeS  is  dissolved,  or  until  (if  FeS  is  in  excess)  the  HC1  is  so  much  ex- 
hausted that  the  little  which  remains  is  in  equilibrium  with  the  other  products. 
As  the  H,S  accumulates,  the  solution  becomes  saturated  and  the  excess  escapes 
as  gas. 

In  the  case  of  copper  sulphide,  dilute  hydrochloric  acid  has  no  action.  The 
ionic  reactions  would  be : 

CuS  (very  slightly  soluble)  \  ;±  Cu'  •     +  S"    \  _^  R  ~ 
2HC1  /  i±  2C1'      +  2H'  /  *~     2 


PHOSPHORUS.  219 

But  the  concentration  of  S/x  ions  maintained  by  CuS  in  solution  is  less  than 
that  maintained  by  H2S  in  solution,  even  in  the  presence  of  the  excess  of  H- 
ions  of  the  dilute  hydrochloric  acid,  which  repress  to  some  extent  the  disso- 
ciation of  H2S.  Hence,  not  only  is  there  no  solution  of  the  copper  sulphide, 
but  if  H2S  is  passed  into  an  acidified  solution  of  a  copper  salt,  CuS  is  precipi- 
tated. Only  a  rather  concentrated  solution  of  hydrochloric  acid  will  so  far 
reduce  the  concentration  of  Sx/  ions  as  to  allow  the  copper  sulphide  to 
dissolve. 

The  subject  may  be  summed  up  in  a  general  statement,  thus :  The  difficultly 
soluble  salts  of  weaker  (less  ionized)  acids  are,  as  a  rule,  dissolved  by  solutions 
of  the  stronger  (more  ionized)  acids.  Exceptions  are  salts  of  extreme  insolubility 
of  stronger  acids,  and,  in  a  few  cases,  even  of  weaker  acids. 

17.  PHOSPHORUS. 

pi»  =  31  (30.77). 

Occurrence  in  nature.  Phosphorus  is  found  in  nature  chiefly  ID 
the  form  of  phosphates  of  calcium  (apatite,  phosphorite),  iron,  and 
aluminum,  which  minerals  form  deposits  in  some  localities,  but-  occur 
also  diffused  in  small  quantities  through  all  soils  upon  which  plants 
will  grow,  phosphorus  being  an  essential  constituent  of  the  food  of 
most  plants.  Through  the  plants  it  enters  the  animal  system,  where 
it  is  found  either  in  organic  compounds,  or — and  this  in  by  far  the 
greater  quantity — as  tricalcium  phosphate  principally  in  the  bones, 
which  contain  about  60  per  cent,  of  it.  From  the  animal  system  it 
is  eliminated  chiefly  in  the  urine. 

Manufacture  of  phosphorus.  Phosphorus  was  discovered  and 
made  first  in  1669  by  Brandt,  of  Hamburg,  Germany,  who  obtained 
it  in  small  quantities  by  distilling  urine  previously  evaporated  and 
mixed  with  sand. 

QUESTIONS. — How  is  sulphur  found  in  nature?  Mention  of  sulphur: 
atomic  weight,  valence,  color,  odor,  taste,  solubility,  behavior  when  heated, 
and  allotropic  modifications.  State  the  processes  for  obtaining  sublimed, 
washed,  and  precipitated  sulphur.  State  composition  and  mode  of  preparing 
sulphur  dioxide  and  sulphurous  acid ;  what  are  they  used  for,  and  what  are 
their  properties  ?  Explain  the  process  for  the  manufacture  of  sulphuric  acid 
on  a  large  scale.  Mention  of  sulphuric  acid  :  color,  specific  gravity,  its  action 
on  water  and  organic  substances.  Give  tests  for  sulphates  and  sulphites,  sul- 
phuric and  sulphurous  acids.  What  is  the  difference  between  sulphates,  sul- 
phites, and  sulphides?  How  is  hydrogen  sulphide  formed  in  nature,  and  by 
what  process  is  it  obtained  artificially  ?  What  are  its  properties,  and  what  is 
it  used  for?  Mention  antidotes  in  case  of  poisoning  by  sulphuric  acid  and 
hydrogen  sulphide. 


220  NON-METALS  AND   THEIR  COMBINATIONS. 

The  manufacture  of  phosphorus  to-day  depends  on  the  deoxida- 
tion  of  metaphosphoric  acid  by  carbon  at  a  high  temperature  in 
retorts. 

The  acid  is  obtained  by  adding  to  any  suitable  tricalcium  phophate  sulphuric 
acid  in  a  quantity  sufficient  to  combine  with  the  total  amount  of  calcium 
present.  The  first  action  of  sulphuric  acid  upon  the  phosphate  consists  in  a 
removal  of  only  two-thirds  of  the  calcium  present,  and  the  formation  of  an 
acid  phosphate : 

CagCPOJa  +  3HaSO4  =  CaH4(PO4)2  -f  2CaSO4  +  H2SO4. 

The  nearly  insoluble  calcium  sulphate  is  separated  by  filtration,  and  the 
solution  of  acid  phosphate  containing  free  sulphuric  acid  is  evaporated  to  the 
consistency  of  a  syrup,  when  more  calcium  sulphate  separates  and  a  solution 
of  nearly  pure  phosphorig  acid  is  left : 

CaH4(PO4)2  +  H2SO4  =  CaS04  -f  2(H3POJ. 

This  syrupy  phosphoric  acid  is  mixed  with  coal  and  heated  to  a  temperature 
sufficiently  high  to  expel  water  and  convert  the  ortho-  into  meta-phosphoric 
acid: 

2(H3POJ  =  2HPO3  +  2H2O. 

The  dry  solid  mixture  of  this  acid  and  charcoal  is  now  introduced  into 
retorts  and  heated  to  a  strong  red  heat,  when  the  following  decomposition 
takes  place : 

2(HP03)  +  50  =  H20  +  SCO  +  2P. 

The  three  products  formed  escape  in  the  form  of  gases  from  the  retort,  and  by 
passing  them  through  cold  water  phosphorus  is  converted  into  a  solid.  The 
reaction  in  the  retorts  is  somewhat  more  complicated  than  above  stated  in  the 
equation,  as  some  gaseous  hydrogen  phosphide  and.  a  few  other  products  are 
formed  in  small  quantities. 

Also  phosphorus  is  now  made  by  subjecting  to  the  action  of  a  strong  electric 
current  a  mixture  of  tricalcium  phosphate  and  carbon,  when  phosphorus  is  set 
free,  while  calcium  carbide  and  carbonic  oxide  are  formed : 

Ca,(PO4)2  +  140  =  2P  +  3CaC2  -4-  SCO. 

Properties  of  phosphorus.  When  recently  prepared,  phos- 
phorus is  a  colorless,  translucent,  solid  substance,  which  has  some- 
what the  appearance  and  consistency  of  bleached  wax.  In  the 
course  of  time,  and  especially  on  exposure  to  light,  it  becomes  by 
degrees  less  translucent,  opaque,  white,  yellow,  and  finally  yellowish- 
red.  At  the  freezing-point  phosphorus  is  brittle  ;  as  the  temperature 
increases  it  gradually  becomes  softer,  until  it  fuses  at  44°  C.  (111°F.), 
forming  a  yellowish  fluid,  which  at  290°  C.  (554°  F.)  (in  the  absence 
of  oxygen)  is  converted  into  a  colorless  vapor.  Specific  gravity  1.83 
at  10°  C.  (50°  F.) 

The  most  characteristic  features  of  phosphorus  are  its  great  affinity 
for  oxygen,  and  its  luminosity,  visible  in  the  dark,  from  which 


PHOSPHORUS.  221 

latter  property  its  name,  signifying  "  carrier  of  light,"  has  been 
derived.  In  consequence  of  its  affinity  for  oxygen,  phosphorus  has 
to  be  kept  under  water,  as  it  invariably  takes  fire  when  exposed  to 
the  air,  the  slow  oxidation  taking  place  upon  the  surface  of  the 
phosphorus  soon  raising  it  to  50°  C.  (122°  F.)  at  which  temperature 
it  ignites,  burning  with  a  bright  white  flame,  and  giving  off  dense, 
white  fumes  of  phosphoric  oxide.  The  luminosity  of  phosphorus, 
due  to  this  slow  oxidation,  is  seen  when  a  piece  of  it  is  exposed  to 
the  air,  and  whitish  vapors  are  emitted  which  are  luminous  in  the 
dark  ;  at  the  same  time  an  odor  resembling  that  of  garlic  is  noticed. 

Phosphorus  is  insoluble  in  water,  sparingly  soluble  in  alcohol, 
ether,  fatty  and  essential  oils,  very  soluble  in  chloroform  and  in 
disulphide  of  carbon,  from  which  solution  it  separates  in  the  form  of 
crystals. 

Although  nitrogen  has  very  weak  chemical  affinities,  while  those 
of  phosphorus  are  extremely  strong,  yet  there  is  a  close  resemblance 
in  the  chemical  properties  of  these  two  elements.  Both  are  chiefly 
either  trivalent  or  quinquivalent;  both  form  compounds  corresponding 
to  one  another  in  composition,  as  also  in  properties.  Thus  we  know 
the  two  gaseous  compounds  NH3  and  PH3 ;  the  oxides  N2O3,  N2O5, 
and  P2O3,  P2O5.  There  is  also  metaphosphoric  acid,  HPO3,  corre- 
sponding to  nitric  acid,  HNO3.  The  chlorides  NC13  and  PC13  are 
known,  and  many  other  corresponding  features  may  be  pointed  out 
It  will  be  shown  later  that  nitrogen  and  phosphorus  have  a  great 
resemblance  to  the  metallic  elements  arsenic  and  antimony. 

Phosphorus  not  only  combines  directly  with  oxygen,  but  also  with 
chlorine,  bromine,  iodine,  sulphur,  and  with  many  metals,  the  latter 
compounds  being  known  as  phosphides. 

Phosphorus  is  trivalent  in  some  compounds,  as  in  PC13,  P2O3 ; 
quinquivalent  in  others,  as  in  PC15,  P2O6. 

The  molecules  of  most  elements  contain  two  atoms ;  phosphorus  is 
an  exception  to  this  rule,  its  molecule  containing  four  atoms.  The 
molecular  weight  of  phosphorus  is  consequently  4  X  30.77  =  123.08. 

Allotropic  modifications.  Several  allotropic  modifications  of 
phosphorus  are  known,  of  which  the  red  phosphorus  (frequently 
called  amorphous  phosphorus)  is  the  most  important.  This  variety  is 
obtained  by  exposing  common  phosphorus  for  some  time  to  a  tem- 
perature of  260°  C  (500°  F.),  in  an  atmosphere  of  carbon  dioxide. 
The  change  takes  place  rapidly  when  a  higher  temperature  is  used 
and  pressure  is  applied.  This  modified  phosphorus  is  a  red  powder, 
which  differs  widely  from  common  phosphorus.  It  is  not  poisonous. 


222  NON-METALS  AND   THEIR   COMBINATIONS. 

not  luminous,  not  soluble  in  the  solvents  above  mentioned,  not  com- 
bustible until  it  has  been  heated  to  about  280°  C  (536°  F.),  when  it 
is  reconverted  into  common  phosphorus. 

Use  of  phosphorus.  By  far  the  largest  quantity  of  all  phos- 
phorus (both  common  and  red)  is  used  for  matches,  which  are  made 
by  dipping  wooden  splints  into  some  combustible  substance,  as 
melted  sulphur  or  paraffin,  and  then  into  a  paste  made  by  thoroughly 
mixing  phosphorus  with  glue  in  which  some  oxidizing  agent  (potas- 
sium nitrate  or  chlorate)  has  been  dissolved. 

The  so-called  "  safety  matches"  contain  a  mixture  of  antimony  trisulphide, 
red  lead,  and  the  chlorate  and  dichromate  of  potassium.  This  mixture  will  not 
ignite  by  simple  friction,  but  does  so  when  drawn  across  a  surface  upon  which 
is  a  mixture  of  red  phosphorus  and  antimony  pentasulphide. 

Pharmaceutical  preparations  containing  phosphorus  in  the  elementary  state 
are  phosphorated  oil,  pills  of  phosphorus,  and  spirit  of  phosphorus.  The  second 
is  official. 

Phosphorus  is  also  used  for  making  phosphoric  acid  and  other  compounds. 

Poisonous  properties  of  phosphorus ;  antidotes.  Common  phosphorus  is 
extremely  poisonous,  two  kinds  of  phosphorus-poisoning  being  distinguished. 
They  are  the  acute  form,  consequent  upon  the  ingestion  of  a  poisonous  dose, 
and  the  chronic  form  affecting  the  workmen  employed  in  the  manufacture  of 
phosphorus  or  of  lucifer  matches. 

In  cases  of  poisoning  by  phosphorus,  efforts  should  be  made  to  eliminate  the 
poison  as  rapidly  as  possible  by  means  of  stomach-pump,  emetics,  or  cathartics. 
As  antidote  a  one-tenth  per  cent,  solution  of  potassium  permanganate  has  been 
used  successfully;  it  acts  by  oxidizing  the  phosphorus,  converting  it  into 
ortho-phosphoric  acid.  Oil  of  turpentine  has  also  been  used  as  an  antidote, 
though  its  action  has  not  been  sufficiently  explained.  Oil  or  fatty  matter 
(milk)  must  not  be  given,  as  they  act  as  solvents  of  the  phosphorus,  causing  its 
more  ready  assimilation. 

Detection  of  phosphorus  in  cases  of  poisoning.  Use  is  made  of  its  luminous 
properties  in  detecting  phosphorus,  when  in  the  elementary  state.  Organic 
matter  (contents  of  stomach,  food,  etc.)  containing  phosphorus  will  often  show 
this  luminosity  when  agitated  in  the  dark.  If  this  process  fails,  in  consequence 
of  too  small  a  quantity  of  the  poison,  a  portion  of  the  matter  to  be  examined 
is  rendered  fluid  by  the  addition  of  water,  slightly  acidulated  with  sulphuric 
acid,  and  placed  in  a  flask,  which  is  connected  with  a  bent  glass  tube  leading 
to  a  Liebig's  condenser.  The  apparatus  (Fig.  43)  is  placed  in  the  dark,  and 
the  flask  is  heated.  If  phosphorus  be  present,  a  luminous  ring  will  be  seen 
where  the  glass  tube,  leading  from  the  flask,  enters  the  condenser.  The  heat 
should  be  raised  gradually  to  the  boiling-point,  the  liquid  kept  boiling  for 
some  time,  and  the  products  of  distillation  collected  in  a  glass  vessel.  Phos- 
phorus volatilizes  with  the  steam,  and  small  globules  of  it  may  be  found  in  the 
collected  fluid.  If,  however,  the  quantity  of  phosphorus  in  the  examined 
matter  was  very  small,  it  may  all  have  become  oxidized  during  the  distillation, 
and  the  fluid  will  then  contain  phosphorous  acid,  the  tests  for  which  will  be 
stated  below. 


PHOSPHORUS.  223 

It  should  be  mentioned  that  the  luminosity  of  phosphorus  vapors  is  dimin- 
ished, or  even  prevented,  by  vapors  of  essential  oils  (oil  of  turpentine,  for 
instance),  ether,  olefiant  gas,  and  a  few  other  substances. 

Oxides  of  phosphorus.  Four  oxides  of  phosphorus  are  known. 
They  are  phosphorus  monoxide,  P4O,  phosphorus  trioxidc,  P2O3,  phos- 
phorus tetroxide,  P2O4,  and  phosphorus  pentoxide,  P2O5.  The  three 
lower  oxides  are  obtained  by  slow  oxidation,  or  by  the  burning  of 
phosphorus  in  a  limited  supply  of  air ;  while  the  pentoxide  is  formed 

FIG.  43. 


Apparatus  for  detection  of  phosphorus  in  cases  of  poisoning. 

whenever  phosphorus  burns  under  ordinary  conditions.  The  pent- 
oxide  is  a  white  powder  possessing  an  intense  affinity  for  water, 
with  which  it  combines  to  form  phosphoric  acid,  while  the  trioxide 
with  water  produces  phosphorous  acid. 

Hypophosphorous  acid,  Acidum  hypophosphorosum,  H3PO2, 
PO.H2.OH  =  65.53.  When  phosphorus  is  heated  with  solution  of 
potassium,  sodium,,  or  calcium  hydroxide,  the  hypophosphite  of  these 


224  NON-METALS  AND  THEIR  COMBINATIONS. 

metals  is  formed,  while  gaseous  hydrogen  phosphide,  PH3,  is  lib- 
erated and  ignites  spontaneously.  The  action  may  be  represented 
thus : 

3KOH  +  4P  +  3H20  =  3KPH2O2  +  PH3. 
or 

3Ca(OH)2  +  8P  +  6H2O  =  3Ca(PH2O2)2  +  2PH3. 

From  calcium  hypophosphite  the  acid  may  be  obtained  by  decom- 
posing the  salt  with  oxalic  acid,  which  forms  insoluble  calcium 
oxalate,  while  hypophosphorous  acid  remains  in  solution  : 

Ca(PH202)2  +  H2C204  =  CaC204  +  2HPH2O2. 

From  potassium  hypophosphite  the  acid  may  be  liberated  by  the 
addition  of  tartaric  acid  and  alcohol,  when  potassium  acid  tartrate 
forms,  which  is  nearly  insoluble  in  dilute  alcohol  and  may  be  sepa- 
rated by  filtration. 

Pure  hypophosphorous  acid  is  a  white  crystalline  substance,  acting 
energetically  as  a  deoxidizing  agent.  Although  containing  three 
atoms  of  hydrogen,  it  is  a  monobasic  acid,  only  one  of  the  hydrogen 
atoms  being  replaceable  by  metals. 

Hypophosphorous  acid  of  the  U.  S.  P.  contains  30  per  cent,  and 
the  diluted  acid  10  per  cent,  of  the  pure  acid  dissolved  in  water. 
Both  preparations  are  colorless  acid  liquids,  which,  upon  heating,  lose 
water  and  are  afterward  decomposed  into  phosphoric  acid  and  hydrogen 
phosphide,  which  ignites : 

2H3P02  H3P04    +    PH3. 

Similar  to  the  case  of  sulphur,  the  most  stable  acid  of  phosphorus  is  phos- 
phoric acid,  and  the  others  show  a  tendency  to  pass  to  it.  These  are,  therefore, 
easily  oxidized  and  also  easily  reduced.  Thus,  hypophosphorous  acid  is  not 
only  quickly  oxidized  by  the  usual  oxidizing  agents,  but  even  precipitates  many 
metals  from  their  salts.  Hypophosphites,  when  brought  into  the  presence  of 
nascent  hydrogen,  are  reduced  to  phosphine  gas,  PH3  (compare  with  sulphites). 
All  hypophosphites  are  soluble  in  water  and  nearly  all  are  colorless.  About 
six  are  used  in  medicine. 

Tests  for  hypophosphites. 

(Use  about  a  5  per  cent,  solution  of  the  sodium  salt,  NaPH2O2.) 
1.  Heat  a  small  quantity  of  the  dry  sodium  salt  in  a  porcelain  dish 
until  it  ignites.  The  salt  is  decomposed  into  a  phosphate  and  phos- 
phine, which  burns  with  a  characteristic  brilliant  light,  emitting  a 
white  cloud  of  oxide  of  phosphorus.  Some  red  phosphorus  is  also 
formed. 

2NaPH202  =  Na2HPO,  +  PH3. 
2PH3  +  80  =  P205  +  3H20.    2PH3  +  30  =  2P  +  3H,O. 


PHOSPHORUS.  225 

2.  Acidify  about  5  c.c.  of  the  solution  with  dilute  hydrochloric 
acid,  and  add  some  mercuric  chloride  solution.      A  white  precipitate 
of  mercurous  chloride  is  formed.    Above  60°  C.  and  with  excess  of  the 
hypophosphite,  further  reduction  to  dark  metallic  mercury  takes  place. 

4HgCl2  +  Na.PHA  +  2H2O  =  4HgCl  +  H,PO4  +   NaCl  +  3HC1. 
4HgCl  +    NaPHA  +  2H2O  ==  4Hg      +  HSPO4  +  NaCl  +  3HC1. 

3.  Addition  of  silver  nitrate  solution  causes  a  dark  precipitate  of 
metallic  silver.     In  the  first  instant,  a  white  precipitate  of  silver  hypo- 
phosphite  is  seen,  but  this  is  very  unstable. 

NaPH2Q2  +  4AgN03  +  2H2O  ==  4Ag  +  NaH2PO4  +  4HN03. 

4.  When  the  solution  is  added  to  acidified  potassium  permanganate 
solution,  the  latter  is  decolorized.     The  essential  reaction  is  this, 

NaPH202     +     02     =     NaH2P04. 

Tests  1  and  2  are  very  distinctive  and  usually  sufficient  to  recognize 
the  acid  or  its  salts. 

Phosphorous  acid,  H3PO3,  PO.H.(OH)2.  This  is  a  dibasic  acid 
obtained  by  dissolving  phosphorous  oxide  in  water: 

PA    +    3H20    =    2H3P03. 

or  still  better  by  the  action  of  water  on  phosphorus  trichloride : 
PC13  +  3H2O  ==  H3P03   +  3HC1. 

It  is  a  colorless  acid  liquid,  which  forms  salts  known  as  phos- 
phites ;  it  is  a  strong  deoxidizing  agent,  easily  absorbing  oxygen, 
forming  phosphoric  acid. 

Tests.  Phosphorous  acid  and  its  salts  give  practically  the  same 
reactions  as  the  hypophosphites.  The  following  are  the  chief  dis- 
tinctions :  Phosphites  when  added  to  solutions  of  calcium,  barium,  and 
strontium  salts  give  precipitates  of  phosphites  of  these  metals,  whereas 
hypophosphites  do  not  give  a  precipitate.  Acidified  permanganate 
solution  is  decolorized  only  after  some  time  by  phosphites,  but  imme- 
diately by  hypophosphites. 

Phosphites  are  of  very  little  importance. 

Phosphoric  acids.  Phosphoric  oxide  is  capable  of  combining 
chemically  with  one,  two,  or  three  molecules  of  water,  forming 
thereby  three  different  acids. 

P2O5  +     H2O  =  H2P2O6  =  2HPO3   Metaphosphoric  acid. 
P2O5  -f  2H/)  =  H4P2O7  Pyrophosphoric  acid. 

P2O5  +  3H2O  =  H6P2O8  =  2H3PO4  Orthophosphoric  acid. 
15 


226  NON-METALS  AND   THEIR   COMBINATIONS. 

These  three  acids  show  different  reactions,  act  differently  upon  the 
animal  system,  and  form  different  salts. 

Metaphosphoric  acid,  HPO3,  PO2OH  (Glacial  phosphoric,  acid). 
This  acid  is  always  formed  when  phosphoric  oxide  is  dissolved  in 
water ;  gradually,  and  more  rapidly  on  heating  with  water,  it  absorbs 
the  latter,  forming  orthophosphoric  acid;  by  heating  the  latter  to 
near  a  red  heat  metaphosphoric  acid  is  re-formed. 

Metaphosphoric  acid  is  a  monobasic  acid  which  forms  colorless, 
transparent,  amorphous  masses,  readily  soluble  in  water.  It  coagu- 
lates albumin  (pyro-  and  orthophosphoric  acids  do  not)  and  gives  a 
white  precipitate  with  ammonio-silver  nitrate ;  it  is  not  precipitated 
by  magnesium  sulphate  in  the  presence  of  ammonia  and  ammonium 
chloride.  It  acts  as  a  poison,  while  common  phosphoric  acid  is 
comparatively  harmless. 

Pyrophosphoric  acid,  H4P2O7,  P2O3(OH)4.  This  is  a  tetra-basic  acid 
which  gives  a  white  precipitate  with  ammonio-silver  nitrate,  while  orthophos- 
phoric acid  gives  a  yellowish  precipitate ;  it  is  not  precipitated  by  ammonium 
molybdate,  and  does  not  coagulate  albumin. 

Phosphoric  acid,  Orthophosphoric  acid,  Acidum  phosphoricum, 
H3PO4,  PO(OH)3  =  97.29  (Common  or  tribasic  phosphoric  acid). 
Nearly  all  phosphates  found  in  nature  are  orthophosphates. 

Phosphoric  acid  may  be  made  by  burning  phosphorus,  dissolving 
the  phosphoric  oxide  in  water,  and  boiling  for  a  sufficient  length  of 
time  to  convert  the  meta-  into  orthophosphoric  acid. 

Experiment  16.  Place  a  piece  of  phosphorus  (about  0.5  gramme),  after  having 
dried  it  quickly  between  filter  paper,  in  a  small  porcelain  dish,  standing  upon 
a  glass  plate ;  ignite  the  phosphorus  by  touching  it  with  a  heated  wire,  and 
place  over  the  dish  an  inverted  large  beaker.  The  white  vapors  of  phosphoric 
oxide  soon  condense  into  flakes,  which  fall  on  the  glass  plate.  Collect  the 
white  mass  with  a  glass  rod,  'and  dissolve  in  a  few  c.c.  of  water.  Use  a  portion 
of  the  solution  for  tests  of  metaphosphoric  acid;  evaporate  the  remaining 
quantity  in  a  porcelain  dish  until  it  becomes  syrupy,  dilute  with  water  and  use 
it  for  making  tests  for  orthophosphoric  acid,  either  as  such  or  after  having 
neutralized  with  sodium  carbonate.  How  much  phosphorus  is  needed  to  make 
490  grammes  of  the  U.S. P.  10  per  cent,  phosphoric  acid? 

Phosphoric  acid  is  also  made  by  gently  heating  pieces  of  phos- 
phorus with  diluted  nitric  acid,  when  the  phosphorus  is  oxidized, 
red  fumes  of  nitrogen  tetroxide  escaping  : 

3P  +  5HNO3  +  2H2O  =  3H3PO4  +  5NO. 

The  liquid  is  evaporated  until  the  excess  of  nitric  acid  has  been 


PHOSPHORUS.  227 

expelled,  and  enough  of  water  added  to  obtain  an  acid  which  contains 
85  per  cent,  of  the  pure  H3PO4.  Specific  gravity  1.707  at  25°  C. 

Diluted  phosphoric  acid,  U.  S.  P.,  is  made  by  mixing  100  Gm.  of 
the  85  per  cent,  acid  with  750  Gm.  of  water.  It  contains  10  per  cent, 
of  absolute  orthophosphoric  acid. 

Phosphoric  acid,  U.  S.  P.,  is  a  colorless,  odorless,  strongly  acid 
liquid,  which,  on  evaporation,  forms  a  thick  syrupy  liquid.  This,  on 
cooling,  slowly  solidifies  in  the  form  of  large  crystals,  which  are 
highly  deliquescent.  Heated  to  a  sufficiently  high  temperature  the 
acid  loses  water,  being  converted  successively  into  pyrophosphoric 
and  metaphosphoric  acid,  which  is  finally  volatilized  at  a  low  red 
heat.  It  is  a  tribasic  acid,  forming  three  series  of  salts,  namely  : 

Na3PO4  =  Trisodium  phosphate. 

Na2HPO4        =  Disodium  hydrogen  phosphate. 
NaH2PO4         =  Sodium  dihydrogen  phosphate. 

If  the  metal  be  bivalent,  the  formulas  are  thus  : 

Ca3(PO4)2         =  Tricalcium  phosphate. 
Ca2H2(PO4)2    =  Dicalcium  orthophosphate. 
CaH4(PO4)2     =  Monocalcium  orthophosphate. 

According  to  the  number  of  hydrogen  atoms  replaced  in  the  acid, 
the  salts  formed  are  also  termed  primary,  secondary,  and  tertiary 
phosphates ;  KH2PO4  being,  for  instance,  primary  potassium  phos- 
phate ;  Na2HPO4  secondary  sodium  phosphate ;  Ag3PO4  tertiary  sil- 
ver phosphate.  All  the  alkali  phosphates,  but  only  primary  phos- 
phates of  the  other  metals,  are  soluble  in  water. 

All  phosphates  insoluble  in  water  are  dissolved  by  nitric,  hydrochloric,  or 
sulphuric  acid ;  also  by  acetic  acid,  except  those  of  lead,  aluminum,  and  ferric 
iron.  All  are  soluble  in  phosphoric  acid  (forming  acid  phosphates),  except  those 
of  lead,  tin,  mercury,  and  bismuth.  Primary  alkali  phosphates  are  acid  to 
litmus,  but  secondary  alkali  phosphates,  although  they  are  acid  salts,  are  alka- 
line to  litmus  because  of  partial  hydrolysis  by  water  into  primary  phosphate  and 
free  alkali.  Tertiary  alkali  phosphates  are  decomposed  by  water  into  the  second- 
ary salt  and  free  alkali. 

Phosphoric  acid  belongs  to  the  class  of  weak  acids,  and  the  three  hydrogen 
atoms  in  the  molecule  show  very  different  degrees  of  dissociation.  It  dissoci- 
ates chiefly  according  to  this  equation,  H3PO4  ~£.  H*  +  H2PO/.  The  dihy- 
drophosphate  ion,  H2PO/,  dissociates  to  a  small  degree  into  H*  and  HPO/' 
ions,  as  is  shown  by  the  fact  that  monosodium  phosphate  has  a  slightly  acid 
reaction  to  litmus,  thus : 

NaH2PO4    ^    Na*     +     H2PO/ 
H2PO4'        ^1    H'      +    HP04/X. 

The  ion  HPO/'  is  practically  not  dissociated  into  H'  and  PO/'  ions,  as  is 


228  NON-METALS  AND   THEIR  COMBINATIONS. 

evidenced  by  the  slightly  alkaline  reaction  of  disodium  phosphate,  which  dis- 
sociates thus, 

Na2HP04    i±    2Na-     +     HPO4". 

The  alkaline  reaction  is  due  to  the  formation  of  a  slight  quantity  of  free  alkali 
by  the  ions  of  water  (hydrolysis)  thus, 

2Na«      +   HPO/'l^  Hjpo, 
(OH)'   +   H-         / 

Na2HPO4    +     H20    =     NaOH     +    NaH2PO4, 

Trisodium  phosphate  is  completely  hydrolyzed  in  solution  into  disodium  phos- 
phate and  sodium  hydroxide,  Na3PO4  +  H2O  =  Na2HPO4  +  NaOH. 

Tests  for  phosphoric  acid  and  phosphates. 
(Sodium  phosphate,  Na^HPO^  may  be  used.) 

1.  Add  to  phosphoric  acid,  or  to  an  aqueous  solution  of  a  phos- 
phate, a  mixture  of  magnesium  sulphate,  ammonium  chloride,  and 
ammonia  water ;  a  white  crystalline  precipitate  falls,  which  is  mag- 
nesium ammonium  phosphate : 

H3P04  +  MgS04  +  3NH4OH  =  MgNH4PO4  +  (NH4)2SO4  +  3H2O; 
Na-jHPO,  -f  MgS04  +  NH4OH  =  MgNH4PO4  +  Na£O4  +  H2O. 

2.  Add  to  a  solution  of  disodium  phosphate,  silver  nitrate  ;  a  yellow 
precipitate  of  silver  phosphate  is  produced,  which  is  soluble  both  in 
ammonia  and  nitric  acid  : 

Na,HP04  +  3AgN03  =  Ag3PO4  +  2NaNO3  +  HN03. 

3.  Add  to  phosphoric  acid,  or  to  a  phosphate  dissolved  in  water 
or  in  nitric  acid,  an  excess  of  a  solution  of  ammonium  molybdate  in 
dilute  nitric  acid,  and  heat  gently ;  a  yellow  precipitate  of  phospho- 
molybdate  of  ammonium,  (NH4)3PO4.10MoO3.2H2O,  is  produced ; 
the  precipitate  is  readily  soluble  in  ammonia  water.     This  test  is  by 
far  the  most  delicate,  and  even  traces  of  phosphoric  acid  may  be 
recognized  by  it ;  moreover,  it  can  be  used  in  an  acid  solution,  while 
the  first  two  tests  cannot.     Only  a  few  drops  of  the  solution  to  be 
tested  should  be  used. 

4.  Add  to  a  solution  of  a  phosphate,  calcium  or  barium   chloride ; 
a  white  precipitate  of  calcium  or  barium  phosphate  is  produced,  which 
is  soluble  in  acids. 

5.  Ferric  chloride  produces  a  yellowish-white  precipitate  of  ferric 
phosphate,  Fe2(PO4)2,  thus : 

2Na,HP04  +  Fe.Cle  =  Fe2(PO4)2  +  4NaCl  +  2HC1. 
The  liberated  hydrochloric  acid  dissolves  some  of  the  precipitate, 
which  may  be  avoided  by  adding  previously  some  sodium  acetate ; 


PHOSPHORUS.  229 

the  hydrochloric  acid  combines  with  the  sodium  of  the  acetate,  and 
the  acetic  acid  which  is  set  free  has  no  dissolving  action  upon  the 
ferric  phosphate. 

Hydrogen  phosphide,  PH3  (Phosphoretted  hydrogen, phosphine).  The  forma- 
tion of  this  compound  has  been  mentioned  in  the  paragraph  on  Hypophos- 
phorous  acid.  It  is  a  colorless,  badly  smelling,  poisonous  gas,  which,  when 
generated  as  directed  above,  is  .spontaneously  inflammable.  This  last-named 
property  is  due  to  the  presence  of  small  quantities  of  another  compound  of 
phosphorus  and  hydrogen  which  has  the  composition  P2H4,  and  is  spontaneously 
inflammable,  while  the  compound  PH3  is  not. 

Hydrogen  phosphide  corresponds  to  the  analogous  composition  of  ammonia, 
NH3.  While  the  latter  is  readily  soluble  in  water  and  has  strong  basic  prop- 
erties, hydrogen  phosphide  is  but  sparingly  soluble  in  water  and  its  basic  prop- 
erties are  very  weak.  However,  a  few  salts,  such  as  the  phosphonium  chloride, 
PH4C1,  analogous  to  ammonium  chloride,  NH4C1,  are  known. 

There  is  no  scientific  evidence  whatever  for  the  correctness  of  the  statement, 
found  in  some  text-books,  that  hydrogen  phosphide  is  a  product  of  the  putre- 
faction of  certain  organic  compounds. 

Phosphorus  trichloride,  PC13.  This  is  a  colorless  liquid,  heavier  than 
water,  boiling  at  76°  C.  Its  vapors  are  very  pungent.  Water  decomposes  it 
very  rapidly  into  phosphorous  and  hydrochloric  acids,  thus,  PC13  -f-  3H2O  = 
HsP03  +  3HC1.  For  this  reason  the  liquid  gives  white  fumes  in  moist  air. 
It  can  only  be  obtained  by  direct  union  of  the  elements.  This  is  done  by 
leading  chlorine  gas  over  phosphorus  in  a  retort,  when  the  elements  unite  with 
combustion,  and  the  trichloride  distils  over  into  a  cold  receiver.  It  is  purified 
by  redistillation  in  contact  with  some  phosphorus,  which  removes  any  penta- 
chloride  present. 

Phosphorus  pentachloride,  PC15.  This  consists  of  pale  yellow  crystals, 
and  is  obtained  by  passing  chlorine  into  phosphorus  trichloride.  It  decom- 
poses at  once  in  water  into  phosphoric  and  hydrochloric  acids,  PC15  +  4H2O  — 
H3PO4  -f  5HC1.  It  fumes  strongly  in  moist  air.  At  300°  C.  it  is  completely 
dissociated  into  trichloride  and  chlorine.  With  a  small  proportion  of  water  it 
forms  phosphorus  oxychloride  thus,  PC15  +  H2O  =  POC13  +  2HC1.  The  oxy- 
chloride  is  a  colorless  liquid  that  boils  at  107.2°  C.  The  pentachloride  is  often 
used  in  organic  chemistry  to  substitute  chlorine  for  hydroxyl  (OH)  in  compounds. 

The  bromine  compounds  of  phosphorus,  PBr3  and  PBr5,  are  very  similar  to 
the  chlorine  compounds,  and  are  made  in  the  same  way. 

QUESTIONS.— In  what  forms  of  combination  is  phosphorus  found  in  na- 
ture? Give  an  outline  of  the  process  for  manufacturing  phosphorus.  What 
are  the  symbol,  valence,  atomic,  and  molecular  weights  of  phosphorus.  State 
the  chemical  and  physical  properties  both  of  common  and  red  phosphorus. 
By  what  methods  may  phosphorus  be  detected  in  cases  of  poisoning?  What 
two  oxides  of  phosphorus  are  known ;  what  is  their  composition,  and  what 
four  acids  do  they  form  by  combining  with  water?  State  the  official  process 
for  making  phosphoric  acid,  and  what  are  its  properties?  By  what  tests  may 
the  three  phosphoric  acids  be  recognized  and  distinguished  from  phosphorous 
acid?  What  is  a  phosphide,  phosphite,  phosphate,  and  hypophosphite ? 
What  is  glacial  phosphoric  acid,  and  in  what  respect  does  its  action  upon  the 
animal  system  differ  from  the  action  of  common  phosphoric  acid? 


230  NON-METALS  AND  THEIR  COMBINATIONS. 

18.  CHLOEINE. 

Cl'  =  35  (35.18). 

Halogens.  The  four  elements,  fluorine,  chlorine,  bromine,  and 
iodine,  which  form  a  natural  group  of  elements,  are  known  as  halogens, 
the  term  meaning  producers  of  salt.  The  relation  shown  by  the  atomic 
weights  of  these  four  elements  has  been  mentioned  in  connection  with 
the  consideration  of  natural  groups  of  elements  generally  (see  page 
125).  In  many  other  respects  a  resemblance  or  relation  can  be  dis- 
covered. For  instance- :  While  the  haloids  as  a  general  rule  act  as 
univalent  elements,  they  all  form  compounds  into  which  they  enter 
with  a  valence  of  either  3,  5,  or  7 ;  they  combine  with  hydrogen, 
forming  the  acids  HF,  HC1,  HBr,  HI,  all  of  which  are  colorless 
gases,  soluble  in  water ;  they  combine  directly  with  most  metals, 
forming  fluorides,  chlorides,  bromides,  and  iodides.  The  relative 
combining  energy  lessens  as  the  atomic  weight  increases  ;  fluorine 
with  the  lowest  atomic  weight  having  the  greatest,  iodine  with  the 
highest  atomic  weight  the  smallest,  affinity  for  other  elements.  The 
first  two  members  of  the  group  are  gases,  the  third  (bromine)  is  a 
liquid,  the  last  (iodine)  a  solid,  at  ordinary  temperature.  They  all 
show  a  distinct  color  in  the  gaseous  state,  have  a  disagreeable  odor, 
and  possess  disinfecting  properties. 

Occurrence  in  nature.  Chlorine  is  found  chiefly  as  sodium 
chloride  or  common  salt,  NaCI,  either  dissolved  in  water  (small 
quantities  in  almost  every  spring  water,  larger  quantities  in  some 
mineral  waters,  and  the  principal  amount  in  sea-water),  or  as  solid 
deposits  in  the  interior  of  the  earth  as  rock  salt. 

Other  chlorides,  such  as  those  of  potassium,  magnesium,  calcium, 
also  are  found  in  nature.  As  common  salt,  chlorine  enters  the  animal 
system,  taking  there  an  active  part  in  many  of  the  physiological  and 
chemical  changes. 

Preparation  of  chlorine.  Most  methods  of  liberating  chlorine 
depend  on  an  oxidation  of  the  hydrogen  of  hydrochloric  acid  by 
suitable  oxidizing  agents,  the  hydrogen  being  converted  into  water, 
while  chlorine  is  set  free. 

As  oxidizing  agents,  may  be  used  potassium  chlorate,  potassium 
dichromate,  potassium  permanganate,  chromic  acid,  nitric  acid,  and 
many  other  substances. 

The  most  common  and  cheapest  mode  of  obtaining  chlorine  is  to 
heat  manganese  dioxide,  usually  called  black  oxide  of  manganese, 


CHLORINE.  231 

with   hydrochloric   acid,  or  a  mixture  of  manganese   dioxide   and 
sodium  chloride  with  sulphuric  acid : 

Mn02  +  4HC1  =  MnCl2  -f  2H2O  +  2C1. 

MnO2  +  2NaCl  -f  2H2SO4  =  MnSO4  -f  Na2SO4  -f  2H2O  +  2C1. 
Chlorine  is  liberated  also  by  the  action  of  sulphuric  or  hydrochloric  acid  on 
bleaching-powder,  which  is  a  mixture  of  calcium  chloride  and  calcium  hypo- 
chlorite : 

CaCl2.Ca(ClO)2   -f   2H2SO4   =   2CaSO4   +   2H2O   +   401. 

Chlorine  is  now  also  produced  by  electrolysis  of  sodium  chloride  solution  in 
suitably  constructed  apparatus. 

Experiment  17.  Use  apparatus  as  in  Fig.  39,  page  168.  Conduct  operation 
in  a  fume-chamber.  Place  about  50  grammes  of  manganese  dioxide  in  coarse 
powder  in  the  flask,  cover  it  with  hydrochloric  acid,  shake  up  well  to  insure 
that  no  dry  powder  be  left  at  the  bottom  of  the  flask,  apply  heat,  and  collect 
the  gas  in  dry  bottles  by  downward  displacement.  Keep  the  bottles  loosely 
covered  with  pieces  of  stiff  paper  while  filling  them.  Use  the  gas  for  the 
following  experiments : 

a.  Fill  a  test-tube  with  chlorine,  a  second  test-tube  of  same  size  with  hydro- 
gen ;  place  them  over  one  another  so  that  the  gases  mix  by  diffusion,  then 
hold  them  near  a  flame ;  a  rapid  combustion  or  explosion  ensues. 

b.  Hold  in  one  of  the  bottles  filled  with  chlorine  a  lighted  wax  candle,  and 
notice  that  it  continues  to  burn  with  liberation  of  carbon.    The  hydrogen  con- 
tained in  the  wax  is  in  this  case  the  only  constituent  of  the  wax  which  burns, 
i.  e.,  combines  with  chlorine. 

c.  Moisten  a  paper  with  oil  of  turpentine,  C10H16,  and  drop  it  into  another 
bottle  filled  with  the  gas ;  combustion  ensues  spontaneously,  a  black  smoke  of 
carbon  being  liberated. 

d.  Drop  some  finely  powdered  antimony  into  another  bottle,  and  notice  that 
each  particle  of  the  metal  burns  while  passing  through  the  gas,  forming  white 
antimonous  chloride,  SbCls. 

e.  Pass  some  chlorine  gas  into  water,  and  suspend  in  the  chlorine  water  thus 
formed  colored  flowers  or  pieces  of  dyed  cotton,  and  notice  that  the  color  fades 
and  in  many  cases  disappears  completely  in  a  few  hours. 

Properties.  Chlorine  is  a  yellowish-green  gas,  having  a  disagree- 
able taste  and  an  extremely  penetrating,  suffocating  odor,  acting 
energetically  upon  the  air-passages,  producing  violent  coughing  and 
inflammation.  It  is  about  two  and  a  half  times  heavier  than  air, 
soluble  in  water,  and  convertible  into  a  greenish-yellow  liquid  by  a 
pressure  of  about  six  atmospheres. 

Chemically,  the  properties  of  chlorine  are  well  marked,  and  there 
are  but  few  elements  which  have  as  strong  an  affinity  for  other  ele- 
ments as  chlorine ;  it  unites  with  all  of  them  directly,  except  with 
oxygen,  nitrogen,  and  carbon,  but  even  with  these  it  may  be  made  to 
combine  indirectly.  The  act  of  combination  between  chlorine  and 
other  elements  is  frequently  attended  by  the  evolution  of  so  much 


232  NON-METALS  AND  THEIR  COMBINATIONS. 

heat  that  light  is  produced,  or,  in  other  words,  combustion  takes  place. 
Thus,  hydrogen,  phosphorus,  and  many  metals  burn  easily  in  chlorine. 
The  affinity  between  chlorine  and  hydrogen  is  intense,  a  mixture  of 
the  two  gases  being  highly  explosive.  Such  a  mixture,  kept  in  the 
dark,  will  not  undergo  chemical  change,  but  when  ignited,  or  when 
exposed  to  direct  sunlight,  combination  between  the  two  elements 
occurs  instantly  with  an  explosion.  The  affinity  of  chlorine  for 
hydrogen  is  also  demonstrated  by  its  property  of  decomposing  water, 
ammonia,  and  many  hydrocarbons  (compounds  of  carbon  with  hydro- 
gen), such  as  oil  of  turpentine,  C10H16,  and  others  : 

H20  +     2C1  =    2HC1  -f      O. 

NH3     +    3C1  =    3HC1  +      N. 

C10H16    +  16C1  =  16HC1  +  IOC. 

As  shown  by  these  formulas,  hydrochloric  acid  is  formed,  while 
the  other  elements  are  set  free. 

Chlorine  is  a  strong  disinfecting,  deodorizing,  and  bleaching  agent  ; 
it  acts  as  such  either  directly  by  combining  with  certain  elements  of 
the  coloring  or  odoriferous  matter,  or,  indirectly,  by  decomposing 
water  with  liberation  of  oxygen,  which  in  the  nascent  state  —  that  is, 
at  the  moment  of  liberation—  has  a  strong  tendency  to  oxidize  other 
substances. 

It  should  be  noted  that  perfectly  dry  chlorine  has  practically  no  action  on 
other  substances  when  also  dried.  In  the  absence  of  all  moisture  it  has  no 
bleaching  action.  This  inactivity  of  dry  chlorine  is  exemplified  by  the  fact  that 
it  is  now  sold  in  steel  cylinders.  As  ordinarily  used,  however,  it  acts  readily, 
because  of  the  moisture  in  the  atmosphere,  and  on  objects,  even  if  water  is  not 
supplied  directly. 

Compound  solution  of  chlorine,  Liquor  chlori  compositus  (Chlorine 
water).  Cold  water  absorbs  about  two  volumes  of  chlorine,  which  is  equal  to 
0.4  per  cent,  by  weight.  This  solution  is  unstable  because  the  chlorine  grad- 
ually combines  with  hydrogen  of  water,  while  oxygen  is  set  free.  It  is  for  this 
reason  that  the  U.  S.  P.  has  substituted  for  ordinary  chlorine  water  the  com- 
pound solution  of  chlorine,  which  is  to  be  freshly  made  when  wanted.  It  is 
prepared  by  digesting  in  a  large  flask  potassium  chlorate  with  hydrochloric 
acid  and  then  adding  water  to  dissolve  the  liberated  chlorine,  as  also  some 
chlorinated  products  and  the  potassium  chloride  which  are  formed.  The 
reaction,  when  complete,  is  this  : 

KC103  +   6HC1  ==  KC1  +   3H2O   +   6C1. 
Chlorine  water  is  a  greenish-yellow  liquid,  having  the   odor  of  chlorine. 


Hydrochloric    acid,    Acidum    hydrochloricum,    ifCl  =  36.18 
(Muriatic  acid).     This  acid  occurs  in  the  gastric  juice  of  mammalia, 


CHLORINE.  233 

and  has  been  found  in  some  volcanic  gases.  One  volume  of  hydrogen 
combines  with  one  volume  of  chlorine  to  form  two  volumes  of  hydro- 
chloric acid. 

For  all  practical  purposes  the  acid  is  obtained  by  the  decomposition 
of  a  chloride  by  sulphuric  acid  : 

NaCl  +  H2S04  =    HC1  +  NaHSO4; 
or 

2NaCl  +  H2S04  =  2HC1 


Experiment  18.  Use  apparatus  as  in  Fig.  39,  p.  168.  Place  about  20  grammes 
of  sodium  chloride  into  the  flask  (which  should  be  provided  with  a  funnel-tube) 
and  add  about  30  c.c.  of  concentrated  sulphuric  acid  ;  mix  well,  apply  heat,  and 
pass  the  gas  into  water  for  absorption.  If  a  pure  acid  be  desired,  the  gas  has 
to  be  passed  through  water  contained  in  a  wash-bottle  ;  apparatus  shown  in 
Fig.  42,  page  207,  may  then  be  used.  Use  the  acid  made  for  tests  mentioned 
below.  How  much  of  the  U.  S.  P.  31.9  per  cent,  hydrochloric  acid  can  be 
made  from  117  pounds  of  sodium  chloride? 

The  liberation  of  hydrochloric  acid  from  a  chloride  by  sulphuric  acid  is  an 
example  of  reversible  reactions  that  run  to  completion  because  of  the  removal 
of  one  of  the  factors  that  is  necessary  to  maintain  an  equilibrium  (see  page 
114).  The  character  of  the  reaction  is  like  that  in  the  case  of  the  liberation 
of  nitric  acid,  the  ionic  features  of  which  are  discussed  in  Chapter  15.  The 
ionic  reaction  is  this  : 


NaCl    ^±  Na*       +  C1M    ^±  HC1  —  HC1. 
H2SO4  ^±  HSO/  +  H-  /     dissolved     gas. 


Hydrochloric  acid  is  a  colorless  gas,  has  a  sharp,  penetrating  odor, 
and  is  very  irritating  when  inhaled.  It  is  neither  combustible  nor 
a  supporter  of  combustion,  and  has  great  affinity  for  water,  which 
property  is  the  cause  of  the  formation  of  white  clouds  whenever  the  gas 
comes  in  contact  with  the  vapors  of  water,  or  with  moist  air  ;  the  white 
clouds  being  formed  of  minute  particles  of  liquid  hydrochloric  acid. 

While  hydrochloric  acid  is  a  gas,  this  name  is  used  also  for  its 
solution  in  water,  one  volume  of  which  at  ordinary  temperature  takes 
up  over  400  volumes  of  the  gas. 

The  hydrochloric  acid  of  the  U.  S.  P.  is  an  acid  containing  31.9 
per  cent,  of  HC1.  It  is  a  colorless,  fuming  liquid,  having  the  odor 
of  the  gas,  strong  acid  properties,  and  a  specific  gravity  of  1.158. 
The  official  diluted  hydrochloric  acid  is  made  by  mixing  100  parts 
by  weight  of  the  above  acid  with  219  parts  of  water.  It  contains  10 
per  cent,  of  HCL 

The  same  antidotes  may  be  used  as  for  nitric  acid. 

A  20.2  per  cent,  solution  of  hydrochloric  acid  distils  unchanged  at  110°  C. 
(230°  F.)  under  760  mm.  pressure.  When  a  more  concentrated  solution  is 
heated,,  it  first  loses  mainly  the  gas,  and  a  more  dilute  solution  mainly  water 


234  NON-METALS  AND   THEIR   COMBINATIONS. 

vapor,  until  20.2  per  cent,  is  reached,  when  the  residue  in  the  flask  passes  over 
unchanged.  Other  acids— for  example,  sulphuric,  nitric,  hydriodic,  hydro- 
brornic — show  a  similar  property. 

Neither  the  dry  gas  (HC1)  nor  the  liquefied  gas  has  any  marked  acid  char- 
acter. They  do  not  conduct  electricity  and  have  no  action  on  dry  litmus- 
paper  or  on  zinc,  but  the  presence  of  water  causes  strong  acid  properties  to  be 
developed.  This  is  explained  on  the  Dissociation  Theory,  which  holds  that 
only  hydrogen  ions  have  acid  properties.  Water  is  required  for  the  ionization 
of  HC1,  and  without  it  the  gas  lacks  acid  character.  A  solution  of  the  gas  in 
liquids  like  benzene  and  toluene,  which  have  scarcely  any  ionizing  power,  has 
practically  no  effect  on  zinc,  which  is  freely  attacked  by  an  aqueous  solution 
of  the  gas.  The  same  is  true  of  hydrobromic  and  hydriodic  acids  (Chapter 
15). 

Nearly  all  chlorides  are  soluble  in  water.  Of  those  ordinarily  met  with 
only  two  are  insoluble  in  water,  namely,  silver  and  mercurous  chlorides,  and 
one  is  difficultly  soluble  in  cold  water,  but  more  readily  in  hot  water,  namely, 
lead  chloride. 

Tests  for  hydrochloric  acid  and  chlorides. 
(Sodium  chloride,  NaCl,  may  be  used.) 

1.  To  hydrochloric  acid,  or  to  solution  of   chlorides,  add   silver 
nitrate :  a  white,  curdy  precipitate  is  produced,  which  is  soluble  in 
ammonia  water,  even  when  very  dilute,  but  insoluble  in  nitric  acid : 

AgN03    +    Nad    =    AgCl.     -f     NaNO3. 
Ag'     +     NO/    +    Na'     +     Cl'    —     AgCl     '+     Na'     +     NO/. 

2.  Add  solution  of  mercurous  salt  (mercurous   nitrate) :   a  white 
precipitate  of  mercurous  chloride  (calomel)  is  produced,  which  black- 
ens on  the  addition  of  ammonia  : 

HgN03     +     NaCl    =    HgCl     +     NaNO3. 
Hg'    +    N03'    +    Na-     +     Cl'   —    HgCl     +     JNV     +     NO/. 

3.  Add  solution  of  lead  acetate  :  a  white  precipitate  of  lead  chloride 
is  formed,  which  is  soluble  in  hot,  or  in  much  cold  water,  and  is,  there- 
fore, not  formed  in  dilute  solutions.     Its  composition  is  PbCl2. 

Pb(C2H302)2     +     2NaCl  PbCl2     +     2Na(C2H3O2). 

Pb"    +    2(C,H302)'   +    2Na-     +    201'  -  PbCl2    +    2Na'    +    2(C2H3O2)'. 

4.  To  a  dry  chloride  add  strong  sulphuric  acid  and  heat :  hydro- 
chloric acid  gas  is  evolved,  which  may  be  recognized  by  the  odor,  or 
by  its  action  on  silver  nitrate,  when  a  drop  of  the  solution  on  the  end 
of  a  glass  rod  is  held  in  the  gas.     (The  insoluble  chlorides  of  silver, 
lead,  and  mercury  do  not  give  this  reaction.) 

5.  Chlorides  treated  with  sulphuric  acid  and  manganese  dioxide 
evolve  chlorine. 

Test  1,  combined  with  test  5,  is  the  most  decisive  proof  of  hydro- 


CHLORINE.  235 

chloric  acid  or  chlorides.     The  others  are  more  corroborative  than 
decisive. 

Nitro-hydrochloric  acid,  Acidum  nitro-hydrochloricum,  Aqua 
regla  (Nitro-muriatic  acid).  Obtained  by  mixing  18  c.c.  of  nitric 
acid  with  82  c.c.  of  hydrochloric  acid.  The  two  acids  act  chemically 
upon  each  other,  forming  chloronitrous  gas,  chlorine,  and  water : 

HN03  +  3HC1  =  NOC1  +  2H2O  +  2C1. 

The  dissolving  power  of  this  acid  upon  gold  and  platinum  depends 
on  the  action  of  the  free  chlorine.  The  action  on  platinum  is  repre- 
sented by  this  equation  : 

2HNO3  +  8HC1  +  Pt  =  H2Pt.Cl6  f  2NOC1  -f  4H2O. 

Chloroplatinic  acid,  H2PtCl6,  is  in  solution.     This  is  used  as  a  test- 
solution. 

The  official  diluted  nitrohydrochloric  acid  is  made  by  mixing  182  c.c.  of  hydro- 
chloric acid  with  40  c.c.  of  nitric  acid  and  adding,  when  effervescence  has 
ceased,  782  c.c.  of  water. 

Compounds  of  chlorine  -with  oxygen.  There  is  no  method  known 
by  which  to  combine  chlorine  and  oxygen  directly,  all  the  compounds  formed 
by  the  union  of  these  ele%ients  being  obtained  by  indirect  processes.  The 
oxides  of  chlorine  are  the  following: 

Chlorine  monoxide  or  hypochlorous  oxide,     C12O. 
Chlorine  dioxide,  C1Q2. 

Chlorine  heptoxide,  C12O7. 

The  first  two  oxides  are  yellow  or  brownish-yellow  gases ;  the  third  one  is  a 
colorless  liquid ;  all  combine  with  water,  forming  hypochlorous,  chlorous  and 
chloric,  and  perchloric  acid,  thus : 

C12O       +     H2O     =     2HC1O. 

2C102     +    H20  HC102    +    HC103. 

C12O7      +    H2O  2HC104. 

The  oxide,  C12O5,  from  which  chloric  acid,  HC1O3,  might  be  formed,  is  not 
known.  The  chlorine  oxides,  the  acids,  and  many  of  their  salts  are  distin- 
guished by  the  great  facility  with  which  they  decompose,  frequently  with  vio- 
lent explosion,  for  which  reason  care  must  be  taken  in  the  preparation  and 
handling  of  these  compounds. 

Chlorine  acids. 

Hypochlorous  acid,      HC1O.  Chloric  acid,  HC1O8. 

Chlorous  acid,  HC1O2.  Perchloric  acid,  HC1O4. 

Hydrochloric  acid,         HC1. 


236  NON-METALS  AND   THEIR  COMBINATIONS. 

With  the  exception  of  hydrochloric  acid,  which  has  been  considered, 
none  of  the  five  acids  is  of  practical  interest  as  such,  but  many  of 
the  salts  of  hypochlorous  and  chloric  acids,  known  as  hypochlorites 
and  chlorates  respectively,  are  of  great  and  general  importance. 

The  constitution  of  the  chlorine  acids  may  be  represented  by  the  following 
graphic  formulas.  It  is  here  assumed  that  chlorine  is  univalent  in  hypochlo- 
rous, trivalent  in  chlorous,  quinquivalent  in  chloric,  and  septivalent  in  per- 
chloric acid : 

II  II 

H  — O  — Cl,    H  — O  — Cl  =  0,     H  — O  — Cl,    H  —  O  —  Cl  =  O 

O  O 

Chlorine  monoxide,  C12O,  and  Hypochlorous  acid,  HC1O.  When 
chlorine  is  passed  over  yellow  mercuric  oxide  in  a  tube,  chlorine  mon- 
oxide is  formed,  thus, 

2HgO  +  2C12  =  HgO.HgCL,  +  C12O. 

It  is  a  brownish-yellow  gas  which  decomposes  with  explosion  when 
heated.  One  volume  of  water  dissolves  200  volumes  of  the  gas, 
giving  a  yellow  solution  of  hypochlorous  acid  which  has  the  strong 
odor  of  the  chlorine  monoxide, 

C12O  +  H2O  =  2HC1O. 

Hypochlorous  acid  is  also  obtained  in  solution  when  chlorine  gas  is 
passed  into  a  suspension  of  mercuric  oxide  in  water,  thus, 

2HgO  +  2C12  +  H20  =  HgO.HgCl,  -f  2HC1O. 

The  compound  known  as  mercury  oxychloride  is  formed  and  may  be 
removed,  being  insoluble. 

Properties.  Hypochlorous  acid  is  a  feeble  (slightly  ionizing)  mono- 
basic acid,  which  unites  with  active  bases,  forming  hypochlorites.  It 
can  be  obtained  only  in  solution,  and  keeps  only  when  dilute  and 
cold.  When  concentrated  it  changes  gradually  to  a  considerable  ex- 
tent into  chloric  and  hydrochloric  acids,  thus, 
3HC10  =  HC103  +  2HC1. 

Warming  a  solution  of  the  acid,  or  exposing  it  to  sunlight,  causes  a 
rapid  evolution  of  oxygen, 

2HC10  =  2HC1  +  2O. 

As  a  result  of  this  action,  the  acid  is  a  strong  oxidizer.  This  decom- 
position is  interesting,  as  it  explains  the  oxidizing  action  of  chlorine 
in  the  presence  of  water,  and  the  fact  that  chlorine  water  exposed  to 
bright  light  does  not  keep,  but  gives  off  oxygen  and  leaves  a  solution 
of  nothing  but  hydrochloric  acid.  When  chlorine  is  dissolved,  a  re- 
versible reaction  takes  place,  thus, 

C12  +  H20  ^±  HC1  +  HC10. 


CHLORINE.  237 

Only  a  slight  quantity  of  hypochlorous  acid  is  formed  at  one  time, 
but  its  decomposition  and  constant  removal  in  this  way  allows  the 
action  to  go  forward  to  completion.  The  final  result  makes  it  appear 
that  chlorine  decomposes  water  with  direct  liberation  of  oxygen, 
which  is  usually  represented  by  the  equation, 

C12  +  H2O  =  2HC1  +  O. 

Hypochlorites.  For  practical  purposes  solutions  of  free  hypochlorous 
acid  are  not  made,  but  the  acid  is  liberated  from  its  salts  when  wanted.  The 
hypochlorites  are  formed  by  the  action  of  chlorine  on  the  hydroxide  of  potas- 
sium, sodium,  calcium,  etc.,  at  the  ordinary  temperature.  As  stated  above, 
chlorine  with  water  forms  HC1  and  HC1O,  but  the  action  does  not  go  far, 
because  these  two  acids  tend  to  decompose  each  other  in  the  reverse  direction 
to  produce  chlorine.  But  if  they  are  removed,  as  by  neutralization,  action 
will  be  complete,  thus, 

2C1      -f  H2O      =  HC1       +  HC1O 

HC1     +  NaOH  =  NaCl     +  H2O 

HC10  +  NaOH  =  NaCIO  +  H2O. 

It  will  be  seen  that  when  hypochlorite  is  made  in  this  manner  there  is  always 
an  equivalent  amount  of  a  chloride  in  the  mixture.  The  reaction  is  generally 
written, 

2C1  +  2NaOH  =  NaCl  +  NaCIO  +  H2O. 

When  a  hypochlorite  is  acidified  with  an  active  acid,  the  reverse  of  the  above 
reactions  takes  place,  hydrochloric  and  hypochlorous  acids  being  liberated, 
which  between  them  evolve  chlorine  (see  bleaching  powder).  When  a  hypo- 
chlorite is  heated,  it  decomposes  into  chlorate  and  chloride,  thus, 

SNaCIO  =  NaClOs  +  2NaCl. 

Under  some  conditions  a  hypochlorite  slowly  gives  off  oxygen,  leaving  a  chlo- 
ride, but  the  action  may  be  enormously  increased  by  adding  a  catalytic  agent, 
for  example,  a  cobalt  salt  (see  under  Oxygen). 

Solution  of  chlorinated  soda,  Liquor  sodae  chlorinatse  (Solution  of 
sodium  hypochlorite,  Labarraque 's  solution).  This  is  a  solution  that  yields  2.4 
per  cent,  of  available  chlorine.  It  contains  chloride  and  hypochlorite  of  sodium, 
and  is  made  by  adding  sodium  carbonate  to  a  solution  of  bleaching  powder 
(calcium  hypochlorite),  thus  precipitating  calcium  carbonate : 

CaCl2  -f  Ca(ClO)2  -f  2Na2CO3  =  2CaCO3  -f  2NaCl  +  2NaClO. 

It  is  a  clear  pale  greenish  liquid,  having  a  faint  chlorine-like  odor  and  strong 
bleaching  properties. 

Chloric  acid,  HC1O3,  may  be  obtained  from  potassium  chlorate  b}* 
the  action  of  hydrofluosilicic  acid ;  it  is,  however,  an  unstable  sub- 
stance which  will  decompose,  frequently  with  a  violent  explosion. 
Chlorates  are  generally  obtained  by  the  action  of  chlorine  on  alkali 
hydroxides  at  a  temperature  of  about  100°  C.  (212°  F.). 
6KOH  +  6C1  as  5KC1  +  KC103  +  3H2O. 


238  NON-METALS  AND  THEIR   COMBINATIONS. 

The  explanation  of  this  action  is  that  chlorine  first  forms  a  hypo- 
chlorite,  which,  as  stated  above,  decomposes  by  heating  into  chlorate 
and  chloride.     The  change  will  be  clearer  if  written  in  two  steps : 
6KOH  +  6C1  =  3KC1  -f  3KC1O  +  3H2O. 

3KC10  =  2KC1  +  KC103. 

In  recent  years  large  quantities  of  chlorates,  especially  potassium 
chlorate,  are  made  by  passing  an  electric  current,  under  proper  con- 
ditions, through  an  alkaline  solution  of  potassium  chloride. 

Perchloric  acid,  HC1O4.  This  is  a  colorless  liquid,  which,  in  the  pure 
state,  decomposes,  and  often  explodes  spontaneously  when  kept.  A  70 
per  cent,  aqueous  solution  is  stable.  Although  it  contains  more  oxygen  than 
the  other  acids  of  chlorine,  it  is  the  most  stable  one  of  all.  It  can  be  prepared 
by  distilling  a  mixture  of  potassium  perchlorate  and  concentrated  sulphuric 
acid  in  a  vacuum.  It  was  seen  in  the  chapter  on  oxygen  that  potassium  chlor- 
ate, when  heated,  gives  the  perchlorate,  chloride,  and  oxygen.  The  perchlor- 
ate, being  difficultly  soluble  in  water,  can  be  separated  easily  from  the  far  more 
soluble  chloride. 

Tests  for  chlorates  and  hypochlorites. 
(Potass,  chlorate,  KC1O3,  and  bleaching  powder,  Ca(ClO)2.CaCl2,  may  be  used.) 

1.  Chlorates  liberate  oxygen  when  heated  by  themselves. 

2.  Chlorates  liberate  chlorine  dioxide,  C1O2,  a  deep-yellow  explo- 
sive gas,  on  the  addition  of  strong  sulphuric  acid. 

2KC103    +    H2S04    =    K2S04    +     2HC1O3. 
3HC103    =    HC104    +     H20       +    2C102. 

This  test  should  be  made  only  on  a  quantity  about  the  size  of  a  pea. 

3.  Chlorates  deflagrate  when  sprinkled  on  red-hot  charcoal. 

4.  Hypochlorites  are  strong  bleaching  agents,  and  evolve  a  pecu- 
liarly smelling  gas  (chlorine)  on  the  addition  of  acid  (see  page  236). 

QUESTIONS. — State  the  names  and  general  physical  and  chemical  properties 
of  the  four  halogens.  How  is  chlorine  found  in  nature,  and  why  does  it  not 
occur  in  a  free  state?  State  the  general  principle  for  liberating  chlorine  from 
hydrochloric  acid,  and  explain  the  action  of  the  latter  on  manganese  dioxide. 
Mention  of  chlorine :  its  atomic  weight,  molecular  weight,  valence,  color,  odor, 
action  when  inhaled,  and  solubility  in  water.  How  does  chlorine  act  chemi- 
cally upon  metals,  hydrogen,  phosphorus,  water,  ammonia,  hydrocarbons,  and 
coloring  matters?  Mention  two  processes  for  making  hydrochloric  acid;  state 
its  composition,  properties,  and  tests  by  which  it  may  be  recognized.  What  is 
aqua  regia?  State  the  composition  of  hypochlorous  and  chloric  acids.  What 
is  the  difference  in  the  action  of  chlorine  upon  a  solution  of  potassium  hydrox- 
ide at  ordinary  temperature  and  at  the  boiling-point  ?  How  many  pounds  of 
manganese  dioxide,  and  how  many  of  hydrochloric  acid  gas  are  required  to 
liberate  142  pounds  of  chlorine  ? 


BROMINE—  IODINE-  FL  UORINE.  239 

19.  BROMINE—  IODINE—  FLUORINE. 

Bromine,  Bro'mum,  Br  =  79.36.  This  element  is  found  in  sea- 
water  and  many  mineral  waters,  chiefly  as  magnesium,  calcium,  and 
sodium  bromides,  which  compounds,  however,  represent  in  all  these 
waters  a  comparatively  small  percentage  of  the  total  quantity  of  the 
different  salts  present.  Most  of  these  salts  are  separated  from  the 
water  by  evaporation  and  crystallization,  and  the  remaining  mother- 
liquor,  containing  the  bromides,  is  treated  with  chlorine,  which  liber- 
ates bromine,  the  vapors  of  which  are  condensed  in  cooled  receivers  : 

MgBr2     -f     2C1    =    MgCl2     +     2Br. 

Bromine  is  at  common  temperature  a  heavy,  dark  reddish-brown 
liquid,  giving  off  yellowish-red  fumes  of  an  exceedingly  suffocating 
and  irritating  odor;  it  is  very  volatile,  freezes  at  about  —  24°  C. 
(  —  11°  F.),  and  has  a  specific  gravity  of  2.99;  it  is  soluble  in  33 
parts  of  water,  more  freely  in  alcohol,  abundantly  in  ether  and  bisul- 
phide of  carbon  ;  it  is  a  strong  disinfectant,  and  its  aqueous  solution 
is  also  a  bleaching  agent  ;  it  acts  as  a  corrosive  poison. 

Hydrobromic  acid,  Acldum  hydrobromicum,  HBr  =  8O.36. 
This  acid  cannot  well  be  obtained  by  the  action  of  concentrated  sul- 
phuric acid  upon  bromides,  since  the  hydrobromic  acid  first  formed 
becomes  readily  decomposed  with  formation  of  sulphur  dioxide  and 
free  bromine.  Thus  : 


2NaBr     +     H2SO4    =    2HBr     +     Na2SO4; 
2HBr      +    H2SO4    =    2Br        +    SO2  +  2H2O. 

If,  however,  dilute  sulphuric  acid  is  added  to  a  warm  solution  of 
potassium  bromide,  potassium  sulphate  is  formed,  a  portion  of  which 
crystallizes  on  cooling.  From  the  remaining  portion  of  the  salt,  the 
hydrobromic  acid  may  be  separated  by  distillation. 

Hydrobromic  acid  may  also  be  obtained  by  the  formation  of  bromide  of 
phosphorus,  PBr5  (the  two  elements  combine  directly),  and  its  decomposition 

by  water  : 

PBr5     +     4H20    =    5HBr     +     H3PO4. 

In  the  form  of  solution  this  acid  may  be  prepared  also  by  treating  bromine 
under  water  with  hydrogen  sulphide  until  the  brown  color  of  bromine  has 
entirely  disappeared.  The  reaction  is  as  follows  : 

lOBr  +  2H2S  +  4H20  =  lOHBr  +  H2SO,  +  S. 

The  liquid  is  filtered  from  the  sulphur  and  separated  from  the  sulphuric  acid 
by  distillation, 


240  NON-METALS  AND   THEIR   COMBINATIONS. 

Hydrobromic  acid  is,  like  hydrochloric  acid,  a  colorless  gas,  of 
strong  acid  properties,  easily  soluble  in  water. 

Diluted  hydrobromic  avid,  Acidum  hydrobromicum  dilutum,  is  a  solu- 
tion of  10  per  cent,  of  hydrobromic  acid  in  water.  It  is  a  colorless, 
odorless,  acid  liquid  of  the  specific  gravity  1.076. 

Hydrobromic  acid  acts  in  nearly  all  respects  like  hydrochloric.  It  is  less 
stable,  and  less  powerful  oxidizing  agents  will  liberate  the  bromine  than  are 
required  to  liberate  chlorine.  Nearly  all  bromides  are  soluble  in  water,  the 
insoluble  ones  being  those  of  silver,  mercury  (ous),  and  lead.  Bromides  are 
mostly  white. 

The  ionic  reactions  for  bromine  compounds  are  analogous  to  those  for  chlo- 
rine compounds. 

Hypobromous  acid,  HBrO ;  Bromic  acid,  HBrO3,  and  their 
salts,  the  hypobromites  and  bromates,  are  analogous  to  the  corre- 
sponding chlorine  compounds,  and  may  be  obtained  by  analogous 
processes.  Oxides  of  bromine  are  not  known. 

Tests  for  Bromides. 
(Potassium  bromide,  KBr,  may  be  used.) 

1.  Silver  nitrate  produces  in  solutions  of  bromides  a  slightly  yel- 
lowish-white precipitate  of  silver  bromide,  insoluble  in  nitric  acid, 
sparingly  soluble  in  ammonia  water. 

2.  Addition  of  chlorine  water,  or  heating  with  nitric  acid,  liberates 
bromine,  which  may  be  dissolved  by  shaking  with  carbon  disulphide. 
Excess  of  chlorine  oxidizes  bromine  to  colorless  bromic  acid.     Hence, 
it  must  be  added  cautiously,  else  a  small  quantity  of  bromine  will 
escape  detection.     The  test  is  a  delicate  one. 

3.  Mucilage  of  starch  added  to  the  liberated  bromine  is  colored 
yellow.     The  starch  may  be  held  in  the  vapor  on  the  end  of  a  rod. 

4.  A  solution   of  mercurous  nitrate,  or  of  lead  acetate  produces 
a  white  precipitate  of  mercurous  bromide,  or  lead  bromide,  both  of 
which  are  insoluble  in  water  and  dilute  acids. 

5.  Strong  sulphuric  acid  added  to  a  dry  bromide  liberates  hydro- 
bromic acid,  HBr,  a  portion  of  which  decomposes  with  liberation  of 
yellowish-red  vapors  of  bromine.     See  explanation  above. 

Tests  2  and  5  combined  with  test  1  are  decisive  and  sufficient  to 
recognize  hydrobromic  acid  and  its  salts,  and  to  distinguish  them 
from  chlorides. 

Iodine,  lodum,  I  =  125.90.  Iodine  is  found  in  nature  in  com- 
bination with  sodium  and  potassium,  in  some  spring  waters  and  in 


BE  OMINE-  IODINE— FL  UOIilNE.  241 

sea-water,  from  which  latter  it  is  taken  up  by  sea-plants  and  many 
aquatic  animals.  Iodine  is  derived  chiefly  from  the  ashes  of  sea- 
weeds known  as  kelp.  By  washing  these  ashes  with  water,  the  soluble 
constituents  are  dissolved,  the  larger  quantities  of  sodium  chloride, 
sodium  and  potassium  carbonates  are  removed  by  evaporation  and 
crystallization,  and  from  the  remaining  mother-liquor  iodine  is  ob- 
tained by  treating  the  liquor  with  manganese  dioxide  and  hydro- 
chloric (or  sulphuric)  acid : 

2KI  -f  MnO2  +  2H2SO4  =  K^SO^  +  MnSO4  +  2H2O  -f  21. 

The  liberated  iodine  distils,  and  is  collected  in  cooled  receivers. 
Sodium  nitrate  found  in  Chili  contains  a  small  quantity  of  sodium 
iodate,  and  the  mother-liquors,  from  which  the  nitrate  has  been  crystal- 
lized, contain  enough  iodate  to  be  employed  for  the  preparation  of  iodine. 

lodins  is  a  bluish-black,  crystalline  substance  of  a  somewhat 
metallic  lustre,  a  distinctive  odor,  a  sharp  and  acrid  taste,  and  a  neu- 
tral reaction.  Specific  gravity  4.948  at  17°  C.  (62.6°  F.).  It  fuses 
at  114°  C.  (237°  F.),  and  boils  at  180°  C.(356°  F.),  being  converted 
into  beautiful  purple-violet  vapors ;  also,  it  volatilizes  in  small  quanti- 
ties at  ordinary  temperature.  It  is  soluble  in  about  5000  parts  of 
water,  more  soluble  in  water  containing  salts,  for  instance,  potassium 
iodide ;  the  official  Liquor  iodi  compositus  (LugoPs  solution)  is  a 
preparation  based  on  this  property.  It  contains  5  parts  of  iodine  and 
10  parts  of  potassium  iodide  in  100  parts  of  aqueous  solution.  Iodine 
is  soluble  in  10  parts  of  alcohol,  very  soluble  in  ether,  disulphide  of 
carbon,  and  chloroform.  The  solution  of  iodine  in  alcohol  or  ether 
has  a  brown,  the  solution  in  disulphide  of  carbon  or  in  chloroform  a 
violet,  color.  Iodine  stains  the  skin  brown,  and  when  taken  inter- 
nally acts  as  an  irritant  poison. 

Tincture  of  iodine,  Tinctura  iodi,  is  a  dark  reddish-brown  solution 
of  70  grammes  of  iodine  and  50  grammes  of  potassium  iodide  in 
enough  alcohol  to  make  1000  c.c.  of  solution. 

The  increased  solubility  of  iodine  in  solutions  of  iodides,  or  of 
hydriodic  acid,  is  due  to  the  formation  of  definite  compounds  by  a  re- 
versible action,  thus, 

KI  +  21  ^±  KI3. 

The  brown  color  of  solutions  of  iodine  in  certain  solvents,  as  alcohol, 
ether,  etc.,  has  been  shown  to  be  due  to  a  feeble  combination  between 
one  molecule  of  iodine  and  one  molecule  of  the  solvent.  In  violet- 
colored  solutions  there  is  no  combination. 

Iodine  in  very  small  quantity  is  a  constituent  of  the  human  body  and  that 
of  animals.     The  greatest  portion  is  found  in  the  thyroid  gland,  as  a  complex 
16 


242  NON-METALS  AND   THEIR  COMBINATIONS. 

substance  known  as  tbyro-iodine,  which  is  of  great  value  in  certain  diseases, 
especially  cretinism,  resulting  from  deficient  development  of  the  thyroid  gland. 
Bauman  discovered  (1895)  iodine  in  this  gland.  The  thyroid  of  sheep,  which 
in  the  dried  form  is  official,  contains  0.17  per  cent,  of  iodine. 

Hydriodic  acid,  Acidum  hydriodicum,  HI  =  126.9.  This  is  a 
colorless  gas  readily  soluble  in  water ;  the  solution  is  unstable,  being 
easily  decomposed  with  liberation  of  iodine.  It  may  be  obtained  by 
processes  analogous  to  those  mentioned  for  the  preparation  of  hydro- 
bromic  acid.  The  action  of  hydrogen  sulphide  upon  iodine  in  the 
presence  of  water  is  as  follows  : 

H2S    +    21  2HI    +    S. 

The  official  method  for  making  diluted  hydriodic  acid  depends  on  the  decom- 
position of  an  aqueous  solution  of  potassium  iodide  by  an  alcoholic  solution  of 
tartaric  acid  in  the  presence  of  a  small  quantity  of  potassium  hypophosphite, 
which  acts  as  a  preservative.  Upon  cooling  the  mixture  to  the  freezing-point, 
acid  potassium  tartrate  separates,  while  hydriodic  acid  remains  in  solution, 
which  is  further  diluted  until  a  10  per  cent,  acid  is  obtained.  The  decomposi- 
tion taking  place  is  this : 

KI    +    H2C4H4O6    :       KHC4II4O6    -j-     HI. 

While  hydriodic  acid  itself  is  not  of  much  importance,  many  of 
its  salts,  the  iodides,  are  of  great  interest. 

At  0°  C.  an  aqueous  solution  can  be  obtained  containing  as  much  as  90  per 
cent.  HI.  Nearly  all  iodides  are  soluble  in  water.  The  insoluble  ones  are  of 
silver,  mercury,  copper  (ous).  Lead  iodide  is  sparingly  soluble. 

The  ionic  reactions  for  iodine  compounds  are  analogous  to  those  for  chlorine 
compounds. 

Tests  for  iodine  and  iodides. 

(Any  soluble  iodide  may  be  used.) 

1.  Add  to  solution  of  an  iodide,  solution  of  silver  nitrate:  a  pale- 
yellow  precipitate  of  silver  iodide,  Agl,  falls,  which  is  insoluble  in 
nitric  acid,  very  sparingly  soluble  in  ammonia  water,  but  soluble  in 
solution  of  sodium  thiosulphate  or  potassium  cyanide.     (See  Photog- 
raphy in  Chapter  31,  under  Silver.) 

2.  Add  lead  acetate  to  a  solution  of  an  iodide :  a  yellow  precipi- 
tate of  lead  iodide,  PbI2,  is  produced.     When  the  precipitate  is  dis- 
solved in  a  large  volume  (200  c.c.)  of  boiling  water,  and  the  solution 
is  cooled  slowly,  beautiful  golden  spangles  are  formed. 

3.  Add  mercuric  chloride  solution  to  a  solution  of  an  iodide  :  a  red 
precipitate  of  mercuric  iodide,  HgI2,  is  produced,  which  is  soluble  in 
solutions  of  mercuric  chloride  and  potassium  iodide.     Note  that  the 
corresponding  chloride  and  bromide  of  mercury  are  soluble  and  white. 


BR  OM1NE—  IODINE— FL  UORINE.  243 

Also  make  the  test  with  solution  of  mercurous  nitrate.  A  green- 
ish-yellow precipitate  of  mercurous  iodide,  Hgl,  is  obtained.  The 
corresponding  chloride  and  bromide  are  white  and  also  insoluble. 

4.  To  the  solution  of  an  iodide  add  some  chlorine  water,  or  a  few 
drops  of  concentrated  nitric  acid ;   iodine  is  liberated,  which,  with 
strongly  diluted  starch  solution,  gives  a  blue  color.     Iodine  in  com- 
bination has  no  action  on  starch.     Excess  of  chlorine  oxidizes  iodine 
to  colorless  iodic  acid ;  hen.ce,  the  same  precaution  must  be  used  as 
given  in  test  2  for  bromides. 

Traces  of  iodine  may  be  detected  readily  by  the  fine  violet  color 
given  to  chloroform  or  carbon  disulphide  when  the  liquid  is  shaken 
with  them. 

5.  Add  a  little  concentrated  sulphuric  acid  to  a  few  granules  of  an 
iodide  and  warm  gently.     Colorless  hydriodic  acid  gas  is  liberated, 
which   causes  white  fumes  with  the  moisture  of  the  air;  also  free 
iodine,  which  may  be  recognized  by  its  violet  vapor. 

Tests  3  and  4  are  usually  sufficient  to  identify  iodides  or  hydriodic 
acid. 

Iodic  acid,  HI03.  When  iodine  is  dissolved  in  strong  nitric  acid,  this  solu- 
tion being  then  evaporated  to  dryness  and  heated  to  about  200°  C.  (392°  F.) 
a  white  residue  remains,  which  is  iodine  pentoxide : 

61  -f  10HNO3  ==  5N2O2  +  5H2O  +  3I2O6. 
By  dissolving  this  oxide  in  water,  iodic  acid  is  obtained : 
IA  +  H20  =  2HI03. 

Iodic  acid  is  a  white  crystalline  substance,  very  soluble  in  water.  From 
iodic  acid  or  from  iodates,  sulphurous  acid  and  many  other  reducing  agents 
liberate  iodine. 

Hypoiodous  acid  and  its  salts  are  not  known.  Periodic  acid  and  its  salts 
can  be  obtained.  These  oxygen  compounds,  in  marked  contrast  to  those  of 
chlorine,  are  stable.  Iodine  pentoxide  is  the  only  oxide  of  the  element 
known. 

Sulphur  iodide,  Sulphuris  iodidum,  S2I2.  When  the  two  elements, 
sulphur  and  iodine,  are  mixed  together  in  the  proportion  of  their  atomic 
weights,  and  this  mixture  is  heated,  direct  combination  takes  place.  The 
fused  mass  is  grayish-black,  brittle,  has  a  'crystalline  fracture  and  a  metallic 
lustre.  It  is  almost  insoluble  in  water,  but  soluble  in  glycerin  and  in  carbon 
disulphide. 

Compounds  of  iodine  with  bromine  and  chlorine.  While  the  affinity 
between  the  halogens  is  feeble,  yet  a  few  compounds  formed  by  their  union  are 
known  ;  all  of  them  are  unstable,  decomposing  readily  on  heating  and  some 
also  in  contact  with  water.  Of  some  interest  is  iodine  trichloride,  IC13,  obtain- 
able as  an  orange,  crystalline  substance  by  passing  dry  chlorine  gas  over  iodine, 


244  NON-METALS  AND   THEIR  COMBINATIONS. 

when  at  first  iodine  monochloride,  IC1,  and  then  the  trichloride  is  formed.    The 
latter  has  been  used  as  a  disinfectant. 

Compounds  of  nitrogen  with  the  halogens.  When  chlorine  or  iodine 
acts  on  ammonia  the  hydrogen  of  the  latter  combines  with  the  halogens,  while 
nitrogen  is  either  set  free  or  also  enters  into  combination  with  the  halogens, 
thus: 

NH3  +  3C1  =  3HC1  +  N, 

NH3  +  6C1  ==  3HC1  -f  NC13. 

The  compounds  NH2C1  and  NHC12,  as  also  the  corresponding  iodine  com- 
pounds, are  known.  All  these  bodies  are  very  unstable ;  nitrogen  trichloride, 
an  oily  liquid,  is  one  of  the  most  explosive  substances  known  ;  nitrogen  iodide, 
a  black  powder,  also  explodes  readily. 

Fluorine,  F  =  18.9.  This  element  is  found  in  nature,  chiefly  as 
fluorspar,  calcium  fluoride,  CaF2 ;  traces  of  fluorine  occur  in  many 
minerals,  in  some  waters,  and  also  in  the  enamel  of  teeth,  and  in  the 
bones  of  mammals.  Fluorine  was,  until  1887,  scarcely  known  in  the 
elementary  state,  because  all  attempts  to  isolate  it  were  frustrated  by 
the  powerful  affinities  which  this  element  possesses,  and  which  render 
it  difficult  to  obtain  any  material  (from  which  a  vessel  may  be  made) 
which  is  not  chemically  acted  upon,  and,  therefore,  destroyed,  by 
fluorine.  'The  method  used  now  for  liberating  fluorine  depends  upon 
the  decomposition  of  hydrofluoric  acid  by  a  strong  current  of  electricity 
in  an  apparatus  constructed  of  platinum  with  stoppers  of  fluorspar. 
To  prevent  too  rapid  corrosion  of  the  platinum  vessels,  the  decom- 
position is  accomplished  at  a  temperature  below  the  freezing-point. 
Fluorine  is  a  gas  of  yellowish  color,  having  a  highly  irritating  and 
suffocating  odor,  and  possessing  affinities  stronger  than  those  of  any 
other  element.  As  a  supporter  of  combustion,  fluorine  leaves  oxygen 
far  behind ;  it  combines  spontaneously  even  in  the  dark  and  at  low 
temperature  with  hydrogen;  sulphur,  phosphorus,  lampblack,  and 
also  many  metals  ignite  readily  in  fluorine ;  even  the  noble  metals, 
gold,  platinum,  and  mercury,  are  converted  into  fluorides;  from 
sodium  chloride  the  chlorine  is  liberated  with  the  formation  of 
sodium  fluoride ;  organic  substances,  such  as  oil  of  turpentine,  alco- 
hol, ether,  and  even  cork  ignite  spontaneously  when  brought  in 
contact  with  this  remarkable  element. 

Hydrofluoric  acid,  HF.  A  colorless  gas,  very  irritating,  soluble 
in  water.  It  is  obtained  by  the  action  of  sulphuric  acid  on  fluorspar  : 

CaF2    +    H2SO<    =    2HF    +     CaSO4. 

Hydrofluoric  acid,  either  in  the  gaseous  state  or  its,  solution  in 


BROMINE-IODINE-FL  UOttINK  245 

water,  is  used  for  etching  on  glass.  This  effect  is  due  to  the  action  of 
the  acid  upon  the  silica  of  the  glass,  which  is  converted  into  either 
silicon  fluoride,  SiF4 ;  or  into  hydrofl uosilicic  acid,  H2SiF6. 

Hydrofluoric  acid,  or  strong  solutions  of  it,  are  powerful  antiseptics.  In 
small  quantities  the  acid  is  used  as  an  admixture  to  fermenting  liquids,  as  it 
has  been  found  that  it  does  not  act  upon  the  principal  ferment  of  yeast,  which 
causes  the  decomposition  of  sugar  into  alcohol  and  carbon  dioxide,  while  it 
readily  destroys  a  number  of  objectionable  ferments.  The  yield  of  alcohol  is 
thus  considerably  increased. 

Experiment  19,  Prepare  a  glass  plate  by  heating  it  slightly  and  covering  its 
surface  with  a  thin  layer  of  wax  or  paraffin ;  after  cooling,  scratch  some  letters 
or  figures  through  the  wax,  thus  exposing  the  glass.  Set  the  plate  over  a  dish 
(one  made  of  lead  or  platinum  answers  best),  in  which  a  few  grammes  of  pow- 
dered fluorspar  have  been  mixed  with  about  an  equal  weight  of  sulphuric  acid, 
and  set  in  the  open  air  for  a  few  hours  (heating  slightly  facilitates  the  action); 
upon  removing  the  wax  or  paraffin,  the  glass  will  be  found  to  be  etched  where 
its  surface  was  exposed  to  the  vapors  of  the  acid.  This  experiment  serves  also 
as  the  best  test  for  fluorides.  (See  under  Silicon,  p.  186.) 

QUESTIONS. — How  is  bromine  found  in  nature?  State  the  physical  and 
chemical  properties  of  bromine.  What  is  hydrobromic  acid,  and  how  can  it  be 
made  ?  By  what  tests  may  bromine  and  bromides  be  recognized  ?  What  is  the 
chief  source  of  iodine?  What  are  the  chemical  and  physical  properties  of 
iodine?  What  is  tincture  of  iodine,  what  is  its  color,  and  how  does  it  stain 
the  skin  ?  Mention  reactions  by  which  iodine  and  iodides  may  be  recognized. 
By  what  element  may  bromine  and  iodine  be  liberated  from  their  compounds? 
How  is  hydrofluoric  acid  made,  and  what  is  it  used  for? 


IV. 
METALS  AND  THEIR  COMBINATIONS. 


Cobalt, 
Copper, 


20.  GENERAL  REMARKS  REGARDING  METALS. 

OF  the  total  number  of  sixty  metallic  elements  only  about  one-half 
are  of  sufficient  general  interest  and  importance  to  deserve  considera- 
tion in  this  book. 

Derivation  of  names,  symbols,  and  atomic  weights. 

Aluminum,        Al   =     26.9.      From  alum,  a  salt  containing  it. 
Antimony,          Sb    =  119.3.      From  the  Greek  avrl  (anti),  against,  and  raotne,  a 
(Stibium.)  French  word  for  monk,  from  the  fact  that  some 

monks  were  poisoned  by  compounds  of  antimony. 
Stibium,  from  the  Greek,  orijSi  (stibi),  the  name 
for  the  native  sulphide  of  antimony. 
Arsenic,  As   =     74.4.      From  the  Greek  aposvucbv  (arsenicon),  the  name  for 

the  native  sulphide  of  arsenic. 

Barium,  Ba   =  136.4       From  the  Greek  fiapvs  (barys),  heavy,  in  allusion  to 

the  high  specific  gravity  of  barium  sulphate,  or 
heavy-spar. 

From  the  German  wixmuth,  an  expression  used  long 
ago  by  the  miners  in  allusion  to  the  variegated 
tints  of  the  metal  when  freshly  broken. 
From  the  Greek  nadfida  (kadmeia)  the  old  name  for 
calamine  (zinc  carbonate),  with  which  cadmium 
is  frequently  associated. 

Calcium,  Ca    =     39.8.      From  the  Latin  calx,  lime,  the  oxide  of  calcium. 

Chromium,         Cr    =    51.7.       From  the  Greek  XP"/^a  (chroma),  color,  in  allusion 

to  the  beautiful  colors  of  all  its  compounds. 
Co    =    58.56,     From  the  German  Kobold,  which  means  a  demon 

.  inhabiting  the  mines. 

Cu  =    63.1.  '    From  the  Latin  cuprum,  copper,  and  this  from  the 
Island  of  Cyprus,  where  copper  was  first  obtained 
by  the  ancients. 
Gold,  Au  =  195.7.      Gold  means  bright  yellow  in  several  old  languages. 

(Aurum.)  The  Latin  aurum  signifies  the  color  of  fire. 

Iridium,  Ir     =  191.5.       From  iris,  rainbow,  in  allusion  to  the  varying  tints 

of  its  salt  solutions. 

Fe    =     55.5.       Iron  probably  means  metal;   the  derivation  of  the 
Latin  ferrum  is  not  definitely  known. 

247 


Bismuth,  Bi    =  206.9. 


Cadmium,          Cd    =111.6. 


Iron, 


248 


METALS  AND   THEIR   COMBINATIONS. 


Lead,  Pb 

(Plumbum.) 

Lithium,  Li 

Magnesium,  Mg 


=  205.35.    Both  words  signify  something  heavy. 


6.98. 
24.18. 


Manganese,        Mn  =     54.6. 

198.5. 


Mercury,  Hg 

(Hydrargyrum  ) 

Molybdenum,    Mo 

Nickel,  Ni 


95.3. 

58.3. 


Platinum,  Pt    =  193.3. 

Potassium,         K     —    38.86. 
(Kalium.) 


Silver,  Ag 

(Argentum.) 

Sodium,  Na 

(Natrium.) 


107.12. 

22.88. 


Strontium,         Sr    =     86.94. 
118.1. 
64.9. 


Tin,  Sn 

(Stannum.) 
Zinc,  Zn 


From  the  Greek  Weiog  (litheios),  stony. 
From  Magnesia,  a  town  in  Asia  Minor,  where  mag- 
nesium carbonate  was  found  as  a  mineral. 
Probably  from  magnesium,  with  the  compounds  of 

which  it  was  long  confounded. 
From  Mercury,  the  messenger  of  the  Greek  gods. 

Hydrargyrum  means  liquid  silver. 
From  the  Greek  n6"kvfi6og  (molybdos),  lead. 
From  the  old   German   word  nickel,  which  means 

worthless. 
Platina  is  the  diminutive  of  the  Spanish  word  plata, 

silver. 
From  pot-ash  ;  potassium  carbonate  being  the  chief 

constituent  of  the  lye  of  wood-ashes.     Kali  is  the 

Arabic  word  for  ashes. 
Both  words  signify  white. 

From  soda-ash,  or  sod-ash,  the  ashes  of  marine  plants 
which  are  rich  in  sodium  carbonate  Natron  is  an 
old  name  for  natural  deposits  of  sodium  carbonate. 

From  Strontian,  a  village  in  Scotland,  where  stron- 
tium carbonate  is  found. 

Both  words  most  likely  signify  stone. 

Most  likely  from  the  German  zinn  or  tin,  the  metals 
having  been  confounded  with  each  other. 


Melting-points  of  metals. 

c.  F. 

Fusible  below  the  f  Mercury 40°          40° 

boiling-point  of  -[  Potassium          .         .         .            -f  62  -f-144 

water,                  ^  Sodium 97  207 

f  Lithium    .....     180  356 

I  Tin 228  443 

Cadmium  ......    310  590 

Bismuth 260  500 

Lead 325  617 

Zinc 412  773 

Magnesium        .         .        .         .700  1292 

Antimony          ....    425  797 

Aluminum         .                               700  1292 

Barium. 

Calcium. 

Strontium. 


Fusible  below  red 
heat, 


Fusible 
heat, 


at     red 


TIME  OF  DISCOVERY  OF  THE  METALS. 


249 


r  Silver 

Copper 

Gold 

Cast-  iron  . 

Pure  iron, 

Infusible  below  a 

Nickel, 

red  heat. 

Cobalt, 

Manganese, 

Molybdenum,     ^ 

Chromium,         J 

Platinum,             1 

Iridi.um,               •» 

1020 
1100 
1200 
1150 


1868 
2012 
2192 
2102 


Highest  heat  of  forge. 

|  Agglomerate,  but  do  not  melt  in  forge. 
Fusible  in  the  oxyhydrogen  blowpipe 


flame. 


Arsenic  does  not  fuse,  but  volatilizes  at  a  low  red  heat. 


Specific  gravities  of  metals  at  15.5°  C, 


^lithium 

Potassium 

Sodium 

Calcium 

Magnesium  . 

Strontium 

Aluminum     . 

Barium 

Arsenic 

Antimony 

Zinc 

Tin 

Iron 


0.593 

0.865 

0.972 

1.57 

1.75 

2.54 

2.67 

4.00 

5.88 

6.72 

6.90 

7.29 

7.79 


Manganese 
Molybdenum 
Cadmium 
Nickel      . 
Cobalt      . 
Copper     . 
Bismuth    . 
Silver 
Lead 

Mercury  . 
Gold 

Platinum  . 
Iridium 


800 

863 

870 

870 

8.95 

896 

990 

10.50 

11.36 

1359 

19.36 

21.50 

22.42 


Time  of  discovery  of  the  metals. 


Gold, 

Silver, 

Mercury, 

Copper, 

Zinc, 

Tin, 

Iron, 

Lead, 

Antimony, 

Bismuth, 

Arsenic, 

Cobalt, 

Platinum, 

Nickel, 

Manganese, 

Molybdenum, 

Chromium, 

Iridium, 


These  metals  were  known  to  the  ancients,  because 
either  they  are  found  in  a  metallic  state,  or  can  be 
obtained  by  comparatively  simple  processes  from 
the  oxides. 


J 

|  Latter  part  of  the  fifteenth  century. 

1694,  by  Schroder. 

1733,  by  Brandt. 

1741,  by  Wood. 

1751,  by  Cronstedt. 

1774,  by  Galm. 

1782,  by  Hjelm. 

1797,  by  Vauquelin. 

1804,  by  Smithson  Tennant. 


250 


METALS  AND   THEIR   COMBINATIONS. 


Potassium, 

Sodium, 

(  H 

Barium, 

.      1807-1808     •] 

Calcium, 

I 

Strontium, 

Magnesium,     J 

Cadmium,            1817,  by  Stromeyer. 

Lithium,              1817,  by  Arfvedson. 

Aluminum,          1828,  by  Wohler. 

Davy  discovered  methods  for  the 
separation  of  these  metals  from 
their  oxides. 


Valence  of  metals.1 


Univalent. 

Lithium, 

Potassium, 

Sodium, 

Silver. 


Bivalent. 

Barium, 

Calcium, 

Strontium, 

Magnesium, 

Cadmium, 

Zinc, 

Copper, 

Mercury. 

Trivalent. 
Aluminum, 


Bi,  tri,  or  sexivalent. 
Chromium, 
Cobalt, 
Iron, 

Manganese, 
Nickel, 
Molybdenum. 

Bi-  and  quadrivalent. 
Iridium, 
Platinum, 
Tin. 


Tri-  and  quinquivalent. 

Antimony, 

Arsenic, 
,        Bismuth. 

Uni-  or  trivalent. 
Gold. 


Occurrence  in  nature. 

a.  In  a  free  or  combined  state. 

Almost  exclusively  in  the  metallic  state. 


Gold, 

Iridium, 

Platinum, 

Silver, 

Mercury, 

Bismuth,  generally  metallic,  also  as  oxide  and  sulphide. 

Copper,  rarely  metallic ;  chiefly  as  sulphide,  oxide,  and  carbonate 


I  As  metals  or  sulphides. 


Potassium, 

Sodium, 

Lithium, 


6.  In  combination  only. 
Chiefly  as  chlorides  or  silicates. 


1  The  valence  here  given  is  the  one  chiefly  exerted  by  the  elements,  but  several  compounds 
are  known  in  which  some  of  the  metals  exhibit  a  yet  different  valence ;  thus  copper  and  mer- 
cury seem  to  be  univalent  in  certain  compounds,  while  some  metals  exhibiting  a  valence  of 
six  (iron,  chromium,  etc.)  are  also  bi-  and  trivalent. 


CLASSIFICATION   OF  METALS.  251 

Barium,  as  sulphate. 

Calcium,  \ 

Strontium,         >•  As  carbonates,  sulphates,  silicates. 

Magnesium,     J 

Aluminum,  in  silicates. 

Iron,  ^ 

Zinc,  [•  As  oxides,  carbonates,  sulphide. 

Cadmium,         J 

Arsenic, 

Antimony, 

Cotit,  Chiefly  as  sulphides. 

Nickel, 

Molybdenum,  J 

Chromium,       ^ 

Manganese,       >•  Chiefly  as  oxides. 

Tin, 

Classification  of  metals. 

For  the  purpose  of  study,  metals  may  be  differently  arranged  into 
groups  according  to  the  selection  of  those  properties  which  are  made 
the  basis  for  comparison.  Thus,  the  valence  alone  may  serve  for 
classification,  and  in  that  case  the  arrangement  will  also  largely  cor- 
respond to  the  periodic  system.  The  scheme  adopted  below  is  based 
more  especially  on  the  analytical  behavior  of  the  metals.  While 
this  classification  brings  together  in  many  cases  those  metals  belong- 
ing to  one  group  of  the  periodic  system,  in  a  few  cases  the  elements 
of  one  periodic  group  are  separated,  as  for  instance  in  the  case  of 
magnesium,  zinc,  and  cadmium.  These  elements  resemble  one 
another  closely  in  many  respects,  and  are  found  together  in  group 
II.  of  the  periodic  system,  while  in  a  classification  based  chiefly  on 
analytical  properties  these  metals  are  found  in  different  groups. 

Light  metals.  Heavy  metals. 

Sp.  gr.  from  0  6  to  4.  Sp  gr.  from  6  to  22.4. 

Sulphides  soluble  in  water.  Sulphides  insoluble  in  water. 

Light  metals. 

Earth  metals.  Alkaline  earth  metals.  Alkali-metal. 

Al,  and  many  rare  metals.  Ba,  Ca,  Sr,  (Mg).  K,  Na,  Li,  (NH4). 

Oxides  insoluble.  Oxides  soluble ;  Oxides,  carbonates,  and 

Carbonates  insoluble.  most  salts  soluble. 

Heavy  metals. 

Arsenic  group.  Lead  group.  Iron  group. 

As,  Sb,  Sn,  Au,  Pt,  Mo.        Pb,  Cu,  Bi,  Ag,  Hg,  Cd.  Fe,  Co,  Ni,  Mn,  Zn,  Cr. 

— -v —  Sulphides  soluble  in 

Sulphides  insoluble  in  dilute  acids.  dilute  acids. 


Sulphides  soluble  in  am-       Sulphides  insoluble  in 
monium  sulphide.  ammonium  sulphide. 


252  METALS  AND  THEIR  COMBINATIONS. 

Properties  of  metals.  All  metals  have  a  peculiar  lustre  krrown 
as  metallic  lustre,  and  all  are  more  or  less  good  conductors  of  heat 
and  electricity.  The  color  of  most  metals  is  white,  grayish,  or 
bluish-white,  or  dark  gray ;  a  few  metals  show  a  distinct  color,  as, 
for  instance,  gold  (yellow)  and  copper  (red). 

At  ordinary  temperatures  metals  are  solids  with  the  exception  of 
mercury,  all  are  fusible,  and  some  are  so  volatile  that  they  may  be 
distilled.  Most,  probably  all,  metals  may  be  obtained  in  a  crystal- 
lized condition. 

Metals  show  a  wide  difference  in  the  properties  of  malleability,  ductility,  and 
tenacity.  Gold  is  both  the  most  malleable  and  most  ductile  metal,  while  lead 
possesses  comparatively  little  of  these  qualities.  In  many  cases  heat  increases 
or  develops  malleability  and  ductility,  but  diminishes  tenacity ;  however,  the 
tenacity  of  iron,  which  surpasses  that  of  any  other  metal,  is  not  lessened  by 
heating. 

The  term  annealing  denotes  the  process  of  restoring  the  malleability  and 
ductility  of  some  metals  after  these  properties  have  been  diminished,  by  caus- 
ing a  change  in  the  molecular  structure  of  the  metals  through  hammering, 
rolling,  or  sudden  cooling.  Annealing  consists  in  heating  the  metal  and  per- 
mitting it  to  cool  slowly  (in  a  few  cases  quickly)  in  order  to  allow  the  cohesive 
force  to  produce  the  most  stable  arrangement  of  the  molecules. 

Tempering,  which  term  at  times  is  used  analogously  with  annealing,  consists 
in  heating  the  metal  and  chilling  it  suddenly.  The  result  of  annealing  is  the 
highest  development  of  softness  and  in  case  of  some  metals  the  restoration  of 
cohesiveness ;  the  object  of  tempering  is  the  attainment  of  a  certain  degree  of 
hardness  and  elasticity. 

Elasticity,  i.  e.,  the  power  of  recovering  original  form  when  twisted  or  bent, 
and  sonorousness,  i.  e.,  the  property  of  yielding  a  musical  sound  when  struck, 
are  possessed  only  by  the  harder  metals,  and  to  a  high  degree  by  certain 
mixtures  of  metals. 

All  metals  expand  when  heated,  but  the  rate,  of  expansion  of  the  different 
metals  differs.  Within  certain  limits  of  temperature  the  expansion  of  a  metal 
occurs  uniformly  in  direct  ratio  to  the  increase  in  temperature.  The  great 
expansibility  of  zinc  is  an  important  property  of  the  metal  when  used  as  a  die 
in  dental  prosthesis. 

Metals  do  not  combine  chemically  with  one  another.  Their  mix- 
tures (alloys)  still  exhibit  the* metallic  nature  in  their  general  physical 
characters.  It  is  different,  however,  when  metals  combine  with  non- 
metals  ;  in  this  case  the  metallic  characters  are  lost  almost  invariably. 
All  metals  combine  with  chlorine,  fluorine,  and  oxygen ;  most  metals 
also  with  sulphur,  bromine,  and  iodine ;  many  also  with  carbon  and 
phosphorus,  forming  the  respective  chlorides,  fluorides,  oxides,  sul- 
phides, bromides,  iodides,  carbides,  and  phosphides.  Metals  replace 
hydrogen  in  acids,  forming  salts. 


PROPERTIES  OF  METALS.  253 

The  intensity  with  which  metals  combine  with  non-metals  or  with  acids 
differs  widely.  Selecting  the  combinations  with  oxygen  as  a  typical  instance 
we  find  that  the  affinity  between  the  alkali  metals  and  the  alkaline  earth 
metals  is  so  intense  that  these  metals  cannot  be  exposed  to  the  atmosphere  for 
even  a  few  hours  without  undergoing  complete  oxidation.  It  is  for  this  reason 
that  these  metals  cannot  be  used  in  the  metallic  state  for  purposes  requiring 
constant  exposure  to  air.  Other  metals,  such  as  iron,  will  oxidize  (rust)  slowly 
at  ordinary  temperature  or  will  burn  when  heated  sufficiently  high.  Yet  other 
metals  retain  their  metallic  lustre  in  dry  or  moist  air  at  low  or  high  tempera- 
ture. Indeed,  the  oxides  of  these  metals  are  decomposed  into  oxygen  and  the 
respective  metal  by  the  mere  application  of  heat.  The  metals  showing  this 
behavior  are  often  called  noble  mefals,  while  all  others  are  designated  as  base 
metals.  The  noble  metals  are  gold,  silver,  mercury,  platinum,  iridium,  and  a 
few  other  metals  related  to  platinum.  (See  also  page  198.) 

Manufacture  of  metals.  Most  metals  may  be  obtained  from  their 
oxides  by  heating  the  latter  with  charcoal,  the  carbon  combining  with 
the  oxygen  of  the  oxide,  while  the  metal  is  liberated  : 

MO  +  C  =  CO    +    M; 
or 

2MO  +  C  =  CO2  +  2M. 

Also  hydrogen  may  be  used  in  some  cases  as  the  deoxidizing  agent : 

MO  +  2H  =  H20  -f  M. 

Some  metals  are  found  in  nature  chiefly  as  sulphides,  which  usually 
are  converted  into  oxides  (before  the  metal  can  be  obtained)  by  roast- 
ing. The  term  roasting,  when  used  in  metallurgy,  means  heating 
strongly  in  an  oxidizing  atmosphere,  when  the  sulphides  are  con- 
verted into  sulphates  or  oxides,  thus : 

MS   +   4O   =   MS04;  or  MS   +   3O  =  MO   +   SO2. 

A  few  metals  are  obtained  by  heating  the  chloride  with  metallic 
sodium,  when  sodium  chloride  is  formed,  while  the  other  metal  is 
set  free.  Electrolysis  is  also  one  of  the  means  for  obtaining  metals 
from  their  compounds. 

Recently  a  generally  applicable  method  of  obtaining  metals  has  been  devised, 
which  consists  in  the  action  of  aluminum  powder  on  the  oxides  of  the  metals, 
especially  of  those  that  have  a  high  fusing-point  and  form  difficultly  reducible 
oxides.  So  much  heat  is  developed  in  these  reductions  that  the  method  may  be 
used  for  welding,  for  example,  the  joints  between  rails. 

Alloys  are  combinations  or,  more  correctly  speaking,  mixtures  of 
two  or  more  metals.  Whenever  mercury  is  a  constituent  of  an  alloy 
it  is  called  amalgam.  All  alloys  exhibit  metallic  nature  in  their 
physical  properties— i.  e.,  they  have  metallic  lustre  and  are  more  or 
less  good  conductors  of  heat  and  electricity. 


254  METALS  AND   THEIR   COMBINATIONS. 

While  alloys  are  generally  looked  upon  as  molecular  mixtures,  and 
not  as  definite  chemical  compounds,  yet  there  are  many  alloys  the 
properties  of  which  are  not  intermediate  between  those  of  the  elements 
entering  into  these  alloys,  as  we  should  expect  if  they  were  mechanical 
mixtures.  For  this  reason  it  is  assumed  that,  in  at  least  some  cases, 
compounds  are  formed  which,  however,  are  generally  dissolved  in,  or 
mixed  with,  an  excess  of  one  of  the  constituent  metals. 

On  the  other  hand,  there  are  cases  where  there  is  an  utter  lack  of 
affinity  between  the  component  parts  of  an  alloy.  Thus,  alloys  of 
copper  and  lead,  usually  termed  pot-metal  alloys,  show  particles  of  the 
two  metals  side  by  side,  when  the  fractured  surface  is  examined  with 
the  microscope. 

Manufacture  of  alloys.  Alloys  are  generally  obtained  by  fusing  the 
metals  together ;  but  in  order  to  do  it  successfully  such  properties  of  the  com- 
ponents as  fusibility,  specific  gravity,  proneness  to  oxidize,  etc.,  should  be  con- 
sidered. As  a  general  rule  the  metal  having  the  highest  fusing-point  is  melted 
first,  and  to  it  are  added  the  other  metals  in  the  diminishing  order  of  their 
fusing- points.  Loss  or  deterioration  by  oxidation  should  be  guarded  against 
by  covering  the  surface  of  the  liquid  mass  with  charcoal  or  with  such  fluxes  as 
borax,  sodium  chloride,  or  ammonium  chloride.  The  heat  should  at  no  time 
be  higher  than  is  necessary  for  the  liquefaction. 

Properties  of  alloys.  Alloys  generally  are  harder  and  more  brittle,  but 
less  ductile  and  malleable  than  the  constituent  metals  possessing  these  qualities 
in  the  highest  degree.  The  union  even  of  two  ductile  metals  may  destroy  that 
property  more  or  less  completely,  as  is  shown  by  the  absence  of  ductility  in  an 
alloy  of  gold  and  a  small  portion  of  lead.  The  combination  of  a  brittle  and  a 
ductile  metal  always  yields  a  brittle  alloy. 

Tenacity  is  generally  increased.  Thus,  copper  alloyed  with  12  per  cent,  of 
tin  has  its  tenacity  trippled ;  gold,  when  alloyed  with  copper,  silver,  or  plat- 
inum, has  its  tensile  resistance  nearly  doubled ;  aluminum  bronze,  an  alloy  of 
copper  and  aluminum,  has  a  greater  tenacity  than  that  of  either  of  the  con- 
stituent metals. 

Certain  metals  impart  to  alloys  specific  properties.  Thus,  bismuth  and 
cadmium  increase  fusibility;  tin  and  lead,  both  of  which  are  soft  metals, 
impart  hardness  and  tenacity  ;  arsenic  and  antimony  produce  brittle  alloys. 

QUESTIONS. — How  many  metals  are  known,  and  about  how  many  are  of  gen- 
eral interest?  Mention  some  metals  having  very  low  and  some  having  very 
high  fusing-points.  What  range  of  specific  gravities  do  we  find  among  the 
metals  ?  Mention  some  univalent  and  some  bivalent  metals  ;  also  some  which 
show  a  different  valence  under  different  conditions.  Mention  some  metals  which 
are  found  in  nature  in  an  uncombined  state;  some  which  are  found  as  oxides, 
sulphides,  chlorides,  and  carbonates,  respectively.  Into  what  two  groups  are 
the  metals  divided?  State  the  three  groups  of  light  metals.  What  is  a  metal  ? 
What  is  an  alloy,  and  what  is  an  amalgam  ?  By  what  process  can  most  metals 
be  obtained  from  their  oxides? 


POTASSIUM.  255 

The  fusibility  of  an  alloy  is  invariably  greater  than  that  of  its  least  fusible 
constituent,  and  may  be  greater  than  that  of  its  most  fusible  constituent.  Thus 
an  alloy  of  2  parts  of  tin,  3  of  lead,  and  5  of  bismuth  fuses  at  91°  C.,  while 
tin  alone  melts  at  228°,  lead  at  325°,  and  bismuth  at  260°  C. 

The  conductivity  of  alloys  for  heat  and .  electricity  is  less  than  that  of  the 
pure  metals.  The  color  of  alloys  is  generally  a  modification  of  the  predom- 
inating ingredient,  but  instances  are  known  where  the  color  of  alloys  has  no 
relation  to  its  constituents.  For  instance,  German  silver  is  perfectly  white 
although  it  contains  a  considerable  portion  of  red  copper. 

21.    POTASSIUM  (KALIUM). 

K'  =  39  (38.86). 

General  remarks  regarding-  alkali-metals.  The  metals  potas- 
sium, sodium,  lithium  (rubidium  and  caesium)  form  the  group  of  the 
alkali-metals,  which,  in  many  respects,  show  a  great  resemblance  to 
each  other  in  chemical  and  physical  properties.  For  reasons  to  be 
explained  hereafter,  the  compound  radical  ammonium  is  usually 
classed  among  the  alkali-metals. 

The  alkali-metals  are  all  univalent;  they  decompose  water  at  the 
ordinary  temperature,  with  liberation  of  hydrogen;  they  combine 
spontaneously  with  oxygen  and  chlorine ;  their  hydroxides,  sulphates, 
nitrates,  phosphates,  carbonates,  sulphides,  chlorides,  iodides,  and 
nearly  all  other  of  their  salts  are  soluble  in  water ;  all  these  com- 
pounds are  white,  solid  substances,  most  of  which  are  fusible  at  a 
red  heat.  Of  all  metals,  those  of  the  alkalies  are  the  only  ones  form- 
ing hydroxides  and  carbonates  which  are  not  decomposed  by  heat. 

The  metals  themselves  are  of  a  silver-white  color,  and  extremely 
soft;  on  account  of  their  tendency  to  combine  with  oxygen  they 
must  be  kept  in  a  liquid,  such  as  coal-oil,  which  is  not  acted  on  by 
them,  or  in  an  atmosphere  of  hydrogen. 

The  metals  may  be  obtained  by  heating  their  carbonates  with 
carbon  in  iron  retorts,  the  escaping  vapors  being  passed  under  coal- 
oil  for  condensation  of  the  metal : 

K2C03   +   20  =  3CO   +   2K. 

At  present  most  of  the  alkali  metals  are  obtained  by  the  electrol- 
ysis of  the  fused  hydroxides,  the  metal  and  hydrogen  being  liberated 
at  the  negative,  oxygen  at  the  positive  pole  : 
KOH  ==  K  4-  H  +  O. 

Occurrence  in  nature.  Potassium  is  found  in  nature  chiefly  as  a 
double  silicate  of  potassium  and  aluminum  (granite  rocks,  feldspar, 
and  other  minerals),  or  as  chloride  and  nitrate.  By  the  gradual  dis- 
integration of  the  different  granite  rocks  containing  potassium  silicate, 


256  METALS  AND   THEIR   COMBINATIONS. 

this  has  entered  into  the  soil,  whence  it  is  taken  up  by  plants  as  one 
of  the  necessary  constituents  of  their  food. 

In  the  plant  potassium  enters  largely  into  the  combination  of 
organic  compounds,  and  when  the  plant  is  burned  ashes  are  left 
containing  the  potassium,  now  in  the  form  of  carbonate.  By  ex- 
tractincr  such  ashes  with  water,  the  potassium  carbonate,  along  with 
small  quantities  of  chlorides  and  sulphates  of  potassium  and  sodium, 
is  obtained  in  solution,  by  the  evaporation  of  which  to  dryness  an 
impure  article  is  obtained,  known  as  crude  potash.  Formerly  this 
was  the  chief  source  of  potassium  compounds,  but  about  the  year 
1850  the  inexhaustible  salt  mines  of  Stassfurt,  Germany,  were  discov- 
ered. The  salt  there  mined  contains,  besides  the  chlorides  and  sul- 
phates of  sodium,  magnesium,  calcium,  and  other  salts,  considerable 
quantities  of  potassium  chloride,  and  the  Stassfurt  mines  at  present 
are  practically  the  source  of  all  potassium  compounds. 

Potassium  hydroxide,  Potassii  hydroxidum,  KOH  ==  55.74 
(Caustic  potash),  may  be  obtained  by  the  action  of  the  metal  on  water  : 

K  -h  H,O  =  H  +  KOH 

The  usual  process  for  making  potassium  hydroxide  is  to  boil  together 
a  dilute  solution  of  potassium  carbonate  or  bicarbonate  and  calcium 

hydroxide : 

K2C03  +  Ca(OH)2  =  CaC03  +  2KOH. 

Large  quantities  of  high-grade  potassium  hydroxide  are  now 
manufactured  directly  from  the  chloride  by  electrolysis. 

Experiment  20.  Add  gradually  5  grammes  of  calcium  hydroxide  (slaked 
lime)  to  a  boiling  solution  of  about  5  grammes  of  potassium  carbonate  in  50 
c.c.  of  water,  and  continue  to  boil  until  the  conversion  of  potassium  carbonate 
into  hydroxide  is  complete.  This  can  be  shown  by  filtering  off  a  few  drops  of 
the  liquid,  and  supersaturating  with  dilute  hydrochloric  acid,  which  should  not 
cause  effervescence.  Set  aside  to  cool,  and  when  all  solids  have  subsided,  pour 
off  the  clear  solution  of  potassium  hydroxide,  which  may  be  used  for  Experi- 
ment 21 .  What  quantities  of  K2CO3  and  Ca(OH)2  are  required  to  make  one  liter 
of  a  5  per  cent,  solution  of  potassium  hydroxide  ? 

Potassium  hydroxide  is  a  white,  hard,  highly  deliquescent  sub- 
stance, soluble  in  0.5  part  of  water  and  2  parts  of  alcohol ;  it  fuses 
at  a  low  red  heat,  forming  an  oily  liquid,  which  may  be  poured  into 
suitable  moulds  to  form  pencils;  at  a  strong  red  heat  it  is  slowly 
volatilized  without  decomposition;  it  is  strongly  alkaline  and  a 
powerful  base,  readily  combining  with  all  acids ;  it  rapidly  destroys 
organic  tissues,  and  when  taken  internally  acts  as  a  powerful  corrosive, 
and  most  likely  otherwise  as  a  poison- 


POTASSIUM.  257 

Antidotes  :  dilute  acids,  vinegar,  to  form  salts ;  or  fat,  oil,  or  milk,  to  form  soap. 
Liquor  potassii  hydroxidi  is  a  5  per  cent,  solution  of  potassium  hydroxide  in 
water. 

Potassium  oxide,  K2O.  This  compound  can  be  obtained  either 
by  burning  potassium  in  air  and  subsequent  heating  of  the  product 
to  a  high  temperature,  or  by  fusing  together  potassium  hydroxide 
and  metallic  potassium  : 

2KOH  -f  2K  =  2K2O  +  2H. 

Besides  this  potassium  monoxide,  corresponding  to  water  in  its  composition, 
two  other  oxides  of  the  composition  K2O2  (corresponding  to  hydrogen  perox- 
ide, H2O2)  and  K2O4  are  known.  The  latter  oxide  is  obtained  by  the  com- 
bustion of  potassium  in  oxygen.  It  is  a  strong  oxidizing  agent,  and  at  a  high 
temperature  is  decomposed  into  oxide  and  oxygen. 

Potassium  carbonate,  Potassii  carbonas,  K2CO3  =  137.27,  is 
obtained  from  wood-ashes  in  an  impure  state  as  described  above,  or 
from  the  native  chloride  by  the  so-called  Leblanc  process,  which  will 
be  described  in  connection  with  sodium  carbonate.  It  is  also  made 
by  passing  carbon  dioxide  into  solution  of  potassium  hydroxide, 
obtained  by  the  electrolytic  process. 

Pure  potassium  carbonate  is  obtained  by  heating  the  bicarbonate, 
which  is  decomposed  as  follows  : 

2KHCO3  =  K2CO3  +  H2O  +  CO2. 

Potassium  carbonate  is  deliquescent,  is  soluble  in  about  an  equal 
weight  of  water,  insoluble  in  alcohol,  and  has  strong  basic  and  alka- 
line properties. 

The  strong  alkaline  reaction  of  potassium  and  sodium  carbonate  in  solution 
is  due  to  hydrolysis  of  the  salts  into  bicarbonate,  which  is  neutral  to  litmus  and 
free  alkali.  (See  pages  122  and  201.) 

K2C03  +  H20  =  KHCO3  +  KOH. 

Potassium  bicarbonate,  Potassii  bicarbonas,  KHCO3  =  99.41. 
Obtained  by  passing  carbon  dioxide  through  a  strong  solution  of 
potassium  carbonate,  when  the  less  soluble  bicarbonate  forms  and 
separates  into  crystals  : 

K2CO3    +    H2O    +    CO2  2KHC03. 

Potassium  percarbonate,  K2C2O6,  also  exists  as  a  bluish-white  powder, 
which  liberates  oxygen  when  heated,  and  in  dilute  acid  solution  gives  off  hydro- 
gen dioxide.     It  is  obtained  by  electrolysis  of  a  concentrated  solution  of  potas- 
sium carbonate  at  about  —10°  C.  (14°  F.).     It  is  a  good  oxidizer. 
17 


258  METALS  AND  THEIR   COMBINATIONS. 

Potassium  nitrate,  Potassii  nitras,  KNO3  =  100.43  (Niter,  Salt- 
peter). Potassium  and  sodium  nitrate  are  found  as  an  incrustation  upon 
and  throughout  the  soil  of  certain  localities  in  dry  and  hot  countries, 
as,  for  instance,  in  Peru,  Chile,  and  India.  The  formation  of  these 
nitrates  is  to  be  explained  by  the  absorption  of  ammonia  by  the  soil, 
where  it  gradually  is  oxidized  and  converted  into  nitric  acid.  This 
nitrification,  i.4.9  the  conversion  of  ammonia  into  nitric  acid,  seems  to 
be  due  largely  to  the  action  of  micro-organisms,  termed  the  nitrifying 
ferment.  The  acid  after  being  formed  combines  with  the  strongest 
base  present  in  the  soil.  If  this  base  be  potash,  potassium  nitrate 
will  be  formed  ;  if  soda,  sodium  nitrate ;  if  lime,  calcium  nitrate. 

Upon  the  same  principle  is  based  the  manufacture  of  niter  on  a  large  scale, 
which  is  accomplished  by  mixing  animal  refuse  matter  with  earth  and  lime, 
and  placing  the  mixture  in  heaps  under  a  roof  to  prevent  lixiviation  by  rain. 
By  decomposition  (putrefaction)  of  the  animal  matter  ammonia  is  formed, 
Which,  by  oxidation,  is  converted  into  nitric  acid,  which  then  combines  with 
the  calcium  of  the  lime,  forming  calcium  nitrate.  This  is  dissolved  in  water, 
and  to  the  solution  potassium  carbonate  (or  chloride)  is  added,  when  calcium 
carbonate  (or  chloride)  and  potassium  nitrate  are  formed  : 

Ca(N03)2  +  K2CO3  ==  2KN03  +  CaCO,. 

Large  quantities  of  potassium  nitrate  are  made  also  by  mixing  hot  concen- 
trated solutions  of  sodium  nitrate  and  potassium  chloride,  when,  on  cooling, 
potassium  nitrate  separates  in  crystals,  because  it  is  much  less  soluble  in  cold 
water  than  sodium  nitrate  is.  (See  page  193.) 

NaNO3  +  KC1  =  KNO3  +  NaCl. 

Potassium  nitrate  crystallizes  in  six-sided  prisms ;  it  is  soluble  in 
about  3.8  parts  of  cold,  and  0.4  part  of  boiling  water.  It  has  a  cool- 
ing, saline,  and  pungent  taste,  and  a  neutral  reaction.  When  heated 
with  deoxidizing  agents  or  combustible  substances,  these  are  readily 
oxidized. 

It  is  this  oxidizing  power  which  is  made  use  of  in  the  manufacture 
of  gunpowder — an  intimate  mixture  of  potassium  nitrate,  sulphur, 
and  carbon.  Upon  heating  or  igniting  the  gunpowder,  the  sulphur 
and  carbon  are  oxidized,  a  considerable  quantity  of  various  gases 
(CO,  CO2,  N,  SO2,  etc.)  being  formed,  the  sudden  generation  and 
expansion  of  which  cause  the  explosion. 

Potassium  chlorate,  Potassii  chloras,  KC1O3  =121.68  (Chlorate 
of  potash).  This  salt  may  be  obtained  by  the  action  of  chlorine  on  a 
boiling  solution  of  potassium  hydroxidej  as  explained  on  page  237. 

A  cheaper  process  for  its  manufacture  is  the  action  of  chlorine 


POTASSIUM.  259 

upon  a  boiling  solution  of  potassium  carbonate,  to   which  calcium 
hydroxide  has  been  added  : 

K2C03    +   6Ca(OH)2    +    12C1   ==   2KC1O3   +   OaCO3   +   5CaCl2   +    6H2O. 

Practically  all  potassium  chlorate  is  manufactured  now  by  electrol- 
ysis of  solutions  of  potassium  chloride  under  proper  conditions. 

Potassium  chlorate  crystallizes  in  white  plates  of  a  pearly  lustre ; 
it  is  soluble  in  16.7  parts  of  cold,  and  1.7  parts  of  boiling  water.  It 
is  even  a  stronger  oxidizing  agent  than  potassium  nitrate,  for  which 
reason  care  must  be  taken  in  mixing  it  with  organic  matter  or  other 
deoxidizing  agents,  or  with  strong  acids,  which  will  liberate  chloric 
acid.  When  heated  by  itself,  it  is  decomposed  into  potassium  chloride 
and  oxygen. 

Potassium  sulphate,  Potassii  sulphas,  K2SO4  =  173. 04.  Ob- 
tained by  the  decomposition  of  potassium  chloride,  nitrate,  or  carbo- 
nate, by  sulphuric  acid  : 

2KC1  +  H2SO4  =  2HC1  +  K2SO4; 
K2C03  +  H2S04  =  H20  +  C03  +  K2S04. 

Potassium  sulphate  exists  in  small  quantities  in  plants,  and  in 
nearly  all  animal  tissues  and  fluids,  more  abundantly  in  urine. 

Potassium  hydrogen  sulphate,  bisulphafe,  or  potassium  acid  sulphate,  may  be 
obtained  by  the  action  of  one  molecule  of  potassium  chloride  upon  one  mole- 
cule of  sulphuric  acid : 

KC1  +  H2SO4  =  HC1  -f  KHSO4. 

Potassium  sulphite.  Obtained  by  the  decomposition  of  potassium  carbonate 
by  sulphurous  acid : 

K3CO3  +  H2SOS  =  H2O  +  CO2  +  K2SOS. 

Potassium  hypophosphite,  Potassii  hypophosphis,  KPH2O2  = 
103.39,  may  be  obtained  by  decomposing  a  solution  of  calcium  hypo- 
phosphite  by  potassium  carbonate : 

Ca(PH2O2)2  +  K2CO3  =  2KPH2O2  +  CaCO3. 

The  filtered  solution  is  evaporated  at  a  very  gentle  heat,  stirring 
constantly  from  the  time  it  begins  to  thicken  until  a  dry,  granular 
salt  is  obtained,  which  is  soluble  in  0.5  part  of  cold  and  0.3  part  of 
boiling  water. 

Potassium  iodide,  Potassii  iodidum,  KI  =  164.76,  is  made  by 
the  addition  of  iodine  to  a  solution  of  potassium  hydroxide  until  the 
dark-brown  color  no  longer  disappears  : 

6KOH  +  61  =  5KI  +  KI03  +  3H2O. 


260  METALS  AND   THEIR   COMBINATIONS. 

Iodide  and  iodate  of  potassium  are  formed,  and  may  be  separated 
by  crystallization.  A  better  method,  however,  is  to  boil  to  dryness 
the  liquid  containing  both  salts,  and  to  heat  the  mass  after  having 
mixed  it  with  some  charcoal,  in  a  crucible,  when  the  iodate  is  con- 
verted into  iodide : 

KIO3    +     30    =    KI    +     SCO. 

Experiment  21.  Add  to  a  solution  of  about  3  grammes  of  potassium  hydroxide 
in  about  25  c.c.  of  water  (or  to  the  solution  obtained  by  making  Experiment 
20)  iodine  until  the  brown  color  no  longer  disappears.  (How  much  iodine  will 
be  needed  for  3  grammes  of  KOH?)  Evaporate  the  resulting  solution  (What 
does  this  solution  contain  now  ?)  to  dryness,  mix  the  powdered  mass  with  about 
10  per  cent,  of  powdered  charcoal  and  heat  the  mixture  in  a  crucible  until 
slight  deflagration  has  taken  place.  Dissolve  the  cold  mass  in  hot  water,  filter 
and  set  aside  for  crystallization  ;  if  too  much  water  has  been  used  for  dissolving, 
the  liquid  must  be  concentrated  by  evaporation. 

Potassium  iodide  forms  colorless,  cubical  crystals,  which  are  soluble 
in  0.5  part  of  boiling  and  0.8  part  of  cold  water,  also  soluble  in  12 
parts  of  alcohol,  and  2.5  parts  of  glycerin.  When  heated  it  fuses, 
and  at  a  bright-red  heat  is  volatilized  without  decomposition. 

Potassium  bromide,  Potassii  bromidum,  KBr  =  118.22,  may  be 
obtained  in  a  manner  analogous  to  that  given  for  potassium  iodide, 
by  the  action  of  bromine  upon  potassium  hydroxide,  etc. 

Or  it  may  be  made  by  the  decomposition  of  a  solution  of  ferrous 
bromide  by  potassium  carbonate  : 


Ferrous  carbonate  is  precipitated,  while  potassium  bromide  remains 
in  solution,  from  which  it  is  obtained  by  crystallization. 

Potassium  salts  of  interest,  which  have  not  yet  been  mentioned,  will  be  con- 
sidered under  the  head  of  their  respective  acids.  Some  of  these  salts  are 
potassium  chromate  and  permanganate,  and  the  salts  formed  from  organic 
acids,  such  as  potassium  tartrate,  acetate,  etc. 

Tests  for  potassium. 

(Potassium  chloride,  KC1,  or  nitrate,  KNO3,  may  be  used.) 
1.  To  a  solution  of  any  potassium  salt  add  some  solution  of  chloro- 
platinic  acid.     A  yellow  crystalline  precipitate  of  potassium  chloro- 
platinate  is  obtained  : 

2KN03  +  H2PtCl6  =  K2PtCl6  +  2HN03; 

or        2K-  +  2NQ,'  +  2H«  +  PtCl6"  =  K2PtCl6  +  2H'  +  2NQ/ . 
This  test  is  not  very  delicate,  as  1  part  of  the  precipitate  is  soluble  in 
about  100  parts  of  water.     It  is  much  less  soluble  in  alcohol,  which 
is  usually  added  to  facilitate  precipitation. 


POTASSIUM.  261 

2.  To  a  neutral  or  slightly  acid  solution  of  a  potassium  salt  add  solu- 
tion of  sodium  cobaltic  nitrite:  a  yellow  precipitate  of  potassium  cobaltic 
nitrite,   (KNO2)6.Co2(NO2)6  +  H2O,  is   produced.      (The   reaction  is 
not  influenced  by  the  presence  of  alkaline  earths,  earths,  or  metals  of 
the  iron  group,  but  is  not  suitable  in  case  of  potassium  iodide,  since 
iodine  is  liberated  by  the  nitrous  acid  of  the  cobalt  solution,  and 
interferes  with  the  test.) 

3.  Add  to  a  concentrated  solution  of  a  neutral  potassium  salt  a 
freshly  prepared  strong  solution  of  tartaric  acid :  a  white  precipitate 
of  potassium  acid  tartrate,  KHC4H4O6,  is  slowly  formed.     Addition 
of  alcohol  facilitates  precipitation. 

Tartaric  acid,  H2.C4H4O6,  is  dibasic  and  dissociates  chiefly  into  H* 
and  HC4H4O/  ions.  Potassium  ions,  K',  and  HC4H4O6'  ions  unite 
to  form  the  difficultly  soluble  acid  tartrate ; 

K-  +  NO./  -f  H-  +  HC4H4O6'  =  KHC4H406  +  H'  +  NO,'. 

One  part  of  the  salt  is  soluble  in  about  200  parts  of  water,  but  prac- 
tically insoluble  in  alcohol,  even  when  diluted. 

4.  Potassium  compounds  color  violet  the  flame  of  a  Bunsen  burner 
or  of  alcohol.     The  presence  of  sodium,  which  colors  the  flame  in- 
tensely yellow,  interferes  with  this  test,  as  it  masks  the  violet  caused 
by  potassium.     The  difficulty  may  be  overcome  by  observing  the 
flame  through  a  blue  glass  or  through  a  thin  vessel  filled  with  a  solu- 
tion of  indigo.     The  yellow  light  is  absorbed  by  the  blue  medium, 
while  the  violet  light  passes  through  and  can  be  recognized.1 

With  few  exceptions,  potassium  compounds  are  white,  soluble  in 
water,  and  not  volatile  at  a  low  red  heat.  Of  the  above  tests,  the 


1  The  flame  reaction  for  metals  is  one  of  the  steps  taken  in  qualitative  analysis.  For  this 
purpose  the  platinum  wire  should  be  kept  immersed  in  hydrochloric  acid  in  a  test-tube. 
When  needed,  it  is  cleaned  by  alternately  holding  it  in  the  flame  and  dipping  it  in  the  acid, 
until  no  color  is  given  to  the  flame.  The  salt  best  adapted  for  flame  tests  is  a  chloride ;  hence 
the  substance  to  be  tested  should  be  moistened  in  a  dish  with  hydrochloric  acid  before  intro- 
ducing it  into  the  flame  on  the  loop  of  the  wire.  Chlorides  are  readily  volatilized.  Unless  the 
substance  is  volatile,  there  will  be  110  flame  reaction. 

QUESTIONS. — How  is  potassium  found  in  nature,  and  from  what  sources  is 
the  chief  supply  of  potassium  salts  obtained  ?  What  color  have  the  salts  of  the 
alkali  metals,  and  which  are  insoluble  ?  Mention  two  processes  for  making  potas- 
sium hydroxide,  and  what  are  its  properties?  Show  by  symbols  the  conversion 
of  carbonate  into  bicarbonate  of  potassium.  Explain  the  principle  of  the  man- 
ufacture of  potassium  nitrate,  and  what  is  the  office  of  the  latter  in  gunpowder? 
How  is  potassium  chlorate  made,  and  what  are  its  properties  ?  Give  the  proc- 
esses for  manufacturing  iodide  and  bromide  of  potassium,  both  in  words  and 
symbols.  State  the  composition  of  potassium  sulphate  and  sulphite.  How  can 
they  be  obtained?  Mention  tests  for  potassium  compounds.  How  much  iodine 
is  contained  in  33  grammes  of  potassium  iodide? 


262  METALS  AND   THEIR   COMBINATIONS. 

second  is  the  most  delicate.  Some  other  difficultly  soluble  salts  of 
potassium  arc  the  picrate,  perchlorate  and  fluosilicate.  With  the 
exception  of  the  acid  tartrate  (cream  of  tartar)  and  the  picrate,  the 
other  difficultly  soluble  salts  of  potassium  are  of  a  kind  not  usually  met 
with. 

22.  SODIUM  (NATRIUM). 

Nai-=23  (22.88). 

Occurrence  in  nature.  Sodium  is  found  very  widely  diffused  in 
small  quantities  through  all  soils.  It  occurs  in  large  quantities  in 
combination  with  chlorine,  as  rock-salt,  or  common  salt,  which  forms 
considerable  deposits  in  some  regions,  or  is  dissolved  in  spring  waters, 
and  is  by  them  carried  to  the  rivers,  and  finally  to  the  ocean,  which 
contains  immense  quantities  of  sodium  chloride.  It  is  found,  also, 
as  nitrate,  and  in  double  silicates. 

Sodium  chloride,  Sodii  chloridum,  NaCl  — 58.06  (Common  salt}. 
This  is  the  most  important  of  all  sodium  compounds,  and  also  is  the 
material  from  which  the  other  compounds  are  directly  or  indirectly 
obtained.  Common  table-salt  frequently  contains  small  quantities 
of  calcium  and  magnesium  chlorides,  the  presence  of  which  causes 
absorption  of  moisture,  as  these  compounds  are  hygroscopic,  while 
pure  sodium  chloride  is  not. 

In  the  animal  system,  sodium  chloride  is  found  in  all  parts,  it 
being  of  great  importance  in  aiding  the  absorption  of  albuminoid 
substances  and  the  phenomena  of  osmose;  also  by  furnishing, 
through  decomposition,  the  hydrochloric  acid  of  the  gastric  juice. 

Sodium  chloride  is  soluble  in  2.8  parts  of  cold  water,  and  in  2.5 
parts  of  boiling  water ;  almost  insoluble  in  alcohol ;  it  crystallizes  in 
cubes  and  has  a  neutral  reaction. 

Sodium  hydroxide,  Sodii  hydroxidum,  NaOH  —  39.76  (Caustic 
soda),  may  be  obtained  by  the  processes  mentioned  for  potassium 
hydroxide,  which  compound  it  closely  resembles  in  its  chemical  and 
most  of  its  physical  properties. 

Experiment  22.  Examine  the  consistency  and  lustre  of  sodium  metal  by 
cutting  a  piece  the  size  of  a  pea.  (Do  not  get  water  on  it  while  handling  it. 
Why  ?)  Throw  small  chips  of  the  metal  into  a  little  water  in  a  porcelain  dish. 
When  all  the  metal  has  disappeared,  taste  the  solution  and  test  its  action  on 
red  litmus.  Add  dilute  hydrochloric  acid  to  slight  acid  reaction  and  evaporate 
to  dryness.  Taste  the  residue.  What  is  it  ?  Explain  all  that  took  place  and 
write  reactions. 


SODIUM.  263 

Sodium  peroxide,  Na202.  is  now  extensively  used  as  a  bleaching  and  ox- 
idi/ing  agent.  It  is  a  white  or  yellowish-white  powder,  readily  decomposed  by 
water  into  sodium  hydroxide  and  oxygen;  when  dissolved  in  a  dilute  acid, 
hydrogen  peroxide  is  formed.  It  is  made  by  heating  sodium  in  a  current  of 
oxygen.  When  it  is  brought  in  contact  with  water  or  dilute  acids,  great  care 
must  be  taken  to  have  a  low  temperature,  else  violent  action  will  take  place, 
with  evolution  of  oxygen. 

Sodium  carbonate,  Na2CO3.10H2O  (Washing  soda,  Sal  sodce). 
This  compound  is,  of  all  alkaline  substances,  the  one  manufactured  in 
the  largest  quantities,  being  used  in  the  manufacture  of  many  highly 
important  articles,  as,  for  instance,  soap,  glass,  etc. 

Sodium  carbonate  is  made,  according  to  Leblanc's  process,  from 
the  chloride  by  first  converting  it  into  sulphate  (salt-cake)  by  the 
action  of  sulphuric  acid  : 

2NaCl  +  H2S04  ==  2HC1  +  Na2SO4 

The  escaping  vapors  of  hydrochloric  acid  are  absorbed  in  water, 
and  this  liquid  acid  is  used  largely  in  the  manufacture  of  bleaching- 
powder.  The  sodium  sulphate  is  mixed  with  coal  and  limestone 
(calcium  carbonate)  and  the  mixture  heated  in  reverberatory  furnaces, 
when  decomposition  takes  place,  calcium  sulphide,  sodium  carbonate, 
and  carbonic  oxide  being  formed  : 

Na2SO4  +  40  +  CaCO3  =  CaS  +  Na,CO8  +  4CO 

The  resulting  mass,  known  as  black-ash,  is  washed  with  water, 
which  dissolves  the  sodium  carbonate,  while  calcium  sulphide  enters 
into  combination  with  calcium  oxide,  thus  forming  an  insoluble 
double  compound  of  oxy-sulphide  of  calcium. 

The  liquid  obtained  by  washing  the  black-ash,  when  evaporated 
to  dryness,  yields  crude  sodium  carbonate,  or  " soda  ash" ;  when  this 
is  dissolved  and  crystallized  it  takes  up  ten  molecules  of  water, 
forming  the  ordinary  washing  soda. 

Sodium  carbonate  is  manufactured  also  by  the  so-called  ammonia 
process,  or  the  Solvay  process.  This  depends  on  the  decomposition 
of  sodium  chloride  by  ammonium  bicarbonate  under  pressure,  when 
sodium  bicarbonate  and  ammonium  chloride  are  formed,  thus : 

NaCl  +  NH4HCO3  =  NH4C1  +  NaHCO3. 

• 

The  sodium  acid  carbonate  thus  obtained  is  converted  into  carbo- 
nate by  heating : 

2NaHCO,  ==  Na2CO3  +  H2O  +  CO2. 

The  carbon  dioxide  obtained  by  this  action  is  caused  to  act  upon 
ammonia,  liberated  from  the  ammonium  chloride,  obtained  as  one  of 


264  METALS  AND   THEIR  COMBINATIONS. 

the  products  in  the  first  reaction.  Ammonium  bicarbonate  is  thus 
regenerated  and  used  in  a  subsequent  operation  for  the  decomposition 
of  common  salt. 

Sodium  carbonate  has  strong  alkaline  properties ;  it  is  soluble  in 
1.6  parts  of  cold  water,  and  in  much  less  water  at  higher  temper- 
atures ;  the  crystals  lose  water  on  exposure  to  the  air,  falling  into  a 
white  powder;  heat  facilitates  the  expulsion  of  the  water  of  crys- 
tallization, and  is  applied  in  making  the  monohydrated  sodium  car- 
bonate, Sodii  carbonas  monohydras,  Na2CO3.H2O  =  123.19,  which 
should  contain  about  85  per  cent,  of  anhydrous  sodium  carbonate. 

Sodium  bicarbonate,  Sodii  bicarbonas,  NaHCO3  =  83.43  (Bak- 
ing-soda). Obtained,  as  stated  in  the  previous  paragraph,  by  the 
ammonia-soda  process.  It  can  also  be  made  by  passing  carbon 
dioxide  over  monohydrated  sodium  carbonate. 

Na,CO3.H2O     +     CO2    =  =    2NaHCO3. 

It  is  a  white  powder,  having  a  cooling,  mildly  saline  taste,  and  a 
slightly  alkaline  reaction.  Soluble  in  12  parts  of  cold  water  and 
insoluble  in  alcohol.  It  is  decomposed  by  heat  or  by  hot  water  into 
sodium  carbonate,  water,  and  carbon  dioxide. 

Sodium  bicarbonate  is  a  constituent  of  the  various  baking-powders,  the  action 
of  which  depends  on  the  gradual  liberation  of  carbon  dioxide  in  the  dough. 
This  is  brought  about  through  a  second  constituent,  generally  an  acid  salt  such 
as  potassium  bitartrate  or  calcium  acid  phosphate,  which  decomposes  the 
bicarbonate. 

Sodium  sulphate,  Sodii  sulphas,  Na2SO4lOH2O  =  319.91  (Glau- 
ber's  salt).  Made,  as  mentioned  above,  by  the  action  of  sulphuric  acid 
on  sodium  chloride,  dissolving  the  salt  thus  obtained  in  water,  and  crys- 
tallizing. Large,  colorless,  transparent  crystals,  rapidly  efflorescing 
on  exposure  to  air.  Soluble  in  2.8  parts  of  water  at  15°  C.  (59°  F.). 
in  0.25  part  at  34°  C.  (93°  F.),  and  in  0.47  part  of  boiling  water. 

Experiment  23.  Dissolve  about  10  grammes  of  crystallized  sodium  carbonate 
in  10  c.c.  of  hot  water,  add  to  this  solution  dilute  sulphuric  acid  until  all  effer- 
vescence ceases  and  the  reaction  on  litmus-paper  is  exactly  neutral.  Evaporate 
to  about  20  c.c.,  and  set  aside  for  crystallization.  Explain  the  action  taking 
place,  and  state  how  much  H2S04,  and  how  much  of  the  diluted  sulphuric 
acid,  U.  S.  P.,  are  needed  for  the  decomposition  of  10  grammes  of  crystallized 
sodium  carbonate. 

Sodium  sulphite,  Sodii  sulphis,  Na2SO3.7H2O  --  =  25O.39. 
Sodium  bisulphite,  Sodii  bisulphis,  NaHSO3  =  1O3.35.  By 


SODIUM.  265 

saturating  a  cold  solution  of  sodium  carbonate  with  sulphur  dioxide, 
sodium  bisulphite  is  formed,  and  separates  in  opaque  crystals : 

Na-jCOg  -f  2SO2  +  H2O  =  2NaHSO3  -f  CO2. 

If  to  the  sodium  bisulphite  thus  obtained  a  quantity  of  sodium  car- 
bonate be  added,  equal  to  that  first  employed,  the  normal  salt  is  formed : 
2NaHSO3  -(-  Na.2CO3  =  2NaaSOs  +  H2O  +  CO2. 

Sodium  thiosulphate,  Sodium  hyposulphite,  Sodii  thiosul- 
phas,  Na2S2O3.5H2O  =  246.46.  Made  by  digesting  a  solution  of 
sodium  sulphite  with  powdered  sulphur,  when  combination  slowly 
takes  place  : 

Na2S03     +     S     :        Na2SA- 

It  is  used  under  the  name  of  "  h^po  "  in  photography  to  dissolve 
chloride,  bromide,  or  iodide  of  silver. 

Sodium  phosphate,  Sodii  phosphas,  Na2HPO4.12H2O  —  355.61, 
is  made  from  calcium  phosphate  by  the  action  of  sulphuric  acid,  which 
removes  two-thirds  of  the  calcium,  forming  calcium  sulphate,  while 
acid  phosphate  of  calcium  is  formed  and  remains  in  solution  : 

Ca3(PO4)2  +  2H2S04  =  2CaSO4  -f  CaH4(PO4)2. 

The  solution  is  filtered  and  sodium  carbonate  added,  when  calcium 
phosphate  is  precipitated,  phosphate  of  sodium,  carbon  dioxide,  and 
water  being  formed  : 

CaH4(P04)2  +  Na2CO8  =  CaHPO4  -f  H2O  +  CO2  -f  N^HPO,. 

The  filtered  and  evaporated  solution  yields  crystals  of  sodium 
phosphate,  which  have  a  slightly  alkaline  reaction  to  litmus,  but  not 
to  phenol-phthalein. 

By  exposure  of  the  crystallized  sodium  phosphate  to  warm  air  its  water  of 
crystallization  is  expelled  and  the  dry  salt  is  Exsiccated  sodium  phosphate, 
Sodii  phosphas  exsiccatus.  This  salt,  when  mixed  with  the  proper  quantities 
of  sodium  bicarbonate  and  tartaric  and  citric  acids,  is  official  under  the  name 
of  Effervescent  sodium  phosphate,  Sodii  phosphas  effervescens. 

Experiment  24.  Mix  thoroughly  30  grammes  of  bone-ash  with  10  c.c.  of 
sulphuric  acid,  let  stand  for  some  hours,  add  20  c.c.  of  water,  and  again  set 
aside  for  some  hours.  Mix  with  40  c.c.  of  water,  heat  to  the  boiling-point,  and 
filter.  The  residue  on  the  filter  is  chiefly  calcium  sulphate.  To  the  hot  filtrate 
of  calcium  acid  phosphate  add  concentrated  solution  of  sodium  carbonate  until 
a  precipitate  ceases  to  form  and  the  liquid  is  faintly  alkaline,  filter,  evaporate, 
and  let  crystallize. 

Sodium  pyrophosphate,  Sodii  pyrophosphas,  Na4P2O7.lOH2O  = 
443.O2.  When  exsiccated  sodium  phosphate  is  heated  to  a  low  red 


266  METALS  AND   THEIR  COMBINATIONS. 

heat  it  loses  water,  and  is  converted  into  pyrophosphate,  which,  dis- 
solved in  hot  water  and  crystallized,  forms  the  official  salt.  The 
chemical  change  taking  place  is  this  : 

2(Na2HP04)  Na4P207     +     H2O. 

The  normal  sodium  phosphate,  Na3PO4,  is  known  also,  but  it  is  not  a  very 
stable  compound,  being  acted  upon  even  by  the  moisture  and  carbon  dioxide 
of  the  air,  with  the  formation  of  sodium  carbonate  and  disodium  hydrogen 
phosphate,  thus  : 

H20  +  C02  = 


Sodium  nitrate,  Sodii  nitras,  NaNO3=  84.45  (Chile  saltpeter, 
Cubic  niter).  Found  in  nature,  and  is  purified  by  crystallization. 
The  crystals  are  transparent,  deliquescent,  and  readily  soluble. 

Sodium  nitrite,  Sodii  nitris,  NaNO2  =  68.57,  is  formed  by  heating  the  nitrate 
to  a  sufficiently  high  temperature  to  expel  one-third  of  the  oxygen  ;  or,  better, 
by  treating  the  fused  nitrate  with  metallic  lead,  which  latter  is  converted  into 
oxide.  The  sodium  nitrite  which  is  formed  is  dissolved  and  purified  by  crystal- 
lization. 

Sodium  borate,  Sodii  boras,  Na2B4O7.lOH2O  =  379.32  (Borax). 
This  salt  occurs  in  Clear  Lake,  Nevada,  and  in  several  lakes  in  Asia. 
It  is  manufactured  by  adding  sodium  carbonate  to  the  boric  acid 
found  in  Tuscany,  Italy.  It  forms  colorless,  transparent  crystals, 
but  is  sold  mostly  in  the  form  of  a  white  powder.  It  is  slightly 
efflorescent,  is  soluble  in  16  parts  of  cold,  and  in  0.5  part  of  boiling 
water  ;  insoluble  in  alcohol,  but  soluble  in  one  part  of  glycerin  at 
80°  C.  (176°  F.).  When  heated,  borax  puffs  up,  loses  water  of 
crystallization,  and  at  red  heat  it  melts,  forming  a  colorless  liquid 
which,  on  cooling,  solidifies  to  a  transparent  mass,  known  as  fused 
borax,  or  borax  glass.  Molten  borax  has  the  power  to  combine  with 
metallic  oxides,  forming  double  borates,  some  of  which  have  a  char- 
acteristic color,  for  which  reason  borax  is  used  in  blow-pipe  analysis. 
Borax  has  antiseptic  properties,  preventing  the  decomposition  of  some 
organic  substances. 

A  solution  of  borax  is  alkaline  and  has  no  action  on  carbonates  or  bicarbon- 
ates,  but  if  an  equal  volume  of  glycerin  is  added  to  the  solution,  it  becomes 
strongly  acid  and  decomposes  carbonates  and  bicarbonates  with  effervescence. 
This  behavior  has  an  important  bearing  in  prescription  writing.  On  diluting 
the  glycerin  mixture  strongly  with  water,  the  alkaline  reaction  returns. 

Other  sodium  salts  which  are  official  are  sodium  hypophosphite, 
NaPH2O2  +  H2O;  bromide,  NaBr;  iodide,  Nal  ;  chlorate,  NaClO3. 


SODIUM.  267 

These  salts  may  be  obtained  by  processes  analogous  to  those  given 
for  the  corresponding  potassium  compounds. 

Sodium  compounds  are  nearly  all  white  and  are  not  volatile  at  or 
below  a  red  heat. 

Tests  for  sodium. 

(Sodium  chloride,  NaCl,  may  be  used.) 

1.  As  all  salts  of  sodium  are  soluble  in  water,  we  cannot  precipi- 
tate this  metal  in  the  form  of  a  compound  by  any  of  the  common 
reagents.      (Potassium    antimoniate  precipitates  neutral  solution  of 
sodium  salts,  but  this  test  is  not  reliable.) 

2.  The  chief  reaction  for  sodium  is  the  flame-test,  compounds  of 
sodium  imparting  to  a  colorless  flame  a  yellow  color,  which   is  very 
intense.     A  crystal  of  potassium  dichromate  appears  colorless,  and  a 
paper  coated  with  red  mercuric  iodide  appears  white  when  illuminated 
by  the  yellow  sodium  flame.     (The  spectroscope  shows  a  characteristic 
yellow  line.) 

As  practically  all  substances  contain  a  trace  of  some  sodium  com- 
pound, and  give  a  momentary  sodium  flame,  the  yellow  flame  can  only 
be  used  to  judge  the  presence  of  an  actual  sodium  compound  when 
it  persists  for  a  long  time. 

Lithium,  Li  =  6.98.  Found  in  nature  in  combination  with  silicic  acid  in 
a  few  rare  minerals  or  as  a  chloride  in  some  spring  waters.  Of  inorganic 
salts,  lithium  bromide  and  carbonate  are  official.  Hydroxide,  carbonate,  and 
phosphate  of  lithium  are  much  less  soluble  than  the  corresponding  com- 
pounds of  potassium  and  sodium.  Sodium  phosphate  added  to  a  strong  solu- 
tion of  a  lithium  salt  produces,  on  boiling,  a  white  precipitate  of  lithium 
phosphate,  Li3PO4.  Lithium  compounds  color  the  flame  a  beautiful  crimson 
or  carmine-red. 

LiOH  is  soluble  in  14.5  parts  of  water  at  20°  C.,  Li2CO3  in  75  parts  at  20°  C., 
and  140  parts  of  boiling  water,  Li3PO4  in  2540  parts  of  plain  water  and  3920 
parts  of  ammoniacal  water. 

Caesium,  Cs,  and  Rubidium,  Rb,  occur  widely  distributed,  but  only  in 
small  quantities,  and  generally  in  company  with  potassium,  which  they  resem- 

QUESTIONS. — What  is  the  composition  of  common  salt ;  how  is  it  found  in 
nature,  and  what  is  it  used  for?  Describe  Leblanc's  and  the  Solvay  process 
for  manufacturing  sodium  carbonate  on  a  large  scale.  How  much  water  is  in 
100  pounds  of  the  crystallized  sodium  carbonate  ?  What  is  Glauber  salt,  and 
how  is  it  made  ?  State  the  composition  of  disodium  hydrogen  phosphate,  and 
how  is  it  prepared  from  calcium  phosphate?  What  difference  exists  between 
sodium  carbonate  and  bicarbonate  both  in  regard  to  physical  and  chemical 
properties?  Give  the  composition  of  sodium  thiosulphate;  what  is  it  used  for? 
Which  sodium  salts  are.  soluble,  and  which  are  insoluble?  How  does  sodium 
and  how  does  lithium  color  the  flame?  Which  lithium  salts  are  official? 


268  METALS  AND   THEIR  COMBINATIONS. 

ble  closely.  Kubidium  occurs  in  carnallite  of  the  Stassfurt  beds,  and  is  obtained 
as  rubidium  alum,  from  the  mother-liquors  after  the  potassium  chloride  is 
crystallized  out.  Csesium  takes  fire  in  air  at  the  ordinary  temperature,  and  it 
is  the  most  electropositive  of  all  metals.  Kubidium  takes  fire  in  air  and  decom- 
poses water  with  greater  energy  than  does  potassium,  the  hydroxide  formed, 
Rb(OH),  having  even  stronger  basic  properties  than  potassium  hydroxide. 
Both  rubidium  and  caesium  have  a  marked  power  of  forming  double  salts.  All 
the  salts  are  white  and  soluble  in  water.  Probably  the  one  most  often  used 
medicinally  is  ccesium-rubidium-ammonium  bromide,  (CsEb)Br2.3NH4Br.  Rubid- 
ium bromide,  RbBr,  and  iodide,  Rbl,  have  been  recommended  as  substitutes  for 
the  corresponding  potassium  salts.  Cesium  bromide,  CsBr,  has  also  been  used. 

23.   AMMONIUM. 
NH^IS  (17.93). 

General  remarks.  The  salts  of  ammonium  show  so  much  resem- 
blance, both  in  their  physical  and  chemical  properties,  to  those  of  the 
alkali-metals,  that  they  may  be  studied  most  conveniently  at  this 
place. 

The  compound  radical  NH4  acts  in  these  ammonium  salts  very 
much  like  one  atom  of  an  alkali-metal,  and,  therefore,  frequently  has 
been  looked  upon  as  a  compound  metal.  The  physical  metallic  prop- 
erties (lustre,  etc.)  of  ammonium  cannot  be  fully  demonstrated,  as  it 
is  not  capable  of  existing  in  a  separate  or  free  state.  There  is  known, 
however,  an  alloy  of  ammonium  and  mercury,  which  may  be  obtained 
by  dissolving  potassium  in  mercury,  and  adding  to  the  potassium- 
amalgam  thus  formed,  a  strong  solution  of  ammonium  chloride,  when 
potassium  chloride  and  ammonium-amalgam  are  formed.  The  latter 
is  a  soft,  spongy,  metallic-looking  substance,  which  readily  decomposes 
into  mercury,  ammonia,  and  hydrogen  : 

HgK  +  NH4C1  =  KC1  +  NH4Hg; 
NH4Hg  =  NH3  +  H  +  Hg. 

The  source  of  all  ammonium  compounds  is  ammonia  NH3,  or  am- 
monium hydroxide,  NH4OH,  both  of  which  have  been  considered 
heretofore. 

A  solution  of  ammonia  has  much  weaker  basic  properties  than  a  solution 
of  sodium  or  potassium  hydroxide  has.  In  a  normal  solution  (about  1.7  per 
cent.)  only  about  0.4  per  cent,  of  the  ammonia  molecules  are  dissociated  into 
NH4-  and  (OH)/  ions.  There  is  much  free  NH3,  besides  the  NH4OH  which 
results  from  union  of  NH3  with  water.  It  is  only  the  ionized  portion  of  the 
NH4OH  which  shows  basic  properties. 

The  ionic  equation  for  the  neutralization  of  ammonia  water  with  an  acid  is 
this: 

NH4-,-f  OH'  +  H-  +  d'  ->  NH4-  +  Cl'  +  H2O. 
As  fast  as  (OH)7  and  H'  ions  unite  to  form  water,  more  NH4OH  dissociates 


AMMONIUM.  269 

and  more  NH3  unites  with  water  to  form  NH4OH  until  the  reaction  is  com- 
plete.    All  ammonium  salts  are  highly  dissociated  in  dilute  solutions. 

The  reverse  of  the  above  action,  namely,  the  liberation  of  ammonia  from  its 
salts  by  an  alkali,  is  discussed  from  the  ionic  point  of  view  on  page  194. 

Ammonium  chloride,  Ammonii  chloridum,  NH4C1~  53.11  (Sal- 
ammoniac).  Obtained  by  saturating  the  "ammoniacal  liquor"  of  the 
gas-works  with  hydrochloric  acid,  evaporating  to  dryness,  and  puri- 
fying the  crude  article  by  sublimation. 

Pure  ammonium  chloride  either  is  a  white,  crystalline  powder,  or 
occurs  in  the  form  of  long,  fibrous  crystals,  which  are  tough  and 
flexible ;  it  has  a  cooling,  saline  taste ;  is  soluble  in  2  parts  of  cold, 
and  in  1  part  of  boiling  water;  and,  like  all  ammonium  compounds, 
is  completely  volatilized  by  heat. 

Carbamic  acid,  CO.NH2.OH.  This  acid  may  be  looked  upon  as  carbonic 
acid,  CO.(OH)2,  in  which  one  of  the  hydroxyl  groups  is  replaced  by  NH^  The 
ammonium  salt  of  this  acid,  CO.NH.2.ONH4,  is  formed  when  dry  ammonia  gas 
and  dry  carbon  dioxide  are  brought  together,  direct  combination  taking  place, 

thus: 

NH2 
CO2  +  2NH3  =  CO( 

\ONH4 

Ammonium  carbonate,  Ammonii  carbonas,  NH4HCO3.NH4 
NH2CO2  =  156. Ol  (Ammonium  sesquicarbonate,  sal  volatile,  Preston 
salt).  Commercial  ammonium  carbonate  is  not  the  normal  salt,  but, 
as  shown  by  the  above  formula,  a  combination  of  acid  ammonium 
carbonate  with  ammonium  carbamate.  It  is  obtained  by  sublimation 
of  a  mixture  of  ammonium  chloride  and  calcium  carbonate,  when 
calcium  chloride  is  formed,  ammonia  gas  and  water  escape,  and  am- 
monium carbonate  condenses  in  the  cooler  part  of  the  apparatus : 

2CaC03  +  4NH4C1  =  NH4HCO3  NH4NH2CO2  +  2CaCl2  +  H2O  +  NH3. 

Ammonium  carbonate  thus  obtained  forms  white,  translucent  masses,  losing 
both  ammonia  and  carbon  dioxide  on  exposure  to  the  air,  becoming  opaque, 
and  finally  converted  into  a  white  powder  of  acid  ammonium  carbonate. 

NH4HCO3  NH4NH2CO2  =  NH4HCO3  +  2NH3  -f  CO2. 

When  commercial  ammonium  carbonate  is  dissolved  in  water  the  carbamate 
unites  with  one  molecule  of  water,  forming  normal  ammonium  carbonate. 

NH4NH2CO2  +  H2O  =  (NH4)2C08. 

A  solution  of  the  common  ammonium  carbonate  in  water  is,  consequently,  a 
liquid  containing  both  acid  and  normal  carbonate  of  ammonium ;  by  the  addi- 
tion of  some  ammonia  water  the  acid  carbonate  is  converted  into  the  normal 
salt.  The  solution  thus  obtained  is  used  frequently  as  a  reagent. 

The  Aromatic  spirit  of  ammonia  is  a  solution  of  normal  ammonium  carbonate 
in  diluted  alcohol  to  which  some  essential  oils  have  been  added. 


270  METALS  AND   THEIR  COMBINATIONS. 

Ammonium  sulphate,  (NH4)2SO4,  Ammonium  nitrate,  NH4NO3, 
and  Ammonium  phosphate,  (NH4)2HPO4,  may  be  obtained  by  the 
addition  of  the  respective  acids  to  ammonia  water  or  ammonium 
carbonate  : 

H2S04  +  2NH4OH  =  (NH4)2S04  -f  2H2O. 
HNO3  +  NH4OH  =  NH4NO3  -f  H2O. 
H3P04  +  2NH4OH  =  (NH4)2HP04  +  2H2O. 
H2S04  -f  (NH4)2C03  =  (NH4)2S04  +  H2O  +  COa. 

Ammonium  iodide,  Ammonii  iodidum,  NH4I,  and  Ammonium 
bromide,  Ammonii  bromidum,  NH4Br,  may  be  obtained  by  mixing 
together  strong  solutions  of  potassium  iodide  (or  bromide)  and  am- 
monium sulphate,  and  adding  alcohol,  which  precipitates  the  potas- 
sium sulphate  formed  ;  by  evaporation  of  the  solution  the  ammonium 
iodide  (or  bromide)  is  obtained  : 

2KI     +  (NH4)2SO4  =  2NH4I     -f  K2SO4; 
2KBr  +  (NH4)2S04  =  2NH4Br 


Another  mode  of  preparing  these  compounds  is  by  the  decomposi- 
tion of  ferrous  bromide  (or  iodide)  by  ammonium  hydroxide  : 
FeBr2  +  2NH4OH  =  2NH4Br  +  Fe(OH)2. 

Ammonium  iodide  is  the  principal  constituent  of  the  Decolorized 
tincture  of  iodine. 

Ammonium  hydrogen  sulphide,  NH4SH  (Ammonium  hydro- 
sulphide,  Ammonium  sulphydrate).  Obtained  by  passing  hydrogen 
sulphide  through  ammonia  water  until  this  is  saturated  : 

H2S  +  NH4OH  =  NH4SH  4-  H2O. 

The  solution  thus  obtained  is,  when  recently  prepared,  a  colorless 
liquid,  having  the  odor  of  both  ammonia  and  of  hydrogen  sulphide  ; 
when  exposed  to  the  air  it  soon  assumes  a  yellow  color.  This  behavior 
is  characteristic  of  the  soluble  hydrosulphides  in  general,  and  is  due 
to  the  liberation  of  sulphur  by  oxidation,  thus  : 

NH4SH  +  O  =  NH4OH  +  S. 

The  sulphur  combines  with  undecomposed  hydrosulphide,  forming 
polysulphides,  which  are  yellow.  The  normal  sulphide,  (NH4)2S,  can 
be  obtained  in  the  solid  state,  but  it  quickly  loses  half  of  its  ammonia 
and  forms  hydrosulphide.  In  solution  it  is  almost  completely  hydro- 
lyzed,  thus  : 

(NH4)2S  +  H20  ^±  NH4OH  +  NH4SH. 
A  mixture  corresponding  to  the  normal  sulphide  is  obtained  by  add- 


AMMONIUM.  271 

ing  to  a  solution  of  the  hydrosulphide,  prepared  as  above,  an  equiva- 
lent amount  of  ammonia  water. 

These  solutions  can  easily  be  freed  from  the  sulphide  by  boiling.  Both  sub- 
stances, the  ammonium  hydrogen  sulphide  and  ammonium  sulphide,  are  valu- 
able reagents,  frequently  used  for  precipitation  of  certain  heavy  metals,  or  for 
dissolving  certain  metallic  sulphides.  (See  under  Hydrogen  Sulphide.). 

Tests  for  ammonium  compounds. 

(Ammonium  chloride,  NH4C1,  may  be  used.) 

1.  Ammonium  salts  give  the  same  form  of  precipitates  as  potas- 
sium with  solution  of  platinic  chloride,  sodium  cobaltic  nitrite,  and 
tartaric  acid  (see  tests  for  potassium). 

2.  All  compounds  of  ammonium  are  volatilized  below  or  at  a  low 
red  heat,  either  with  or  without  decomposition  (see  preparation  of 
nitrogen  and  nitrogen   monoxide  in  chapter  on  Nitrogen).     If  the 
acid  constituent  of  the  salt  is  volatile  and  not  decomposed  by  heat, 
the  salt  volatilizes  without  decomposition. 

Heat  with  a  small  flame  a  little  ammonium  chloride  in  a  covered 
porcelain  crucible.  The  salt  sublimes  upon  the  sides  and  cover  of 
the  crucible. 

3.  The  best  test  and  one  which  is  sufficient  for  recognition  of  any 
ammonium  compound  is  to  heat  a  mixture  of  it  and  slaked  lime  or 
strong  alkali  in  a  tube.     Ammonia  gas  is  liberated,  which  may  be 
recognized  by  its  odor  and  action  on  red  litmus-paper,  and  by  causing 
dense  white  fumes  when  a  rod,  moistened  with  strong  hydrochloric 
acid,  is  held  in  the  mouth  of  the  tube. 

All  commonly  occurring  ammonium  salts  are  colorless,  soluble  in 
water,  and  odorless,  with  the  exception  of  the  carbonate  and  sulphide. 
Traces  of  ammonium  compounds  are  detected  by  Nessler's 

QUESTIONS. — What  is  ammonium,  and  why  is  it  classed  with  the  alkali- 
metals?  Is  ammonium  known  in  a  separate  state?  What  is  ammonium- 
amalgam,  how  is  it  obtained,  and  what  are  its  properties?  What  is  the  source 
of  ammonium  compounds?  State  the  composition,  mode  of  preparation,  and 
properties  of  sal  ammoniac.  How  is  ammonium  carbonate  manufactured,  and 
what  difference  exists  between  the  solid  article  and  its  solution  ?  State  the 
composition  of  ammonium  sulphide  and  of  ammonium  hydrogen  sulphide ; 
how  are  they  made,  and  what  are  they  used  for?  By  what  process  may  ammo- 
nium sulphate,  nitrate,  and  phosphate  be  obtained  from  ammonium  hydroxide 
or  ammonium  carbonate,  and  what  chemical  change  takes  place  ?  How  does 
heat  act  upon  ammonium  compounds?  Give  analytical  reactions  for  ammo- 
nium salts. 


272 


METALS  'AND   THEIR   COMBINATIONS. 


solution   (see   Index),  which   causes   a  reddish-brown   precipitate  or 
coloration.     (See  under  Water  Analysis,  end  of  chapter  38.) 

Summary  of  analytical  characters  of  the  alkali-metals. 


Potassium. 

/Sodium. 

Lithium. 

Ammonium. 

Sodium  cobaltic  nitrite  .     . 
Platinic  chloride  .... 
Sodium  bitartrate     .     .     . 
Sodium  phosphate    .     .     . 

Sodium  hydroxide    .    .     . 
Action  of  heat     .... 

Yellow  pre- 
cipitate. 
Yellow  pre- 
cipitate. 
White  preci- 
pitate. 

Yellow  pre- 
cipitate. 
Yellow  pre- 
cipitate. 
White  preci- 
pitate. 

White  preci- 
pitate in  cone, 
solution  on 
boiling. 

Ammonia 
gas. 
Volatile. 

Fusible. 
Violet. 

Fusible. 
Yellow. 

Fusible. 
Crimson. 

24.  MAGNESIUM. 
Mg11  =  24.18. 

General  remarks.  Magnesium  occupies  a  position  intermediate 
between  the  alkali  metals  and  the  alkaline  earths.  To  some  extent 
it  resembles  also  the  heavy  metal  zinc,  with  which  it  has  in  common 
the  volatility  of  the  chloride,  the  solubility  of  the  sulphate,  and  the 
isomorphism  of  several  of  its  compounds  with  the  analogously  con- 
stituted compounds  of  zinc. 

Occurrence  in  nature.  Magnesium  is  widely  diffused  in  nature, 
and  several  of  its  compounds  are  found  in  large  quantities.  It  occurs 
as  chloride  and  sulphate  in  many  spring  waters  and  in  the  salt-mines 
at  Stassfurt;  as  carbonate  in  the  mineral  magnesite;  as  double  car- 
bonate of  magnesium  and  calcium  in  the  mineral  dolomite  (magnesian 
limestone),  which  forms  entire  mountains ;  as  silicate  of  magnesium 
in  the  minerals  serpentine,  meerschaum,  tale,  asbestos,  soapstone,  etc. 

Metallic  magnesium  may  be  obtained  by  the  decomposition  of 
magnesium  chloride  by  sodium  ;  but  is  now  made  in  large  quantities 
by  electrolysis  of  the  molten  double  chloride  of  magnesium  and 
potassium,  MgCl2.KCl.  The  furnace  used  for  the  operation  is  shown 
in  Fig.  31,  page  80. 

Magnesium  is  an  almost  silver-white  metal,  losing  its  lustre  rap- 
idly in  moist  air  by  oxidation  of  the  surface.  It  decomposes  hot 


MAGNESIUM.  273 

water  with  liberation  of  hydrogen ;  and  when  heated  to  a  red 
heat  burns  with  a  brilliant  bluish-white  light,  which  is  extensively 
used  for  photographic  purposes. 

Magnesium  carbonate,  Magnesii  carbonas.  Approximately : 
(MgC03)4.Mg(OH)2.5H,0  ==  482.26  (Magnesia  alba).  The  normal 
magnesium  carbonate,  MgCO3,  is  found  in  nature,  but  the  official 
preparation  contains  carbonate,  hydroxide,  and  water.  It  is  ob- 
tained by  boiling  a  solution  of  magnesium  sulphate  with  solution 
of  sodium  carbonate,  when  the  carbonate  is  precipitated,  some  carbon 
dioxide  evolved,  and  sodium  sulphate  remains  in  solution: 

5MgSO4  +  SN^COg  +  6H2O  ==  (MgCO3)4  Mg(OH)2  5H2O  +  5Na2SO4  +  CO3. 

By  filtering,  washing,  and  drying  the  precipitate,  it  is  obtained  in 
the  form  of  a  white,  light  powder. 

Experiment  25.  Dissolve  10  grammes  of  magnesium  sulphate  in  hot  water 
and  add  a  concentrated  solution  of  sodium  carbonate  until  no  more  precipitate 
is  formed.  Collect  the  precipitated  magnesium  carbonate  on  a  filter  and  dry  it 
at  a  low  temperature.  (How  much  crystallized  sodium  carbonate  is  needed 
for  the  decomposition  of  10  grammes  of  crystallized  magnesium  sulphate?) 
Notice  that  the  dried  precipitate  evolves  carbon  dioxide  when  heated  with 
acids. 

Magnesium  oxide,  Mag-nesii  oxidum,  MgO  —  40.O6  (Calcined 
magnesia),  is  obtained  by  heating  light  magnesium  carbonate  in  a 
crucible  to  a  full  red  heat,  when  all  carbon  dioxide  and  water  are 
expelled : 

(MgC03)4.Mg(OH)2.5H2O  =  5MgO  -f  4CO2  +  6H2O. 

It  is  a  very  light,  amorphous,  white,  almost  tasteless  powder,  which 
absorbs  moisture  and  carbon  dioxide  gradually  from  the  air;  in  con- 
tact with  water  it  forms  the  hydroxide  Mg(OH)2,  which  is  almost 
insoluble  in  water,  requiring  of  the  latter  over  50,000  parts  for  solu- 
tion. Milk  of  magnesia  is  the  hydroxide  suspended  in  water  (1  part 
in  about  15). 

Heavy  magnesium  oxide,  magnesii  oxidum  ponderosum,  differs  from  the  com- 
mon or  light  magnesia,  not  in  its  chemical  composition,  but  merely  in  its 
physical  condition,  being  denser  and  heavier. 

Experiment  26.  Place  1  gramme  of  magnesium  carbonate,  obtained  in  per- 
forming Experiment  25,  into  a  weighed  crucible  and  heat  to  redness,  or  until 
by  further  heating  no  more  loss  in  weight  ensues.  Treat  the  residue  with 
dilute  hydrochloric  acid  and  notice  that  no  evolution  of  carbon  dioxide  takes 
place.  What  is  the  calculated  loss  in  weight  of  magnesium  carbonate  when 
converted  into  oxide,  and  how  does  this  correspond  with  the  actual  loss  deter- 
mined by  the  experiment? 
18 


274  NON-METALS  AND   THEIR   COMBINATIONS. 

Magnesium  sulphate,  Magnesii  sulphas,  MgSO4.7H2O  =  244.69 
(Epsom  salt),  is  obtained  from  spring  waters,  from  the  mineral 
Kieserite,  MgSOrH2O,  and  by  decomposition  of  the  native  carbonate 
by  sulphuric  acid : 

MgC03  +  H2SO4  =  MgS04  +  C02  +  H2O. 

It  forms  colorless  crystals,  which  have  a  cooling,  saline,  and  bitter 
taste,  a  neutral  reaction,  and  are  easily  soluble  in  water. 

Effervescent  magnesium  sulphate,  Magnesii  sulphas  efferves- 
cens,  is  a  granular  mixture  of  magnesium  sulphate,  sodium  bicarbonate,  tar- 
taric  and  citric  acids,  in  proper  proportions.  It  contains  what  is  equal  to  50 
per  cent,  of  crystallized  magnesium  sulphate,  and,  like  all  effervescent  salts, 
gives  off  carbonic  acid  when  dissolved,  which  makes  it  more  palatable. 

Magnesium  nitride,  Mg3N2,  is  obtained  as  a  yellow,  porous  mass  by 
heating  magnesium  to  red  heat  in  nitrogen.  With  water  it  forms  magnesium 
hydroxide  and  ammonia,  thus : 

Mg3N2    +    6H20    =    3Mg(OH)2    +    2NH3, 

Remarks  on  tests  for  metals.  Many  of  the  tests  for  magnesium 
and  the  metals  to  follow  have  already  been  before  us  when  discuss- 
ing the  acids.  They  involve  reactions  of  double  decomposition,  re- 
sulting in  the  formation  of  an  insoluble  product.  The  solubilities  of 
the  different  classes  of  salts,  such  as  chlorides,  carbonates,  sulphates, 
etc.,  have  been  stated  under  the  various  acids,  and  the  student,  by 
keeping  these  facts  in  mind,  will  be  able  to  anticipate  many  of  the 
tests  enumerated  under  the  metals.  Some  of  these  are  not  distinctive 
at  all,  but  simply  corroborative,  because  two  or  more  metals  may  re- 
spond to  the  same  test.  For  example,  to  obtain  a  white  precipitate 
on  adding  a  solution  of  sodium  carbonate  or  phosphate  to  a  solution 
of  a  substance  is  no  more  a  test  for  magnesium  than  for  calcium, 
strontium,  barium,  or  any  other  metal  whose  carbonate  or  phosphate  is 
white  and  insoluble  in  water.  In  cases  where  distinctive  tests  are 
lacking,  a  systematic  procedure  of  elimination  is  followed.  This  is 
known  as  qualitative  analysis. 

The  solubilities  of  the  classes  of  salts  and  the  different  methods 
of  producing  salts  have  been  mentioned,  and  something  has  been 
said  in  this  respect  about  the  two  classes  of  compounds  of  metals 
known  as  oxides  and  hydroxides.  In  regard  to  solubility  in  water, 
the  oxides  and  hydroxides  are  very  much  alike :  that  is,  if  a  hydrox- 
ide is  soluble,  the  corresponding  oxide  is  also  soluble,  and  vice  versa. 
The  hydroxides  of  the  common  metals  that  are  soluble  in  water  are 
those  of  potassium,  sodium,  lithium,  barium,  strontium,  and  the  hypo- 


M AGNES  fUM.  275 

thetical  metal,  ammonium.  Calcium  hydroxide  is  slightly  soluble, 
less  than  calcium  sulphate,  but  sufficiently  soluble  to  be  employed  as 
a  reagent.  Hydroxides  of  the  other  metals  are  either  insoluble  or  so 
little  soluble  as  to  be  classed  insoluble.  These  are  obtained  as  pre- 
cipitates by  adding  a  soluble  hydroxide  (usually  of  sodium,  potas- 
sium, or  ammonium)  to  a  salt  of  the  metals  whose  hydroxides  are  in- 
soluble. The  principle  involved  here  is  the  same  as  in  the  case  of 
precipitation  of  insoluble  carbonates,  namely,  bringing  together  in 
solution  constituents  which  by  their  union  can  form  insoluble  prod- 
ucts and  thus  be  eliminated  from  the  solution,  thereby  allowing  the 
reaction  to  go  on  to  completion.  This  reaction  is  given  as  a  test  under 
many  of  the  metals. 

Ammonium  hydroxide  acts,  in  general,  like  the  alkalies,  but 
toward  certain  metals  it  shows  a  marked  difference.  For  example, 
calcium  hydroxide  is  precipitated  from  fairly  concentrated  solutions 
of  calcium  salts  by  the  alkalies,  but  not  by  ammonia  water.  This  is 
explained  by  the  ionic  or  dissociation  theory  by  the  fact  that  ammo- 
nium hydroxide  is  only  slightly  dissociated.  According  to  this 
theory,  practically  all  reactions  in  aqueous  solutions  take  place  be- 
tween ions  (see  page  195).  The  alkalies  are  largely  dissociated  into 
metal  ions  and  (OH)  ions,  which  latter  unite  with  the  metal  ions  of 
the  other  metals  to  form  the  slightly  ionized  and  insoluble  hydrox- 
ides. Now  ammonium  hydroxide  is  only  slightly  ionized — in  fact, 
to  a  less  extent  than  calcium  hydroxide — so  that  only  a  small  amount 
of  calcium  hydroxide  is  formed,  which  remains  in  solution,  because 
somewhat  soluble.  The  presence  of  this  calcium  hydroxide  in  solu- 
tion prevents  further  ionization  of  the  ammonium  hydroxide  to  such 
an  extent  that  it  ceases  to  act  as  an  alkali  or  soluble  hydroxide.  In 
fact,  the  slight  ionization  of  ammonium  hydroxide  accounts  for  the 
reverse  action,  namely,  the  liberation  of  ammonia  from  its  salts  by 
the  action  of  calcium  hydroxide. 

In  the  presence  of  ammonium  salts,  ammonium  hydroxide  ionizes 
only  to  a  very  slight  extent,  so  that  it  loses  almost  all  the  character 
of  a  hydroxide  as  far  as  precipitating  other  metallic  hydroxides  is 
concerned,  only  the  extremely  insoluble  ones  being  precipitated. 
This  accounts  for  the  fact  that  magnesium  hydroxide  is  not  precipi- 
tated by  ammonia  water  when  ammonium  salts  are  present.  The 
magnesium  hydroxide,  although  being  nearly  insoluble,  is  sufficiently 
soluble  and  ionizable  not  to  be  precipitated  by  ammonia  water  under 
these  conditions.  Alkalies,  on  the  other  hand,  precipitate  magnesium 
hydroxide  copiously,  because  they  are  almost  completely  ionized  in 


276  METALS  AND   THEIR  COMBINATIONS. 

dilute  solutions,  and  thus  act  as  strong  bases,  as  we  say.  Ammonium 
carbonate  behaves  very  much  like  ammonia  water  toward  magnesium 
and  some  other  metals. 

Hydroxides  of  nearly  all  metals,  when  heated  sufficiently,  lose 
water  and  give  the  oxide.  Many  oxides  are  prepared  in  this  way. 
Only  a  few  oxides  unite  with  water  to  form  a  hydroxide.  One  of  the 
best  examples  of  this  is  the  process  of  slaking  lime.  Oxides  may 
also  be  obtained  by  heating  carbonates  or  nitrates,  or  directly  from 
the  metals.  The  method  followed  in  any  particular  case  is  deter- 
mined by  the  properties  of  the  metal,  the  question  of  economy,  etc. 

Tests  for  magnesium. 
(Use  the  reagent  solution  of  magnesium  sulphate.  ) 

1.  The  addition  of  an  alkali  carbonate  solution  causes  a  white  pre- 
cipitate of  basic  magnesium  carbonate  (see  Experiment  25). 

2.  Add  to  the  solution  some  caustic  alkali :  a  white  precipitate  of 
magnesium  hydroxide,  Mg(OH)2,  is  formed,  insoluble  in  excess  of  alkali. 

Mg"  +  SO/'  +  2Na'  +  2(OH)'  =  Mg(OH),  +  2Na'  +  SO/'. 

3.  Add  to  the  solution  ammonia  water  or  ammonium  carbonate : 
part  of  the  magnesium  is  precipitated  as  hydroxide  or  carbonate. 
The  latter  is  increased  on  heating.     If  an  equal  volume  of  ammo- 
nium chloride  solution  is  previously  added,  no  precipitate  is  obtained 
(for  explanation,  see  Remarks  on  Tests  above). 

4.  To  the  solution  add  an  equal  volume  of  solution  of  ammonium 
chloride  and  some  ammonia  water.     The  mixture  should  be  clear. 
Then  add  sodium  phosphate  solution  :  a  white,  finely  crystalline  pre- 
cipitate of  the  double  salt,  ammonium  magnesium  phosphate,  is  pro- 
duced, which  increases  by  shaking  (see  reactions  under  test  1  for 
phosphoric  acid).     This  is  a  delicate  and  decisive  test  for  magnesium, 
when  other  metals  which  resemble  it  are  eliminated.     This  is  easily 
done  by  adding  to  a  solution  some  chloride,  sulphide,  and  carbonate 
of  ammonium,  which  will  remove  by  precipitation  all  metals  except 
magnesium  and  alkali  metals. 

QUESTIONS. — How  is  magnesium  found  in  nature?  By  what  process  is 
metallic  magnesium  obtained?  Give  the  physical  and  chemical  properties  of 
magnesium.  State  two  methods  by  which  magnesium  oxide  can  be  obtained. 
What  is  calcined  magnesia?  State  the  composition  and  properties  of  the 
official  magnesium  carbonate,  and  how  it  is  made.  What  is  Epsom  salt,  and 
how  is  it  obtained?  Which  compounds  of  magnesium  are  insoluble?  Give 
tests  for  magnesium  compounds.  How  can  the  presence  of  magnesium  be 
demonstrated  in  a  mixture  of  magnesium  sulphate  and  sodium  sulphate  ? 


CALCIUM.  277 

25.    CALCIUM.     STRONTIUM.    BARIUM. 
Ca"  =  40  (39.81 ).       Sr"  =  86.94.       Ba"  =  136.4. 

General  remarks  regarding  the  metals  of  the  alkaline  earths. 

The  three  metals,  calcium,  barium,  and  strontium,  form  the  second 
group  of  light  metals.  Similar  to  the  alkali-metals,  they  decompose 
water  at  the  ordinary  temperature  with  liberation  of  hydrogen;  their 
separation  in  the  elementary  state  is  even  more  difficult  than  that  of 
the  alkali-metals. 

They  differ  from  the  latter  by  forming  insoluble  carbonates  and 
phosphates  (those  of  the  alkalies  are  soluble),  from  the  earths  by 
their  soluble  hydroxides  (those  of  the  earths  are  insoluble),  and  from 
all  heavy  metals  by  the  solubility  of  their  sulphides  (those  of  heavy 
metals  are  insoluble). '  The  sulphates  are  either  insoluble  (barium) 
or  sparingly  soluble  (strontium  and  calcium).  The  hydroxides  and 
carbonates  are  decomposed  by  heat,  water  or  carbon  dioxide  being 
expelled  and  the  oxides  formed.  In  case  of  calcium  carbonate  this 
decomposition  takes  place  easily,  while  the  carbonates  of  barium 
and  strontium  require  a  much  higher  temperature.  They  are  bivalent 
elements. 

Occurrence  in  nature.  Calcium  is  one  of  the  most  abundantly 
occurring  elements.  As  carbonate  (CaCO3)  it  is  found  in  the  form 
of  calc-spar,  limestone,  chalk,  marble,  shells  of  eggs  and  mollusca, 
etc.,  or,  as  acid  carbonate,  dissolved  in  water.  The  sulphate  is  found 
as  gypsum  or  alabaster,  CaSO42H2O;  the  phosphate,  Ca3(PO4)2,  in 
the  different  phosphatic  rocks  (apatite,  etc.) ;  the  fluoride,  CaF2,  as 
fluor-spar;  the  chloride,  CaCl2,  in  some  waters,  and  the  silicate  in 
many  rocks.  It  enters  the  vegetable  and  animal  system  in  various 
forms  of  combination,  chiefly,  however,  as  phosphate  and  sulphate. 

Calcium  oxide,  Lime,  Calx,  CaO  =  55.68  (Quick-lime,  Burned 
lime),  is  obtained  on  a  large  scale  by  the  common  process  of  lime- 
burning,  which  is  the  heating  of  limestone  or  any  other  calcium  car- 
bonate to  about  800°  C.  (1472°  F.),  in  furnaces  termed  lime-kilns. 
On  a  small  scale  decomposition  may  be  accomplished  in  a  suitable 
crucible  over  a  blowpipe  flame : 

CaCO3  =  CaO  +  CO2. 

The  pieces  of  oxide  thus  formed  retain  the  shape  and  size  of  the 
carbonate  used  for  decomposition. 

Lime  is  a  white,  odorless,  amorphous,  infusible  substance,  of  alka- 


278  METALS  AND  THEIR  COMBINATIONS. 

line  taste  and  reaction;  exposed  to  the  air  it  gradually  absorbs 
acid  among  acids,  and  is  used  directly  or  indirectly  in  many  branches 
of  chemical  manufacture. 

Calcium  hydroxide,  Calcium  hydrate,  Ca(OH)2  (Slaked  lime). 
When  water  is  sprinkled  upon  pieces  of  calcium  oxide,  the  two  sub- 
stances combine  chemically,  liberating  much  heat;  the  pieces  swell 
up,  and  are  converted  gradually  into  a  dry,  white  powder,  which  is 
the  slaked  lime.  When  this  is  mixed  with  water,  the  so-called  milk 
of  lime  is  formed. 

Freshly  slacked  lime,  made  into  a  thin  paste  with  water  and  mixed  with  3 
to  4  times  as  much  sand  as  lime  used,  forms  the  ordinary  mortar,  employed  for 
building  purposes.  The  hardening  of  mortar  is  due  first  to  loss  of  water,  fol- 
lowed by  a  gradual  conversion  of  calcium  hydroxide  into  carbonate.  In  the 
course  of  years  calcium  silicate  is  also  formed. 

Lime-water,  Liquor  calcis  (Solution  of  lime).  This  is  a  sat- 
urated solution  of  calcium  hydroxide  in  water :  10,000  parts  of  the 
latter  dissolving  about  15  to  17  parts  of  hydroxide.  In  making 
lime-water,  1  part  of  calcium  oxide  is  slaked  and  agitated  occasionally 
during  half  an  hour  with  30  parts  of  water.  The  mixture  is  then 
allowed  to  settle,  and  the  liquid,  containing  besides  calcium  hydroxide 
the  salts  of  the  alkali-metals  which  may  have  been  present  in  the 
lime,  is  decanted  and  thrown  away.  To  the  calcium  hydroxide  left, 
and  thus  purified,  300  parts  of  water  are  added  and  occasionally 
shaken  in  a  well -stoppered  bottle,  from  which  the  clear  liquid  may 
be  poured  off  for  use. 

Lime-water  is  a  colorless,  odorless  liquid,  having  a  feebly  caustic 
taste  and  an  alkaline  reaction.  When  heated  to  boiling  it  becomes 
turbid  by  precipitation  of  calcium  hydroxide  (or  perhaps  oxide)  which 
re-dissolves  when  the  liquid  is  cooled.  Carbon  dioxide  causes  a  pre- 
cipitation of  calcium  carbonate,  soluble  in  an  excess  of  carbonic  acid. 

Experiment  27.    Make  lime-water  according  to  directions  given  above. 

Calcium  carbonate,  Calcii  carbonas  praecipitatus,  CaCO3  = 
99.35.  Precipitated  calcium  carbonate  is  obtained  as  a  white,  taste- 
less, neutral,  impalpable  powder  by  mixing  solutions  of  calcium 
chloride  and  sodium  carbonate: 

CaCl2  +  Na^CO,  =  2NaCl  +  CaCO3. 


CALCIUM.  279 

Experiment  28.  Add  to  about  10  grammes  of  marble  (calcium  carbonate),  in 
small  pieces,  hydrochloric  acid  as  long  as  effervescence  takes  place ;  filter  the 
solution  of  calcium  chloride  thus  obtained  and  add  to  it  solution  of  sodium 
carbonate  as  long  as  a  precipitate  is  formed,  collect  the  precipitate  on  a  filter, 
wash  and  dry  it. 

Dried  calcium  sulphate,  Calcii  sulphas  exsiccatus,  CaSO4  =; 
135.15  (Dried  gypsum,  Plaster-of-Paris,  Calcined  plaster).  It  has 
been  mentioned  above  that  the  mineral  gypsum  is  native  calcium 
sulphate  in  combination  with  2  molecules  of  water  of  crystallization, 
By  heating  to  about  115°  C.  (239°  F.)  about  three-fourths  of  this 
water  is  expelled,  and  a  nearly  anhydrous  sulphate  formed.  This 
article  readily  recombines  with  water,  becoming  a  hard  mass,  for 
which  reason  it  is  used  for  making  moulds  and  casts,  and  in  surgery. 
If  the  gypsum  is  heated  to  a  higher  temperature  than  the  one  men- 
tioned, all  water  is  expelled,  and  the  product  thus  obtained  combines 
with  water  but  very  slowly. 

Precipitated  calcium  phosphate,  Calcii  phosphas  preecipitatus, 
Cas(p04)2  =  307.98  (Phosphate  of  lime).  By  dissolving  bone-ash 
(bone  from  which  all  organic  matter  has  been  expelled  hy  heat)  in 
hydrochloric  acid,  and  precipitating  the  solution  with  ammonia  water 
there  is  obtained  calcium  phosphate,  which  contains  traces  of  calcium 
fluoride  and  magnesium  phosphate. 

A  pure  article  is  made  by  precipitating  a  solution  of  calcium 
chloride  by  sodium  phosphate  and  ammonia : 

2Na2HPO4  +  3CaCl2  +  2NH4OH  =  Ca3(PO4)2  +  4NaCl  +  2NH4C1  +  2H2O. 

It  is  a  white,  tasteless,  amorphous  powder,  insoluble  in  cold  water, 
soluble  in  hydrochloric  or  nitric  acids. 

Superphosphate,  or  acid  phosphate  of  lime.  Among  the  inorganic  sub- 
stances which  serve  as  plant-food,  calcium  phosphate  is  a  highly  important 
one.  As  this  compound  is  found  usually  in  very  small  quantities  as  a  con- 
stituent of  the  soil,  and  as  this  small  quantity  is  soon  removed  by  the  various 
crops  taken  from  a  cultivated  soil,  it  becomes  necessary  to  replace  it  in  order 
to  enable  the  plant  to  grow  and  to  form  seeds. 

For  this  purpose  the  various  phosphatic  rocks  (chiefly  calcium  phosphate) 
are  converted  into  commercial  fertilizers,  which  is  accomplished  by  the  addi- 
tion of  sulphuric  acid  to  the  ground  rock.  The  sulphuric  acid  removes  from 
the  tricalcium  phosphate  one  or  two  atoms  of  calcium,  forming  mono-  or 
dicalcium  phosphate  and  calcium  sulphate.  The  mixture  of  these  substances, 
containing  also  the  impurities  originally  present  in  the  phosphatic  rocks,  is 
sold  as  acid  phosphate  or  superphosphate. 

Bone-black  and  bone-ash.  Phosphates  enter  the  animal  system 
in  the  various  kinds  of  food,  and  are  to  be  found  in  every  tissue  and 


280  METALS  AND   THEIR   COMBINATIONS. 

fluid,  but  most  abundantly  in  the  bones  and  teeth.  Bones  contain 
about  30  per  cent,  of  organic  and  70  per  cent,  of  inorganic  matter, 
most  of  which  is  tricalcium  phosphate.  When  bones  are  burned  until 
all  the  organic  matter  has  been  destroyed  and  volatilized,  the  result- 
ing product  is  known  as  bone-ash.  If,  however,  the  bones  are  sub- 
jected to  the  process  of  destructive  distillation  (heating  with  exclusion 
of  air),  the  organic  matter  suffers  decomposition,  many  volatile 
products  escape,  and  most  of  the  non-volatile  carbon  remains  mixed 
with  the  inorganic  portion  of  the  bones,  which  substance  is  known 
as  bone-black  or  animal  charcoal,  carbo  animalis.  It  contains  about 
85  per  cent,  of  inorganic  matter,  the  balance  being  chiefly  carbon. 

Calcium  hypophosphite,  Calcii  hypophosphis,  Ca(PH2O2)2  = 
168.86.  Obtained  by  heating  pieces  of  phosphorus  with  milk  of  lime 
until  hydrogen  phosphide  ceases  to  escape.  From  the  filtered  liquid 
the  excess  of  lime  is  removed  by  carbon  dioxide,  and  the  clear  liquid 
evaporated  to  dryness.  (Great  care  must  be  taken  during  the  whole 
of  the  operation,  which  is  somewhat  dangerous  on  account  of  the 
inflammable  and  explosive  nature  of  the  compounds.) 

8P  +  6H2O  +  3[Ca(OH)2]  =  3[Ca(PH2O2)2]  +  2PH3. 

Calcium  hypophosphite  is  generally  met  with  as  a  white,  crystal- 
line powder  with  a  pearly  lustre ;  it  is  soluble  in  6  parts  of  water 
and  has  a  neutral  reaction  to  litmus. 

Calcium  chloride,  Calcii  chloridum,  CaCl2  =  11O.16,  and 
Calcium  bromide,  Calcii  bromidum,  CaBr2  =  198.52,  may  both 
be  obtained  by  dissolving  calcium  carbonate  in  hydrochloric  acid  or 
hydrobromic  acid,  until  the  acids  are  neutralized.  Both  salts  are 
highly  deliquescent. 

Chlorinated  lime,  Calx  chlorinata  (Bleaching -powder,  incorrectly 
called  Chloride  of  lime\  This  is  chiefly  a  mixture  (according  to  some, 
a  compound)  of  calcium  chloride  with  calcium  hypochlorite,  and  is 
manufactured  on  a  very  large  scale  by  the  action  of  chlorine  upon 
calcium  hydroxide : 

2Ca(OH)2    +    4C1  =  2H20  +  Ca(ClO)2  +  CaCl2. 
Calcium  hydroxide.  Chlorinated  lime. 

Bleaching-powder  is  a  white  powder,  having  a  feeble  chlorine-like 
odor ;  exposed  to  the  air  it  becomes  damp  from  absorption  of  moist- 
ure, undergoing  decomposition  at  the  same  time;  with  dilute  acids  it 


CALCIUM.  281 

evolves  chlorine,  of  which  it  should  contain  not  less  than  30  per  cent, 
in  available  form.     The  action  of  hydrochloric  acid  takes  place  thus: 

Ca(ClO),  -f  2HC1  =  CaCl2  +  2HC1O; 
2HC10  -f  2HC1  =  2H2O  +  4C1. 

Bleaching-powder  is  a  powerful  disinfecting  and  bleaching  agent. 

Sulphurated  lime,  Calx  sulphurata,  is  a  mixture  of  calcium  sulphide  and 
sulphate,  obtained  by  heating  to  redness  in  a  crucible  a  mixture  of  dried  cal- 
cium sulphate,  starch,  and  charcoal  until  the  contents  have  lost  their  black 
color.  By  the  deoxidizing  action  of  the  coal  and  starch  the  larger  portion  of 
the  calcium  sulphate  is  converted  into  sulphide. 

Calcium  carbide,  C.2Ca,  is  manufactured  on  a  large  scale  by  heating  in 
an  electric  furnace  a  mixture  of  lime  and  coal,  or  coal-tar.  The  combined 
action  of  the  high  temperature  and  of  the  electric  current  causes  this  decompo* 
sition  to  take  place  : 

CaO  +  30  =  CaC2  +  CO. 

Calcium  carbide  thus  made  is  not  pure;  it  forms  gray  or  brown  masses  of 
extreme  hardness ;  it  is  used  extensively  for  generating  acetylene  gas,  C2H8,  which 
is  evolved  when  calcium  carbide  acts  on  water : 

C2Ca  +  H2O  =  C2H2  -f-  CaO. 

Tests  for  calcium. 
(The  reagent  solution  of  calcium  chloride,  CaCl^  may  be  used.) 

1.  Add  to  solution  of  a  calcium  salt,  the  carbonate  of  either  potas- 
sium, sodium,  or  ammonium  :  a  white  precipitate  of  calcium  carbon- 
ate, CaCO3,  is  produced.     Try  the  test  also  on  solution  of  calcium 
sulphate  and  lime-water. 

2.  Add  sodium  phosphate  to  neutral  solution  of  a  calcium  salt :  a 
white  precipitate  of  calcium  phosphate,  CaHPO4,  is  produced. 

3.  Add  ammonium  (or  potassium)  oxalate  to  solution  of  a  calcium 
salt :  a  white  precipitate    of  calcium  oxalate,  CaC2O4,  is    produced, 
which  is  insoluble  in  acetic,  soluble  in  hydrochloric  acid.     Try  the  test 
also  on  solution  of  calcium  sulphate  and  lime-water. 

4.  Sulphuric  acid  or  soluble  sulphates  produce  a  white  precipitate 
of  calcium  sulphate,  CaSO4,  in  concentrated,  but  not  in  dilute  solu- 
tions of  a  calcium  salt.    Try  the  test  also  on  lime-water. 

5.  Add  potassium  or  sodium  hydroxide  :    a  white  precipitate  of 
calcium  hydroxide,  Ca(OH)2,  is  produced  in  concentrated,  but  not  in 
diluted  solutions.    Ammonia  water  gives  no  precipitate.  (See  Remarks 
on  Tests,  page  274.) 

6.  Volatile  compounds  of  calcium  impart  a  reddish-yellow  color  to 
the  Bunsen  flame.    Non-volatile  compounds,  as  the  oxide,  carbonate, 
phosphate,  etc.,  have  scarcely  any  effect  on  the  flame.    (Try  it.)   These 


282  METALS  AND   THEIR   COMBINATIONS. 

should  first  be  moistened  with  strong  hydrochloric  acid  to  convert 
them  to  the  volatile  chloride  before  introducing  into  the  flame.  (See 
note  to  test  4  for  potassium.) 

Test  3,  done  in  dilute  solution,  combined  with  tests  4  and  6,  is 
decisive  for  recognizing  calcium  compounds.  The  oxide,  carbonate, 
and  phosphate  may  be  dissolved  by  dilute  hydrochloric  acid  for  tests. 
The  phosphate  solution  cannot  be  neutralized  without  precipitation, 
but  if  left  weakly  acid  and  considerably  diluted  test  3  can  be  applied. 

The  above  tests  are  examples  of  more  or  less  complete  reactions,  due  to  the 
formation  of  insoluble  or  sparingly  soluble  substances,  and  their  removal  from 
the  field  of  action  by  precipitation  (see  pages  116  and  193).  The  ionic  equa- 
tions in  the  tests  are  as  follows : 

Test  1.    Ca"  -f  2C1'        +  2Na'  +  CO3"     =  CaCO3  +  2Na"  +  2C1'; 
Ca"  +  SO/'      +  2Na'  +  CO3"       =  CaCO3  +  2Na'  +  SO/'; 
Ca"  +  2(OH)'  +  2Na-  +  CO3"       -  CaCO3  +  2Na'  +  2(OH)'. 

Test  2.     Ca"  +  2C1'        +  2Na'  +  HPO4"  =  CaHPO4  +  2Na-  +  2C1'; 
Test  3.    Ca"  +  2C1'       +  2NH4'+  C,O4"      =  CaC2O4      +  2NH4-  -f-  2C1'. 
The  equations  for  sulphate  and  hydroxide  of  calcium  are  similar  (see  test  1). 
Test  4.    Ca"  +  2C1'       +  2H-    +  SO/'       =  CaSO4       +  2H-  4-  2C1'; 
Test  5.     Ca"  +  2C1'       +  2Na«  +  2(OH)7  =  Ca(OH)2  +  2Na«  -f-  2C1'. 

The  ionic  equations  in  the  tests  for  strontium  and  barium  are  like  those  for 
calcium. 

Strontium,  Sr"  =  86.94.  Found  in  a  few  localities  in  the  minerals 
strontianite,  SrCO3,  and  celestite,  SrSO4.  Its  compounds  resemble 
those  of  calcium  and  barium.  The  oxide,  SrO,  cannot  be  obtained 
easily  by  heating  the  carbonate,  as  this  is  much  more  stable  than 
calcium  carbonate.  It  may,  however,  be  readily  prepared  by  heating 
the  nitrate.  The  hydroxide,  Sr(OH)2,  is  formed  when  the  oxide  is 
brought  in  contact  with  water;  it  is  more  soluble  than  calcium 
hydroxide. 

Strontium  nitrate,  Sr(NO3)2,  Strontium  chloride,  SrCl2,  Strontium 
bromide,  SrBr2,  and  Strontium  iodide,  SrI2,  may  be  obtained  by  dis- 
solving the  carbonate  in  the  respective  acids.  The  nitrate  is  used 
extensively  for  pyrotechnic  purposes,  as  strontium  imparts  a  beau- 
tiful red  color  to  flames ;  the  bromide  and  iodide  are  official. 

Tests  for  strontium. 

(Use  about  a  5  per  cent,  solution  of  strontium  nitrate.) 

1 .  The  reactions  of  strontium  with  soluble  carbonates,  oxalates,  and 
phosphates  are  analogous  to  those  of  calcium. 


STRONTIUM.  283 

2.  Add  calcium  sulphate  solution  :  a  white  precipitate  of  strontium 
sulphate,  SrSO4,  is  formed  after  a  few  minutes.     This  test  shows  that 
the  sulphate  is  less  soluble  than  calcium  sulphate. 

3.  Add  dilute  sulphuric   acid  or  a  solution  of  a  sulphate  :  a  white 
precipitate   forms  at  once   in    concentrated,  after   a  while  in  dilute, 
solutions. 

4.  Add  potassium  chromate  solution  :  a  pale-yellow  precipitate  of 
strontium  chromate,  SrCrO4,  is  formed,  which  is  soluble  in  acetic  acid 
and  in  hydrochloric  acid.      (Potassium  dichromate  causes  no  precipi- 
tation.) 

5.  Volatile  strontium  compounds  color  the  Bunsen  flame  crimson 
(see  remarks  in  test  6  for  calcium.)     The  color  appears  at  the  moment 
when  the  substance  is  first  introduced  into  the  flame,  whereby  the  color 
can  be  seen,  even  in  the  presence  of  barium.     Lithium  is  the  only 
other  metal  which  gives  a  similar  flame,  but  strontium  may  be  dis- 
tinguished from  it  by  test  3  applied  in  somewhat  dilute  solution. 

Tests  2  and  3  combined  with  5  give  conclusive  proof  of  strontium 
compounds.  Insoluble  compounds  are  treated  as  directed  under  tests 
for  calcium. 

Barium,  Ba11  =  136.4.  Occurs  in  nature  chiefly  as  sulphate  in 
barite  or  heavy  spar,  BaSO4,  but  also  as  carbonate  in  witherite,  BaCO3. 
Barium  and  its  compounds  resemble  closely  those  of  calcium  and 
strontium. 

Barium  chloride,  BaCl2  +  2H2O,  is  prepared  by  dissolving  the 
carbonate  in  hydrochloric  acid.  It  crystallizes  in  prismatic  plates, 
and  is  used  as  a  valuable  reagent. 

Barium  dioxide  or  peroxide,  BaO2,  is  made  by  heating  the  oxide  to 
a  dark -red  heat  in  the  air  or  in  oxygen.  When  heated  above  the  tem- 
perature at  which  it  is  formed,  decomposition  into  oxide  and  oxygen 
takes  place.  This  power  to  absorb  oxygen  from  air  and  to  give  it  up 
again  at  a  higher  temperature  has  been  used  as  a  method  of  preparing 
oxygen  on  the  large  scale.  Unfortunately,  the  barium  oxide  cannot 
be  used  for  an  unlimited  number  of  operations,  as  it  loses  the  power 
to  absorb  oxygen  after  it  has  been  heated  several  times.  The  use 
made  of  barium  dioxide  in  preparing  hydrogen  dioxide  has  been 
mentioned  before. 

Barium  dioxide  is  a  heavy,  grayish-white,  amorphous  powder, 
almost  insoluble  in  water,  with  which,  however,  it  forms  a  hydroxide, 
and  to  which  it  imparts  an  alkaline  reaction. 


284  METALS  AND  THEIR  COMBINATIONS. 

Barium  oxide,  BaO,  is  made  by  heating  barium  nitrate,  Ba(N03)2,  which 
itself  is  made  by  dissolving  barium  carbonate  in  nitric  acid. 

Barium  salts  are  poisonous  ;  antidotes  are  sodium  and  magnesium  sulphates. 

Tests  for  barium. 
(Use  the  reagent  solution  of  barium  chloride.) 

1.  The  reactions  of  barium  salts  with  soluble  carbonates,  oxalates, 
and  phosphates  are  analogous  to  those  of  solutions  of  calcium  salts. 

2.  Add  dilute  sulphuric  acid  or  solution  of  a  sulphate  :  a  white 
precipitate  of  barium  sulphate,  BaSO4,  is  produced  immediately,  even 
in  dilute  solutions.     The  precipitate  is  insoluble  in  all  diluted  acids. 

3.  Add  calcium  sulphate  solution  :  a  white  precipitate,  insoluble  in 
all  diluted  acids,  is  formed  immediately  (compare  with  test  2  under 
Strontium). 

4.  Add  potassium  chromate  or  dichromate  solution  :  a  pale-yellow 
precipitate  of  barium  chromate,  BaCrO4,  is  formed,  insoluble  in  acetic 
acid,  but  soluble  in  hydrochloric  or  nitric  acid. 

5.  Volatile  barium  compounds   color   a  Buusen  flame  yellowish 
green  (see  remarks  under  test  6  for  calcium). 

Tests  3, 4,  and  5  give  conclusive  proof  of  barium.  Insoluble  com- 
pounds are  treated  as  directed  under  tests  for  calcium. 

Radium,  Ha  =  223.3,  This  element,  discovered  in  1899,  has  been  men- 
tioned in  the  article  on  radio-activity,  page  85.  While  radium  is  closely 
related  to  barium  it  has  not  been  found  in  the  native  barium  compounds,  except 
when  they  occur  associated  with  uranium  as  in  pitch-blende,  an  ore  from  which 
uranium  compounds  are  extracted.  This  ore  contains,  however,  but  0.1  gramme 
of  radium  in  1000  kilograms,  which  is  equal  to  0.00001  per  cent.  The  residue 
left,  after  the  uranium  has  been  eliminated,  contains  from  2  to  3  times  as  much 
radium  as  the  original  ore.  From  1000  kilograms  of  this  residue  10  to  15  kilo- 
grams of  radiferous  barium  salt  (chloride  or  bromide)  are  extracted,  and  from 

QUESTIONS. — Which  metals  form  the  group  of  the  alkaline  earths,  and  in 
what  respect  do  their  compounds  differ  from  those  of  the  alkali-metals?  How 
is  calcium  found  in  nature?  What  is  burned  lime;  from  what,  and  by  what 
process  is  it  made,  and  how  does  water  act  on  it?  What  is  lime-water;  how 
is  it  made,  and  what  are  its  properties?  Mention  some  varieties  of  calcium 
carbonate  as  found  in  nature,  and  how  is  it  obtained  by  an  artificial  process 
from  the  chloride  ?  What  is  Plaster-of-Paris,  and  what  is  gypsum ;  what  are 
they  used  for?  State  composition  and  mode  of  manufacturing  bleaching- 
powder ;  what  are  its  properties,  and  how  do  acids  act  upon  it  ?  What  is  bone- 
black,  bone-ash,  acid  phosphate,  and  precipitated  tricalcium  phosphate  ?  How 
are  they  made?  Give  tests  for  barium,  calcium,  and  strontium  ;  how  can  they 
be  distinguished  from  each  other  ?  Which  compounds  of  barium  and  stron- 
tium are  of  interest,  and  what  are  they  used  for? 


ALUMINUM. 


285 


this  the  radium  salt  is  prepared  by  repeated  fractional  crystallization.  The 
small  yield  of  radium  obtained  after  long  and  tedious  operations  make  it  the 
most  costly  material  of  the  day. 

Both  the  chloride  and  bromide  of  radium  are  white,  crystalline  substances 
turning  grayish  in  the  course  of  time.  Lack  of  a  liberal  supply  of  radium  has 
so  far  prevented  a  closer  study  of  its  chemical  behavior. 

Summary  of  analytical  characters  of  the  alkaline  earth-metals. 


Magnesium. 

Calcium. 

Strontium. 

Barium. 

Yellow  pre- 

Yellow pre- 

cipitate. 
Yellow  pre- 

cipitate. 
White  pre- 

cipitate. 
White  pre- 

Ammonium carbonate  .     . 

White  preci- 
pitate soluble 
in  NH4C1. 
\Vhite  pre- 

White pre- 
cipitate. 

cipitate  form- 
ing slowly 
White  pre- 
cipitate. 

cipitate  form- 
ing at  once. 
White  pre- 
cipitate. 

Ammonium  oxalate  .     .     . 
Sodium  phosphate    .     .     . 

cipitate 
No  precipi 
tate  unless 
very  con- 
centrated 
White  pre- 
cipitate. 

White  pre- 
cipitate in 
dilute 
solution 
White  pre- 
cipitate. 
Yello  wish- 

White  pre- 
cipitate in 
strong 
solution. 
White  pre- 
cipitate. 
Eed 

White  pre- 
cipitate in 
strong 
solution. 
White  pre- 
cipitate 
Yellowish- 

One  part  of   hydroxide  is 
soluble  in   

One    part    of   sulphate    is 
soluble  in    

50,000  parts 
of  water. 

1.5  parts  of 

red. 

666  parts  of 
water. 

400  parts  of 

50    parts    of 
water. 

8000  parts  of 

green. 

28.6  parts  of 
water. 

400,000  parts 

water. 

water. 

water. 

of  water. 

26.  ALUMINUM. 

Aliu  27  (26.9). 

Aluminum  is  the  representative  of  the  metals  of  the  earths  proper ; 
all  other  members  of  this  class  are  found  in  nature  in  very  small 
quantities,  and  are  chiefly  of  scientific  interest,  with  the  exception  of 
cerium,  which  furnishes  an  official  preparation. 

Occurrence  in  nature.  Aluminum  is  found  almost  exclusively 
in  the  solid  mineral  portion  of  the  earth ;  rarely  more  than  traces  of 
aluminum  compounds  are  found  dissolved  in  water,  and  the  occur- 
rence of  aluminum  in  the  animal  organism  seems  to  be  purely 
accidental. 

By  far  the  largest  quantity  of  aluminum  is  found  in  combination 


286  METALS  AND   THEIR   COMBINATIONS. 

with  silicic  acid  in  the  various  silicated  rocks  forming  the  greater 
mass  of  our  earth,  such  as  feldspar,  slate,  basalt,  granite,  mica,  horn- 
blende, etc.,  or  in  the  various  modifications  of  clay  formed  by  their 
decomposition. 

The  minerals  known  as  corundum,  ruby,  sapphire,  and  emery,  are 
aluminum  oxide  in  a  crystallized  state,  and  more  or  less  colored  by 
traces  of  other  substances. 

Metallic  aluminum  may  be  obtained  by  the  decomposition  of 
aluminum  chloride  by  metallic  sodium  : 

A1C13  +  3Na  —  SNaCl  -f  Al. 

It  is  now  manufactured  by  the  electrolysis  of  aluminum  and  sodium 
fluoride,  or  of  other  aluminum  compounds. 

Aluminum  is  an  almost  silver- white  metal  of  a  very  low  specific 
gravity  (2.67) ;  it  is  capable  of  assuming  a  high  polish,  and  for  this 
reason  is  used  for  ornamental  articles ;  it  is  very  ductile  and  malleable 
and  ranks  with  silver  in  hardness,  as  also  in  its  power  of  conducting 
heat  and  electricity. 

Aluminum  is  not  oxidized  to  any  great  extent  in  dry  or  moist  air 
nor  is  it  affected  by  hydrogen  sulphide.  It  is  not  readily  acted  on  by 
nitric  or  sulphuric  acid,  but  easily  dissolves  in  hydrochloric  acid  and 
in  solutions  of  the  alkali  hydroxides. 

Aluminum  forms  alloys  with  nearly  all  metals,  lead  being  an  exception. 
The  hardness  and  elasticity  of  tin  is  increased  by  addition  of  aluminum  ; 
readily  obtainable  alloys  with  zinc  are  used  as  solders  for  aluminum.  A  small 
quantity  of  aluminum  added  to  wrought  iron  so  increases  its  fusibility  that  it 
may  be  poured  as  easily  as  cast  iron.  Largely  used  is  aluminum-bronze,  an  alloy 
resembling  gold  and  composed  of  10  parts  of  aluminum  with  90  of  copper. 

Aluminum  would  be  an  ideal  base  for  artificial  dentures,  were  it  not  that 
the  corrosive  action  of  alkaline  fluids  upon  it  limits  its  use. 

Aluminum  is  trivalent,  and  the  composition  of  the  chloride  and 
hydroxide  is  therefore  given  as  A1C13  and  Al(OH),  respectively. 

Alum  is  the  general  name  for  a  group  of  isomorphous  double  sul- 
phates containing  an  atom  each  of  a  univaletit  and  a  trivalent  metal, 
combined  in  crystallizing  with  12  molecules  of  water.  The  general 
formula  of  an  alum  is  consequently  MiMiii(SO4)2.12H2O.  Mi  repre- 
sents in  this  case  a  univalent,  Miu  a  trivalent  metal. 

Alums  known  are,  for  instance  : 

Ammonium-aluminum  sulphate,    NH4A1(SO4)2.12H2O. 
Potassium-chromium  sulphate,       KCr(SO4)2.12H2O. 
Ammonium-ferric  sulphate,  NH4Fe(SO4)8.12H8O. 


ALUMINUM.  287 

The  official  alum,  (i/iimen,  is  the  potassium  alum,  KA1(SO4)2.12H2O 
=  471.02,  a  white  salt  crystallizing  in  large  octahedrons,  soluble  in 
10  parts  of  cold  and  0.3  part  of  boiling  water;  this  solution  has  an 
acid  reaction  and  a  sweetish  astringent  taste. 

Alum  is  manufactured  on  a  large  scale  by  decomposing  certain 
kinds  of  clay  (aluminum  silicates)  by  sulphuric  acid,  when  aluminum 
sulphate  is  formed,  to  the  solution  of  which  potassium  or  ammonium 
sulphate  is  added,  when,  on  evaporation,  potassium  or  ammonium 
alum  crystallizes. 

Dried  alum;  Alumen  exsiccatum,  KA1(SO4)2  =  256.46  (Burnt 
alum).  This  is  common  alum,  from  which  the  water  of  crystallization 
has  been  expelled  by  heat.  It  is  a  white  powder,  dissolving  very 
slowly  in  cold,  but  quickly  in  boiling  water. 

Aluminum  hydroxide,  Alumini  hydroxidum,  A1(OH)3  =  77.54. 
Obtained  by  adding  ammonia  water  or  solution  of  sodium  carbonate 
to  solution  of  alum,  when  aluminum  hydroxide  is  precipitated  in  the 
form  of  a  highly  gelatinous  substance,  which,  after  being  well  washed, 
is  dried  at  a  temperature  not  exceeding  40°  C.  (104°  F.). 

2KA1(SO4)2  +  6NH4OH  =  K2SO4  +  3(NH4)2SO4  +  2A1(OH)3; 
2KA1(SO4)2  +  3Na2CO3  +  3H2O  =  K2SO4  +  3Na2SO4  +  3CO2  +  2A1(OH)S. 

When  aluminum  hydroxide  is  heated,  water  is  expelled  and  the 
oxide  is  left,  which  is  often  termed  alumina. 

The  usual  decomposition  between  a  soluble  carbonate  and  any  soluble  salt 
(provided  decomposition  takes  place  at  all)  is  the  formation  of  an  insoluble 
carbonate ;  according  to  this  rule,  the  addition  of  a  soluble  carbonate  to  alum 
should  produce  aluminum  carbonate.  The  basic  properties  of  aluminum 
oxide,  however,  are  so  weak  that  it  is  not  capable  of  uniting  with  so  weak  an 
acid  as  carbonic  acid,  and  it  is  for  this  reason  that  the  decomposition  takes 
place  as  shown  by  the  above  formula,  with  liberation  of  carbon  dioxide, 
while  the  hydroxide  is  formed.  (Other  metals,  the  oxides  of  which  have  weak 
basic  properties,  show  similar  reactions,  as,  for  instance,  chromium,  and  iron  in 
the  ferric  salts.) 

The  weak  basic  properties  of  aluminum  are  shown  also  by  the  fact  that  alu- 
minum sulphate,  chloride,  and  nitrate,  and  even  alum  itself,  have  an  acid 
reaction,  while  the  corresponding  salts  of  the  alkalies  or  alkaline  earths  are 
neutral. 

Aluminum  salts  in  solution  give  the  ion  Al*'%  which  forms  insoluble 
compounds  with  hydroxyl  ion  (OH)7,  carbonate  ion  COg",  phosphate  ion 
PO/X/,  sulphide  ion  S/x,  etc.  The  carbonate  and  sulphide  are  hydrolyzed 
with  elimination  of  CO2  and  H2S  respectively.  Aluminum  hydroxide  has 
such  weak  basic  properties  that  it  actually  shows  an  acid  character  toward  the 


288  METALS  AND   THEIR  COMBINATIONS. 

active  bases,  and  is  dissolved  by  them  to  form  compounds  called  aluminates. 
This  means  that  A1(OH)3  has  two  modes  of  ionization,  namely, 
A1(OH)3^±  Al—   f  3(OH)'; 
Al(OH),  ;±  A10/"  +  3H-. 

The  first  mode  takes  place  mainly,  and  in  the  presence  of  acids,  salts  are 
formed  thus  : 

Al-  -f-  3(OH)'  -f  3H-  +  3C1'  =  Al-  +  3C1'  +  3H2O. 

The  second  mode  of  ionization  takes  place  to  a  less  extent,  but  in  the  presence 
of  excess  of  alkalies  action  results  thus : 

A10S"'  -f  3H-  +  SNa-  +  3(OH)'  =  A1O3' "  -f  3Na'  +  3H,O. 
These  reactions  are  generally  written  thus : 

A1(OH)3  +  3HC1  =  A1C13  +  3H2O; 
A1(OH)3  -f  3NaOH  =  Na3AlO3  +  3H2O. 

The  compounds  of  the  form  Na3AlO3,  called  aluminates,  are  largely  hydrolyzed 
by  water  into  NaOH  and  A1(OH)3.  Hence,  an  excess  of  alkali  is  required  to 
dissolve  the  aluminum  hydroxide.  Ammonium  hydroxide  is  too  weak  a  base 
to  unite  with  it. 

Aluminum  hydroxide,  in  common  with  many  other  substances,  as  hydroxide 
of  iron,  chromium,  tin,  tannic  acid,  etc.,  has  the  power  of  uniting  with  dyes  and 
forming  colored  compounds  which  adhere  firmly  to  cotton  and  linen  fabrics. 
Such  substances  are  called  mordants  (meaning  biting),  and  without  their  use  it 
is  impossible  to  dye  cotton  and  linen  permanently  with  most  dyes.  The  insoluble 
compounds  of  dyes  with  mordants  are  called  lakes.  When  aluminum  hy- 
droxide is  to  be  the  mordant,  the  fabric  is  immersed  in  a  hot  solution  of  alum, 
aluminum  sulphate  or  acetate,  or  sodium  aluminate,  by  which  some  aluminum 
hydroxide,  formed  by  hydrolysis  of  the  compounds,  is  taken  up  by  the  fibres 
of  the  fabric.  The  latter  is  then  boiled  in  water  containing  the  dye,  which 
unites  with  the  mordant  in  the  fibres,  to  form  an  insoluble  permanent  color. 

Experiment  29.  Dissolve  10  grammes  of  sodium  carbonate  in  100  c.c.  of 
water,  heat  it  to  boiling,  and  add  to  it,  with  constant  stirring,  a  hot  solution, 
made  by  dissolving  10  grammes  of  alum  in  100  c.c.  of  water.  Wash  the  pre- 
cipitate first  by  decantation,  and  then  upon  a  filter,  until  the  washings  are  not 
rendered  turbid  by  barium  chloride.  Dry  a  portion  of  the  precipitate  at  a  low 
temperature,  and  use  as  aluminum  hydroxide.  Mix  a  small  quantity  of  the 
wet  precipitate  with  a  decoction  of  logwood  (made  by  boiling  about  0.2 
grammes  of  logwood  with  50  c.c.  of  water),  agitate  for  a  few  minutes,  and 
filter.  Notice  that  the  red  color  of  the  solution  has  entirely  disappeared,  or 
nearly  so,  in  consequence  of  the  combination  of  the  aluminum  hydroxide 
and  coloring  matter. 

Aluminum  sulphate,  Alumini  sulphas,  A12(SO4)3.16H2O  = 
625.93.  A  white  crystalline  powder,  soluble  in  about  its  weight 
_of  water,  obtained  by  dissolving  the  oxide  or  hydroxide  in  sulphuric 
acid  and  evaporating  the  solution  to  dryness  over  a  water-bath. 

2A1(OH)3  +  3H2S04  ==  A1.2(S04),  +  6H2O. 


ALUMINUM.  289 

Aluminum  chloride,  A1C13.  This  compound  is  of  interest  on  account  of 
being  the  salt  from  which  the  metal  was  formerly  obtained.  Most  chlorides 
may  be  formed  by  dissolving  the  metal,  its  oxide,  hydroxide,  or  carbonate  in 
hydrochloric  acid.  Accordingly  aluminum  chloride  may  be  obtained  in 
solution  : 

A1(OH)3  +  3HC1  =  A1C13  +  3H2O. 

On  evaporating  the  solution  to  dryness,  however,  and  heating  the  dry  mass 
further  with  the  view  of  expelling  all  water,  decomposition  takes  place,  hydro- 
chloric acid  escapes,  and  aluminum  oxide  is  left: 

2A1CL,  +  3H2O  =  A1203  -f  6HC1. 

Aluminum  chloride,  consequently,  cannot  be  obtained  in  a  pure  state  (free 
from  water)  by  this  process,  but  it  may  be  made  by  exposing  to  the  action  of 
chlorine  a  heated  mixture  of  aluminum  oxide  and  carbon.  Neither  carbon 
nor  chlorine  alone  causes  decomposition  of  the  aluminum  oxide,  but  by  the 
united  efforts  of  these  two  substances  decomposition  is  accomplished  : 

A12O3  f  3C  +  GC1  =  3CO  +  2A1CL,. 

Clay  is  the  name  applied  to  a  large  class  of  mineral  substances, 
differing  considerably  in  composition,  but  possessing  in  common  the 
two  characteristic  features  of  plasticity  and  the  predominance  of 
aluminum  silicate  in  combination  with  water.  A  white  clay,  known  as 
kaolin,  consists  chiefly  of  a  silicate  of  the  composition 


The  various  kinds  of  clay  have  been  formed  in  the  course  of  time  from  such 
double  silicates  as  feldspar  and  others,  by  a  process  which  is  partly  of  a 
mechanical,  partly  of  a  chemical  nature,  and  consists  chiefly  in  the  disintegra- 
tion of  rocks  and  a  removal  of  potassium  and  sodium  by  the  chemical  action  of 
carbonic  acid,  water,  and  other  agents. 

The  various  kinds  of  clay  are  used  in  the  manufacture  of  bricks,  earthenware, 
stoneware,  porcelain,  etc.  The  process  of  burning  these  substances  accom- 
plishes the  hardening  by  expelling  water  which  is  present  in  the  clay.  Pure 
clay  is  white  ;  the  red  color  of  the  common  varieties  is  due  to  the  presence  of 
ferric  oxide.  For  china  or  porcelain,  clay  is  used  containing  silicates  of  the 
alkalies  which,  in  burning,  melt,  causing  the  production  of  a  more  homoge- 
neous mass,  while  in  common  earthenware  the  pores,  produced  by  expelling 
the  moisture,  remain  unfilled. 

Glass  is  similar  in  composition  to  the  better  varieties  of  porcelain. 
All  varieties  of  glass  are  mixtures  of  fusible,  insoluble  silicates,  made 
by  fusing  silicic  acid  (white  sand)  with  different  metallic  oxides  or 
carbonates,  the  silicic  acid  combining  chemically  with  the  metals. 
Sodium  and  calcium  are  the  chief  metals  in  common  glass,  though 
potassium,  lead,  and  others  also  are  frequently  used.  Color  is  im- 
parted to  the  glass  by  the  addition  of  certain  metallic  oxides,  which 

19 


290  METALS  AND   THEIR   COMBINATIONS. 

have  a  coloring  effect,  as.  for  instance,  manganese  violet,  cobalt  blue, 
chromium  green,  etc. 

Cement  or  hydraulic  mortar  is  the  name  given  to  a  finely  powdered 
mineral,  consisting  chiefly  of  basic  silicates  of  lime  and  alumina,  and  having 
the  power  of  forming  an  insoluble  solid  mass  when  mixed  with  water.  Some 
native  limestones,  containing  also  magnesium  carbonate  and  aluminum  silicate, 
furnish  cement  after  being  heated  to  expel  water  and  carbon  dioxide.  Other 
cements  are  made  by  burning  mixtures  of  limestone  and  clay  of  a  suitable  com- 
position. The  slag  of  iron  furnaces  also  furnishes  the  material  for  cement. 

Ultramarine  is  a  beautiful  blue  substance,  found  in  nature  as  the  mineral 
"  lapis  lazuli"  which  was  highly  valued  by  artists  as  a  color  before  the  dis- 
covery of  the  artificial  process  for  manufacturing  it. 

Ultramarine  is  now  manufactured  on  a  very  large  scale  by  heating  a  mix- 
ture of  clay,  sodium  sulphate  and  carbonate,  sulphur,  and  charcoal  in  large 
crucibles,  when  decomposition  takes  place  and  the  beautiful  blue  compound 
is  obtained.  As  neither  of  the  substances  used  in  the  manufacture  has  a  ten- 
dency to  form  colored  compounds,  the  formation  of  this  blue  ultramarine  is 
rather  surprising,  and  the  true  chemical  constitution  of  it  is  yet  unknown. 

Ultramarine  is  insoluble  in  water  and  is  decomposed  by  acids  with  libera- 
tion of  hydrogen  sulphide,  which  shows  the  presence  of  sodium  sulphide.  A 
green  ultramarine  is  now  also  manufactured.  The  approximate  formula  of  the 
blue  compound  is  Na2S2.4NaAlSiO4. 

Tests  for  aluminum. 
(Use  about  a  5  percent,  solution  of  alum  or  aluminum  sulphate.) 

1.  To  the  solution  add  solution  of  potassium  or  sodium  hydroxide  : 
a  faintly  bluish-white  gelatinous  precipitate  of  aluminum  hydroxide, 
A1(OH)3,  is  produced.     The  physical  appearance  of  the  precipitate  is 
characteristic.     It   is   soluble  in   excess  of  the  alkali,   forming  an 
al-uminate,  thus  : 

A1(OH)3    +    3NaOH     =     Al(ONa)3    +     3H2O. 

This  shows  that  A1(OH)3  has  weak  acid  character  toward  strong  alka- 
lies.    It  is  reprecipitated  on  adding  ammonium  chloride  and  heating. 
Aluminum  hydroxide  is  soluble  in  acids,  even  acetic  acid. 

2.  To  the  solution  add  ammonia  water :  the  same  precipitate  as 
above  is  obtained,  but  it  is  insoluble  in  an  excess  of  the  reagent  (dif- 
ference from  zinc)  and  also  in  ammonium  chloride  solution  (difference 
from  magnesium). 

3.  A  solution  of   a  carbonate  produces  the  same  precipitate  as 
above,  with  liberation  of  carbon  dioxide,  not  very  noticeable  in  dilute 
solutions  (see  explanation  in  text). 


ALUMINUM.  291 

4.  Solution  of  ammonium  sulphide  produces  the  same  precipitate, 
with  generation  of  hydrogen  sulphide  : 

A12(S04)3  +  3(NH4)2S  +  6H20  =  2A1(OH),  +  3(NH4)2SO4  +  3H2S. 

5.  Solution  of  sodium  phosphate  produces  a  white  precipitate  of 
aluminum  phosphate,  A1PO4.4H2O,  soluble  in  mineral  acids,  but  not 
acetic,  and  in  fixed  alkalies  (difference  from  iron). 

6.  Heat  a  dry  aluminum  salt  on  charcoal  strongly  with  the  blow- 
pipe flame.     The  residue  is  aluminum  oxide,  which,  when  moistened 
with  solution  of  cobalt  nitrate  and  again  heated,  gives  a  blue  com- 
pound, cobalt  aluminate. 

Test  1  combined  with  Tests  5  and  6  are  conclusive. evidence  of  the 
presence  of  aluminum.  The  salts  are  white,  have  a  sweetish,  astringent 
taste,  are  acid  to  litmus,  and  decomposed  by  heat,  leaving  a  residue 
of  oxide. 

Cerium,  Ce  =  141.  This  element  occurs  in  nature  sparingly  in  a  few  rare 
minerals,  chiefly  as  silicate  in  cerite.  In  its  general  deportment  cerium  resem- 
bles aluminum.  Cerous  solutions  give  with  either  ammonium  sulphide  or 
ammonium  and  sodium  hydroxide,  a  white  precipitate  of  cerous  hydroxide, 
Ce2(OH)6.  Ammonium  oxalate  forms  a  white  precipitate  of  cerium  oxalate, 
ceriioxalas,  Ce2(C204)310H2O,  which  is  the  only  official  cerium  preparation. 
Cerium  oxalate  is  a  white,  granular  powder,  insoluble  in  water  and  alcohol, 
but  soluble  in  hydrochloric  acid.  Exposed  to  a  red  heat  it  is  decomposed  and 
converted  into  reddish-yellow  eerie  oxide.  If  this  oxide,  or  the  residue  obtained 
by  heating  any  cerium  salt  to  red  heat,  is  dissolved  in  concentrated  sulphuric 
acid,  and  a  crystal  of  strychnine  added,  a  deep  blue  color  appears,  which 
changes  first  to  purple  and  then  to  red.  The  official  cerium  oxalate  contains 
also  a  small  quantity  of  the  oxalates  of  didymiuin,  lanthanum,  and  other  rare 
earths. 

Monazite  sand,  found  in  North  Carolina  and  elsewhere,  contains,  besides 
cerite.  the  silicates  or  oxides  or  phosphates  of  other  earth  metals,  especially 
of  zirconium,  erbium,  and  thorium.  It  is  chiefly  the  oxide  of  thorium  which  is 
used  in  the  mantle  of  the  Welsbach  incandescent  burner,  on  account  of  the 
bright  white  light  which  this  oxide  emits  at  a  comparatively  low  temperature. 

QUESTIONS. — Mention  some  varieties  of  crystallized  aluminum  oxide  found 
in  nature  and  some  silicates  containing  it.  Give  the  general  formula  of  an 
alum,  and  mention  some  alums.  Which  alum  is  official,  how  is  it  made,  what 
are  its  properties,  and  what  is  it  used  for?  What  is  dried  alum,  and  how  does 
it  differ  from  common  alum?  How  is  aluminum  chloride  made,  and  how  ia 
the  metal  obtained  from  it?  State  the  properties  of  aluminum.  What  change 
takes  place  when  ammonium  hydroxide,  and  what  change  when  sodium  car- 
bonate is  added  to  a  solution  of  alum  ?  What  is  the  composition  of  earthen- 
ware, porcelain,  and  glass ;  how  and  from  what  materials  are  they  manufac- 
tured? What  is  ultramarine  ?  Give  tests  for  aluminum  compounds. 


292 


METALS  AND  THEIR  COMBINATIONS. 


Summary  of  analytical  characters  of  the  earth-metals  and 

chromium. 


Aluminum, 

Cerium. 

Chromium. 

Ammonium  sulphide  . 

White  precipitate. 

White  precipitate. 

Green  precipitate. 

Potassium  hydroxide  . 
Ammonia  water  .     .    . 

White  precipitate. 
Soluble  in  KOH. 
Not  re-precipitated 
by  boiling. 
White  precipitate. 

WThite  precipitate. 
Insoluble  in  KOH 

White  precipitate. 

Green  precipitate. 
Soluble  in  KOH. 
Re-precipitated 
by  boiling. 
Green  precipitate. 

Ammonium  carbonate 

White  precipitate. 

White  precipitate. 

Green  precipitate. 

27.     IRON.     (Ferrum.) 
Fe»  =  55.5. 

General  remarks  regarding-  the  metals  of  the  iron  group.  The 
six  metals  (Fe,  Co,  Ni,  Mn,  Cr,  Zn)  belonging  to  this  group  are  distin- 
guished by  forming  sulphides  (chromium  excepted)  which  are  insolu- 
ble in  water,  but  soluble  in  dilute  mineral  acids;  they  are,  conse- 
quently, not  precipitated  from  their  neutral  or  acid  solutions  by 
hydrogen  sulphide,  but  by  ammonium  sulphide  as  sulphides 
(chromium  as  hydroxide);  their  oxides,  hydroxides,  carbonates, 
phosphates,  and  sulphides  are  insoluble;  their  chlorides,  iodides, 
bromides,  sulphates,  and  nitrates  are  soluble  in  water. 

With  the  exception  of  zinc,  these  metals  are  magnetic ;  they  de- 
compose water  at  a  red  heat,  the  oxide  being  formed  and  hydrogen 
liberated;  in  dilute  hydrochloric  or  sulphuric  acid  they  dissolve 
with  formation  of  chlorides  or  sulphates  respectively,  and  liberation 
of  hydrogen. 

Zinc  is  constantly  bivalent,  nickel  is  usually  bivalent,  but  trivalent 
in  a  few  compounds,  cobalt  is  bi-  and  trivalent,  iron  and  chromium 
are  bi-,  tri-,  and  sexivalent,  manganese  is  bi-,  tri-,  sexi-,  and  septiva- 
lenf.  All  the  metals,  except  zinc,  form  several  oxides,  the  higher 
ones  of  which  have  acid  character,  as  iron  trioxide,  chromium  tri- 
oxide,  manganese  trioxide  and  heptoxide. 

Occurrence  in  nature.  Among  all  the  heavy  metals,  iron  is  both 
the  most  useful  and  the  most  widely  and  abundantly  diffused  in 
nature.  It  is  found,  though  usually  in  but  small  quantities,  in  nearly 
all  forms  of  rock,  clay,  sand,  and  earth ;  its  presence  in  these  being 


IRON.  293 

indicated  generally  by  their  color  (red,  reddish-brown,  or  yellowish- 
red),  as  iron  is  the  most  common  of  all  natural,  inorganic  coloring 
agents.  It  is  found  also,  though  in  small  quantities,  in  plants,  and 
in  somewhat  larger  proportions  in  the  animal  system,  chiefly  in  the 
blood.  In  the  metallic  state  iron  is  scarcely  ever  found,  except  in 
the  meteorites  or  metallic  masses  which  fall  occasionally  upon  our 
earth  out  of  space. 

The  chief  compounds  of  iron  found  in  nature  are : 

Hematite,  ferric  oxide,  Fe2O3. 

Magnetic  iron  ore,  ferrous-ferric  oxide,  FeO.Fe2O9. 

Spathic  iron  ore,  ferrous  carbonate,  FeCOs. 

Iron  pyrites,  bisulphide  of  iron,  FeS2. 

The  carbonate  and  sulphate  are  found  sometimes  in  spring  waters, 
which,  when  containing  considerable  quantities  of  iron,  are  called 
chalybeate  waters.  Finally,  iron  is  a  constituent  of  some  organic 
substances  which  are  of  importance  in  the  animal  system. 

Manufacture  of  iron.  There  is  no  other  metal  manufactured  in 
such  immense  quantities  as  iron,  the  use  of  which  in  thousands  of 
different  tools,  machines,  and  appliances  is  highly  characteristic  of 
our  present  age.  Iron  is  manufactured  from  the  above-named  oxides 
or  the  carbonate  by  heating  them  with  coke  and  limestone  in  large 
blast  furnaces,  which  have  a  somewhat  cylindrical  shape,  and  are 
constantly  fed  from  above  with  a  mixture  of  the  substances  named, 
while  hot  air  is  forced  into  the  furnace  through  suitable  apertures 
near  its  hearth.  The  chemical  change  which  takes  place  in  the  upper 
and  less  heated  part  of  the  furnace  is  a  deoxidation  of  the  iron  oxide 

by  the  carbon  : 

Fe2O3  +  30  ==  SCO  -f  2Fe 

The  heat  necessary  for  this  decomposition  and  fusion  of  the  re- 
duced iron  is  produced  by  the  combustion  of  the  fuel,  maintained  by 
the  oxygen  of  the  air  blown  into  the  furnace.  At  the  same  time  the 
lime  and  other  bases  combine  with  the  silica  contained  in  the  ore, 
forming  a  fusible  glass,  called  cinder  or  slag.  The  iron  and  slag 
collect  at  the  bottom  of  the  furnace,  where  they  separate  by  gravity, 
and  are  run  off  every  few  hours. 

Iron  thus  obtained  is  known  as  cast-iron,  or  pig-iron,  and  is  not 
pure,  but  always  contains,  besides  silicon  (also  sulphur,  phosphorus, 
and  various  metals),  a  quantity  of  carbon  varying  from  2  to  5  per 
cent.  It  is  the  quantity  of  this  carbon  and  its  condition  which  im- 
parts to  the  different  kinds  of  iron  different  properties.  Steel  contains 


294  METALS  AND  THEIR  COMBINATIONS. 

from  0.16  to  2  per  cent,,  wrought-  or  bar-iron  but  very  small  quanti- 
ties, of  carbon.  Wrought-iron  is  made  from  cast-iron  by  the  process 
known  as  puddling,  which  is  a  burning-out  of  the  carbon  by  oxida- 
tion, accomplished  by  agitating  the  molten  mass  in  the  presence  of 
an  oxidizing  flame.  Steel  is  made  either  from  cast-iron  by  partially 
removing  the  carbon,  or  from  wrought-iron  by  recombining  it  with 
carbon — i.  e.,  by  agitating  together  molten  wrought-  and  cast-iron  in 
proper  proportions. 

Properties.  The  high  position  which  iron  occupies  among  the  useful  metals 
is  due  to  a  combination  of  valuable  properties  not  found  in  any  other  metal. 
Although  possessing  nearly  twice  as  great  a  tenacity  or  strength  as  any  of  the 
other  metals  commonly  used  in  the  metallic  state,  it  is  yet  one  of  the  lightest, 
its  specific  gravity  being  about  7.7.  Though  being  when  cold  the  least  yield- 
ing or  malleable  of  the  metals  in  common  use,  its  ductility  when  heated  is  such 
that  it  admits  of  being  rolled  into  the  thinnest  sheets  and  drawn  into  the  finest 
wire,  the  strength  of  which  is  so  great  that  a  wire  of  one-tenth  of  an  inch  in 
diameter  is  capable  of  sustaining  TOO  pounds.  Finally,  iron  is,  with  the  ex- 
ception of  platinum,  the  least  fusible  of  all  the  useful  metals. 

For  certain  articles,  such  as  armor  plate,  rock  breakers,  lathe  tools,  etc.,  steel 
is  hardened  by  alloying  it  with  small  quantities  of  certain  other  metals,  chiefly 
with  chromium,  nickel,  or  manganese. 

Iron  is  little  affected  by  dry  air,  but  is  readily  acted  upon  by  moist  air,  when 
ferric  oxide  and  ferric  hydroxide  (rust)  are  formed. 

Hardening  and  tempering  steel.  Steel  contains  carbon  both  in  the  ele- 
mentary state  as  graphite,  and  chemically  combined  as  iron  carbide.  Within 
certain  limits  the  tenacity  of  the  metal,  and  its  hardness  after  having  been 
heated  and  suddenly  cooled,  bear  a  direct  ratio  to  the  amount  of  combined 
carbon.  The  more  of  the  latter  is  present  the  harder  is  the  steel  and  vice  versd. 

If  steel  be  heated  to  redness  and  suddenly  chilled  it  has  attained  its  maxi- 
mum hardness;  if,  however,  it  be  permitted  to  cool  slowly  after  heating,  it 
becomes  soft.  Any  degree  of  hardness  between  these  extremes  can  be  obtained 
by  the  process  known  as  tempering  or  "  letting  down."  It  consists  in  carefully 
reheating  the  previously  hardened  metal  to  a  certain  temperature  and  then 
plunging  it  into  cold  water.  To  the  experienced  worker  the  required  temper- 
ature is  indicated  by  a  series  of  colors  appearing  successively  on  the  surface  of 
the  steel.  These  colors  are  due  to  a  gradually  thickening  film  of  iron  oxides 
while  the  iron  softens.  The  colors  pass  successively  from  pale  yellow  through 
several  shades  of  darker  yellow  to  brown,  purple,  blue,  and  bluish  black.  The 
highest  temperature  gives  the  least  hardness  and  vice  versd. 

In  hardening  steel,  prior  to  tempering,  care  should  be  taken  not  to  injure 
the  metal  by  overheating,  which  causes  oxidation  of  the  carbon  and  blisters  the 
metallic  surface,  rendering  a  fine  temper  impossible.  In  tempering  small 
instruments  a  coating  of  some  material,  such  as  soap,  is  necessary  to  prevent 
oxidation  as  far  as  possible. 

Elasticity  and  tenacity  desired  for  specific  purposes,  as  in  the  case  of  springs, 
is  imparted  to  steel  by  hammering.  This  causes  a  condensation  of  the  particles 


IRON.  295 

and  the  conversion  of  the  crystalline  structure  to  a  fibrous  condition,  in  which 
state  steel  is  more  elastic,  tougher,  and  of  greater  tensile  strength. 

Iron  forms  two  series  of  compounds,  distinguished  as  ferrous  and 
ferric  compounds ;  in  the  former,  iron  is  bivalent,  in  the  latter, 
apparently  trivalent.  Almost  all  ferrous  compounds  show  a  tendency 
to  pass  into  ferric  compounds  when  exposed  to  the  air,  or  more  readily 
when  treated  with  oxidizing  agents,  such  as  nitric  acid,  chlorine,  etc. 
As  the  reaction  of  iron  in  ferrous  and  ferric  compounds  diifers  con- 
siderably, they  must  be  studied  separately.  Ferrous  oxide  and 
hydroxide  are  more  strongly  basic  than  ferric  oxide  and  hy- 
droxide. 

Reduced  iron,  Ferrum  reductum.  This  is  metallic  iron,  obtained 
as  a  very  fine,  grayish-black,  lustreless  powder  by  passing  hydrogen 
gas  (purified  and  dried  by  passing  it  through  sulphuric  acid)  over 
ferric  oxide,  heated  in  a  glass  tube  : 

FeA  +  6H  =  3H20  +  2Fe. 

The  official  article  should  have  at  least  90  per  cent,  of  metallic 
iron. 

Ferrous  oxide,  FeO  (Monoxide  or  suboxide  of  iron).  This  com- 
pound is  little  known  in  the  separate  state,  as  it  has  (like  most  ferrous 
compounds)  a  great  tendency  to  absorb  oxygen  from  the  air.  The 
ferrous  hydroxide,  Fe(OH)2,  may  be  obtained  by  the  addition  of  any 
alkaline  hydroxide  to  the  solution  of  any  ferrous  salt,  when  a  white 
precipitate  is  produced  which  rapidly  turns  bluish -green,  dark-gray, 
black,  and  finally  brown,  in  consequence  of  absorption  of  oxygen 
(see  Plate  I.,  2) : 

FeSO4  +  2NH.OH  =  (NH4)2SO4  +  Fe(OH)2; 
2Fe(OH)2  +  O  +  H20  =  Fe2(OH)6. 

The  precipitation  of  ferrous  hydroxide  is  not  complete,  some  iron 
always  remaining  in  solution. 

Ferrous  oxide  is  a  strong  base,  uniting  with  acids  to  form  salts, 
which  have  usually  a  palo-groen  color. 

Ferric  oxide,  Fe2O3.  A  reddish-brown  powder,  which  may  be 
obtained  by  heating  ferric  hydroxide  to  expel  water : 

2Fe(OH)3  =  Fe2O3  +  3K.O. 
It  is  a  feeble  base ;  its  salts  show  usually  a  brown  color. 


296  METALS  AND  THEIR  COMBINATIONS. 

In  the  preparation  of  fuming  sulphuric  acid  (which  see)  by  heating  ferrous 
sulphate  there  is  left  a  residue  of  ferric  oxide,  known  as  rouge,  which  is  used 
as  a  red  pigment  and  as  a  polishing  powder. 

4FeS04    +     H20     =     2Fe,O,    +     H2S04.SO3    4-     2SO2. 

A  specially  fine  variety  of  rouge  for  polishing  is  manufactured  by  heating 
ferrous  oxalate,  FeC2O4,  in  contact  with  the  air. 

Ferric  hydroxide,  Ferri  hydroxidum,  Fe(OH)3  =  106.14,  Is 
obtained  by  precipitation  of  ferric  sulphate  or  ferric  chloride  by  am- 
monium or  sodium  hydroxide  (see  Plate  I.,  3)  : 

Fe2(S04)3  +  6NH4OH  =  3[(NH4)2SOJ  -f  2Fe(OH)3. 

Precipitation  is  complete,  no  iron  remaining  in  solution  as  in  the 
case  of  ferrous  salts. 

Ferric  hydroxide  is  a  reddish-brown  powder,  sometimes  used  as 
an  antidote  in  arsenic  poisoning ;  for  this  purpose  it  is  not  used  in 
the  dry  state,  but  after  having  been  freshly  precipitated  and  washed, 
it  is  mixed  with  water,  and  this  mixture  used. 

Ferric  hydroxide  with  magnesium  oxide,  U.  S.  P.,  is  a  mixture  freshly  made, 
when  called  for,  by  adding  magnesia  to  a  solution  of  ferric  sulphate,  when 
magnesium  sulphate  and  ferric  hydroxide  are  formed;  the  two  substances  are 
not  separated  from  each  other,  the  mixture  being  intended  for  immediate 
administration  as  an  antidote  in  cases  of  arsenic  poisoning. 

Ferrous-ferric  oxide,  FeO.Fe2O3  (Magnetic  oxide).  This  com- 
pound, which  shows  strong  magnetic  properties,  has  been  mentioned 
above  as  one  of  the  iron  ores,  and  is  known  as  loadstone.  It  has  a 
metallic  lustre  and  iron-black  color,  and  is  produced  artificially  by 
the  combustion  of  iron  in  oxygen,  or  in  the  hydrated  state  by  the 
addition  of  ammonium  hydroxide  to  a  mixture  of  solutions  of  ferrous 
and  ferric  salts. 

Iron  trioxide,  FeO3.  Not  known  in  a  separate  state,  but  in  com- 
bination with  alkalies.  In  these  compounds,  called  ferrates,  FeO3 
acts  as  an  acid  oxide,  analogous  to  chromium  trioxide,  CrO3,  in  chro- 
mates.  The  composition  of  potassium  ferrate  is  K2FeO4. 

Ferrous  Chloride,  FeCl2  (Protochloride  of  iron),  is  obtained  as  a 
pale-green  solution  by  dissolving  iron  in  hydrochloric  acid : 
Fe  +  2HC1  =  FeCl2  +  2H. 

The  anhydrous  salt  cannot  be  obtained  by  evaporation  of  the  solu- 
tion, as  it  decomposes  ;  but  it  may  be  made  by  heating  iron  in  a  cur- 


IKON.  297 

rent  of  dry  hydrochloric  acid   gas.     The   solution  and  salt  absorb 
oxygen  very  readily  : 

3FeCl2  -f  O  =  FeO  +  2FeCl3. 

Ferric  chloride,  Perri  chloridum,  FeClr6H2O  =268.32  (Chlo- 
ride, sesqui-chloride,  or  perchloride  of  iron),  is  obtained  by  adding  to 
the  solution  of  ferrous  chloride  (obtained  as  mentioned  above)  hydro- 
chloric and  nitric  acids  in  sufficient  quantities,  and  applying  heat 
until  complete  oxidation  has  taken  place.  The  nitric  acid  oxidizes 
the  hydrogen  of  the  hydrochloric  acid  to  water,  while  the  chlorine 
combines  with  the  ferrous  chloride,  nitrogen  dioxide  being  formed 
also : 

3FeCl2  +  HNO8  +  3HC1  =  3FeCls  +  2H2O  +  NO. 

By  sufficient  evaporation  of  the  solution,  ferric  chloride  is  obtained 
as  a  crystalline  mass  of  an  orange-yellow  color;  it  is  very  deli- 
quescent, has  an  acid  reaction,  and  a  strongly  styptic  taste.  The 
water  of  crystallization  cannot  be  expelled  by  heat,  because  heat 
decomposes  the  salt,  free  hydrochloric  acid  and  ferric  oxide  being 
formed. 

Experiment  30.  Dissolve  by  the  aid  of  heat  1  gramme  of  fine  iron  wire  in 
about  4  c.c.  of  hydrochloric  acid,  previously  diluted  with  2  c.c.  of  water. 
Filter  the  warm  solution  of  ferrous  chloride,  mix  it  with  2  c.c.  of  hydrochloric 
acid,  and  add  to  it  slowly  and  gradually  about  0.6  c.c.  of  nitric  acid.  Evap- 
orate in  a  fume  chamber  as  long  as  red  vapors  escape ;  then  test  a  few  drops 
with  potassium  ferricyanide,  which  should  not  give  a  blue  precipitate ;  if  it 
does,  the  solution  has  to  be  heated  with  a  little  more  nitric  acid  until  the  con- 
version into  ferric  chloride  is  complete  and  the  potassium  ferricyanide  pro- 
duces no  precipitate.  Ferric  chloride  thus  obtained  may  be  mixed  with  4  c.c. 
of  hot  water  and  set  aside,  when  it  forms  a  solid  mass  of  FeCl3.6H2O.  How 
much  FeCl2,  how  much  FeCl3,  and  how  much  FeCl3.6H2O  can  be  obtained 
from  1  gramme  of  iron? 

Solution  of  ferric  chloride,  Liquor  ferri  chloridi.  This  is  a 
solution  in  water,  containing  29  per  cent,  of  the  anhydrous  ferric 
chloride.  It  is  a  reddish-brown  liquid  of  specific  gravity  1.315,  hav- 
ing the  taste  and  reaction  of  the  dry  salt.  This  solution,  mixed  with 
alcohol  in  the  proportion  of  35  to  65  parts  by  volume,  and  left  stand- 
ing in  a  closed  vessel  for  at  least  three  months,  forms  the  tincture  of 
ferric  chloride,  Tinctura  ferri  chloridi.  By  the  action  of  the  alcohol 
on  ferric  chloride  this  is  reduced  to  the  ferrous  state,  while  at  the 
same  time  a  number  of  other  compounds  are  formed,  imparting  to  the 
liquid  an  ethereal  odor. 

Solutions  of  ferric  salts  usually  have  a  brown  color  and  show  an  acid  reac- 
tion. This  is  due  to  the  partial  hydrolysis  of  the  salts,  forming  ferric  hydroxide 


298  METALS  AND  THEIR  COMBINATIONS. 

and  free  acid.  Addition  of  acid,  by  preventing  hydrolysis,  renders  the  solu- 
tions colorless  or  nearly  so.  Hydrolysis  is  increased  by  heating  the  solutions, 
hence  hot  ferric  solutions  have  a  deeper  color  than  cold  ones. 

Ferrous  salts  are  much  less  hydrolyzed  than  ferric  salts,  as  ferrous  iron  is  a 
stronger  base  than  ferric  iron.  They  also  are  not  as  acid  to  litmus  as  the 
ferric  salts. 

Dialyzed  iron  is  an  aqueous  solution  of  about  5  per  cent,  of  ferric  hydrox- 
ide with  some  ferric  chloride.  It  is  made  by  slowly  adding  ammonium  hy- 
droxide to  a  solution  of  ferric  chloride  as  long  as  the  precipitate  of  ferric 
hydroxide  formed  is  redissolved  in  the  ferric  chloride  solution,  on  shaking 
violently.  The  clear  solution  thus  obtained  is  placed  in  a  dialyzer  floating  in 
water  which  latter  is  renewed  every  day  until  it  shows  no  reaction  with  silver 
nitrate.  The  ammonium  chloride  passes  through  the  membrane  of  the  dialyzer 
into  the  water,  while  all  iroir  as  hydroxide  with  some  chloride,  is  left  in 
solution. 

The  combination  of  an  oxide  or  hydroxide  with  a  normal  salt  is  called 
usually  a  basic  salt  or  oxy-salt ;  dialyzed  iron  is  a  highly  basic  oxychloride 
of  iron. 

Ferrous  iodide,  Fel^  and  Ferrous  bromide,  FeBr2,  may  both  be 
obtained  by  the  action  of  iodine  and  bromine,  respectively,  on  iron  filings, 
when  combination  takes  place.  Both  salts  are  unstable,  absorbing  oxygen 
from  the  air  very  readily. 

Experiment  31.  Cover  some  fine  iron  wire  with  water,  heat  gently,  and  add 
iodine  in  fragments  as  long  as  the  red  color  of  iodine  disappears.  Notice  that 
the  iron  is  dissolved  gradually,  the  result  of  the  reaction  being  the  formation 
of  a  pale-green  solution  of  ferrous  iodide. 

Ferrous  sulphide,  FeS.  Easily  obtained  as  a  black,  brittle  mass, 
by  heating  iron  filings  with  sulphur,  when  the  elements  combine.  It 
is  used  chiefly  for  liberating  hydrogen  sulphide,  by  the  addition  of 
sulphuric  acid.  Iron  combines  with  sulphur  in  several  proportions; 
some  of  these  iron  sulphides  are  found  in  nature. 

Ferrous  sulphate,  Ferri  sulphas,  FeSO4.7H2O  =  276.O1  (Sul- 
phate of  iron,  Green  vitriol,  Copperas).     Obtained  by  dissolving  iron 
in  dilute  sulphuric  acid,  evaporating,  and  crystallizing : 
Fe  +  H2S04  =  2H  +  FeSO4. 

Also  obtained  as  a  by-product  in  some  branches  of  chemical  indus- 
try, and  by  heap-roasting  of  the  native  iron  sulphide : 

FeS2  +  60  =  FeS04  +  SO2. 

Ferrous  sulphate  crystallizes  in  large,  bluish-green  prisms ;  it  is 
soluble  in  water,  insoluble  in  alcohol.  Exposed  to  the  air,  it  loses 
water  of  crystallization  and  absorbs  oxygen. 


IKON.  299 

The  exsiccated  ferrous  sulphate,  U.  S.  P.,  is  made  by  expelling 
nearly  all  the  water  of  crystallization  by  heating  to  100°  C.  (212°  F.) ; 
the  granulated  (precipitated)  ferrous  sulphate  is  made  by  quickly 
cooling  a  hot  saturated  solution  of  ferrous  sulphate,  slightly  acidu- 
lated with  sulphuric  acid,  while  stirring,  when  ferrous  sulphate  sepa- 
rates as  a  crystalline  powder,  which  is  filtered,  washed  with  alcohol, 
and  dried. 

Experiment  32.  In  a  flask  put  10  c.c.  of  concentrated  sulphuric  acid  diluted 
with  40  c.c.  of  water,  add  iron  wire,  card  teeth,  or  nails,  in  portions,  until  the 
acid  is  exhausted,  as  seen  by  the  cessation  of  effervescence.  Gently  heating 
facilitates  the  action  at  the  end.  Note  the  bad  odor  of  the  hydrogen,  due  to 
impurities,  and  the  dark  flakes  of  carbon  in  the  solution.  Finally,  filter  the 
hot  solution  and  set  it  aside  to  crystallize.  If  crystals  do  not  form,  evaporate 
further. 

Ferrous  sulphate  readily  forms  double  salts  with  alkali  sulphates,  which  are 
not  efflorescent,  and  in  the  dry  state  are  less  readily  oxidized  than  ferrous  sul- 
phate. When  a  hot,  strong  solution  of  1  part  of  ammonium  sulphate  is  added 
to  a  similar  solution  of  2  parts  of  crystals  of  ferrous  sulphate,  on  cooling,  a 
salt  with  the  composition,  (NHJ2SO4.FeSO4.6H.20,  separates  (Mohr's  salt). 
This  is  often  used  when  a  stable  ferrous  salt  is  wanted. 

Ferric  sulphate,  Fe2(SO4)3.  The  solution  of  this  salt,  Liquor  ferri 
tersulphatis,  is  made  by  adding  sulphuric  and  nitric  acids  to  a  solution 
of  ferrous  sulphate  and  heating  : 

6FeS04  +  3H2S04  +  2HNO3  =  3[Fe2(SO4)3]  +  2NO  +  4H2O. 

The  action  of  nitric  acid  is  similar  to  that  described  above  under 
ferric  chloride.  The  hydrogen  of  the  sulphuric  acid  is  oxidized,  and 
the  radical  SO4  unites  with  the  ferrous  sulphate,  nitrogen  dioxide 
being  liberated. 

Experiment  33.  Dissolve  several  crystals  of  ferrous  sulphate  in  about  20  c.c. 
of  water,  add  about  5  c.c.  of  dilute  sulphuric  acid.  Warm  the  solution  and 
add  concentrated  nitric  acid,  in  drops,  until  the  dark  color  first  produced  sud- 
denly turns  to  reddish-brown.  Note  the  red  fumes  of  oxide  of  nitrogen 
escaping.  The  dark  color  is  due  to  the  union  of  nitric  oxide,  NO  (see  reaction 
above),  with  unoxidized  ferrous  sulphate  (see  test  2  for  nitric  acid).  Heat  the 
solution  to  expel  oxide  of  nitrogen  and  excess  of  nitric  acid.  Dilute  a  few 
drops  and  test  with  ferricyanide,  as  in  Experiment  30. 

Solution  of  ferric  sulphate  is  used  in  the  preparation  of  Ferric 
ammonium  sulphate,  Ferri  et  ammonii  sulphas,  FeNH4(SO4)2.12H2O 
(iron  alum,  or  ammonio-ferric  alum),  which  is  made  by  mixing  a  solu- 
tion of  ferric  sulphate  with  ammonium  sulphate  and  crystallizing. 
The  salt  has  a  pale  violet  color  and  is  readily  soluble  in  water. 


300  METALS  AND   THEIR  COMBINATIONS. 

Solution  of  ferric  subsulphate,  Liquor  ferri  subsulphatis 
(Mouses  solution).  This  is  a  solution  similar  to  the  preceding,  but 
contains  less  sulphuric  acid,  and  is,  therefore,  looked  upon  as  a  basic 
ferric  sulphate,  of  the  doubtful  composition  5[Fe2(SO4)3].Fe2(OH)6. 

Ferrous  carbonate,  PeCO3.  Occurs  in  nature;  maybe  obtained 
by  mixing  solutions  of  ferrous  sulphate  and  sodium  carbonate  or 
bicarbonate  : 

FeS04  +  2NaHC03  =  NaJSO,  -f  FeCO3  +  CO2  +  H2O. 

The  precipitate  is  first  nearly  white,  but  soon  assumes  a  gray  color 
from  oxidation.  The  saccharated  ferrous  carbonate,  U.  S.  P.,  is  made 
by  mixing  the  washed  precipitate  with  sugar,  and  drying.  The 
sugar  prevents,  to  some  extent,  rapid  oxidation.  The  preparation 
contains  15  per  cent,  of  ferrous  carbonate. 

Ferric  carbonate  does  not  exist,  the  affinity  between  the  feeble  ferric 
oxide  and  the  weak  carbonic  acid  not  being  sufficient  to  unite  them 
chemically. 

Ferrous  phosphate,  Fe3(PO4)2.  When  sodium  phosphate  is 
added  to  solution  of  ferrous  sulphate,  a  precipitate  of  the  composi- 
tion FeHPO4  is  formed : 

NajHPO^  +  FeSO4  =  FeHPO4  +  Na.jSO4. 

If,  however,  sodium  acetate  is  added,  a  precipitate  of  the  composi- 
tion Fe3(PO4)2  is  formed : 

3FeSO4  +  2N02HPO4  =  Fe3(PO4)2  +  2Na2SO4  -f  H2SO4. 

The  sulphuric  acid  liberated,  as  shown  in  this  formula,  decomposes 
the  sodium  acetate,  forming  sodium  sulphate  and  free  acetic  acid. 
Ferrous  phosphate  is  a  slate-colored  powder,  absorbing  oxygen 
readily,  becoming  darker  in  color. 

Ferric  phosphate,  FePO4,  may  be  obtained  from  ferric  chloride 
solution  by  precipitation  with  an  alkali  phosphate.  The  Soluble  ferric 
phosphate  and  the  Soluble  ferric  pyrophosphate  of  the  U.  S.  P.,  are 
scale  compounds.  (See  index.) 

Ferric  hypophosphite,  Ferri  hypophosphis,  Fe(H2PO2)3  = 
249.09  (Hypophosphite  of  iron).  It  is  obtained  by  adding  a  solution 
of  sodium  hypophosphite  to  a  solution  of  ferric  chloride  or  sulphate, 
free  from  excess  of  acid.  The  precipitate  is  filtered,  washed,  and  dried. 
It  is  a  grayish-white  powder,  slightly  soluble  in  water,  soluble  in 
hydrochloric  acid,  in  hypophosphorous  acid,  and  in  a  warm,  concen- 
trated solution  of  an  alkali  citrate. 


IRON. 


301 


Tests  for  iron. 


1.  Ammonium  sul- 
phide. 


2.  Hydrogen      sul- 
phide. 


3.  Ammonium,  so- 
dium, or  potas- 
sium hydroxide 


4.  Ammonium,  so- 
dium, or  potas- 
sium carbonate. 


5.  Alkali  phosphates 

or  arsenates 

6.  Potassium  ferro- 

cyanide. 

K4Fe(CN)6. 


7.  Potassium  ferri- 

cyanide. 

K6Fe2(CN)12. 

8.  Tannic  acid. 


9   Potassium  sul- 
phocyanate. 
KCNS. 


Ferrous  salts. 

(Use  FeSO4.) 

Black  precipitate  of   ferrous 
sulphide  (Plate  I.,  1). 
FeSO4  +  (NH4)2S  = 
(NH4)2SO4  +  FeS. 

No  change,  except  sometimes 
a  slight  black  discoloration, 
due  to  the  formation  of  a 
trace  of  FeS.  . 

White  precipitate  of  ferrous 
hydroxide  soon  turning 
green,  black,  and  brown. 
Precipitation  not  complete 
(Plate  I.,  2). 


2NaCl+    Fe(OH)2. 

White  precipitate  of  ferrous 
carbonate,  soon  turning 
darker. 

FeCl2  +  Na2CO8  = 
2NaCl  4-  FeCO3. 

Almost  white  precipitate,  soon 
turning  darker. 

Almost  white  precipitate, 
K2Fe[Fe(CN)6],  soon  turning 
blue  by  absorption  of  oxygen 
(Plate  I.,  4). 


Blue  precipitate  of  ferrous  ferri- 

cyanide,  or  Turnbull's  blue. 

3FeCl2  +  K6Fe2(CN)12  = 

6KC1    +  Fe8Fea(CN)lr 

No  change,  provided  oxidation 
of  the  ferrous  salt  has  not 
taken  place. 

As  above. 


Ferric  taltt. 

(UseFeCl,.) 

Black  precipitate  of  ferrous  sul- 
phide mixed  with  sulphur. 
2FeCl3  +  3[(NH4)2S]= 
6NH4C1  +  2FeS  +  S. 

Ferric  salts  are  converted  into 
ferrous  salts  with  precipita- 
tion of  sulphur. 


2FeCl.2  +  2HCl-f  S.. 

Keddish-brown   precipitate    of 
ferric  hydroxide.    Precipita- 
tion is  complete  (Plate  I.,  3). 
3(NH4OH)  = 
Fe(OH)3: 


Reddish-brown  precipitate  of 
ferric  hydroxide,  with  libera- 
tion of  carbon  dioxide  (Plate 
I.,  3). 

2FeCl3  -f  3Na2CO3  +  3H,O  - 
GNaCl  +  2Fe(OH)8  +  3CO2. 

A  yellowish-white  precipitate 
is  produced. 

Dark-blue  precipitate  of  ferric 
ferrocyanide,  or  Prussian  blue. 
Decomposed  by  alkalies ;  in- 
soluble in  acids  (Plate  I.,  5). 
3[K4Fe(CN)6]  = 
Fe43[Fe(CN)fl]. 

No  precipitate  is  produced,  but 
the  liquid  is  darkened  to  a 
greenish-brown  hue. 

A  dark  greenish-black  precipi- 
tate of  ferric  tannate  is  pro- 
duced. 

Deep  blood-red  solution  of  fer- 
ric sulphocyanate,  Fe(CNS)3 
(Plate  I.,  6). 


302  METALS  AND   THEIR   COMBINATIONS. 

Remarks  to  tests.  In  test  1  iron  in  the  ferric  state  is  too  weakly 
basic  to  form  ferric  sulphide,  but  in  the  ferrous  state  it  is  a  stronger 
base,  so  that  the  ferric  sulphide  breaks  down  at  the  moment  of  forma- 
tion to  ferrous  sulphide  and  sulphur.  If  ferrous  iron  were  as  weakly 
basic  as  aluminum  and  chromium,  no  precipitate  of  sulphide  would 
be  obtained. 

In  test  2  no  precipitate  is  formed,  because  of  the  acid  that  would 
be  set  free  by  the  reaction.  Ferric  salts  are  easily  reduced  to  ferrous 
salts,  and  vice  versa.  H2S  is  a  good  reducing  agent,  and,  when  acting 
as  such,  always  gives  a  precipitate  of  milk  of  sulphur,  which  easily 
passes  through  filter-paper  and  causes  annoyance  in  the  course  of 
qualitative  analysis. 

In  test  4  the  weak  basic  character  of  ferric  iron  and  the  resem- 
blance to  aluminum  and  chromium  is  again  shown. 

Tests  6,  7,  8,  and  9  are  not  only  delicate  and  decisive,  but  permit 
iron  in  either  state  to  be  detected  in  the  presence  of  the  other. 

Ferrous  compounds  form  the  divalent  ion  Fe",  which  is  pale-green,  and 
ferric  compounds  form  the  trivalent  ion  Fe*",  which  is  nearly  colorless.  The 
ionic  reactions  for  the  tests  for  iron  are  of  the  same  form  as  those  given  under 
the  tests  for  calcium.  In  test  2,  the  reduction  of  ferric  to  ferrous  salt  by  H2S 
is  expressed  by  the  ionic  equation : 

2Fe'"  +  6C1'  +  2H-  +  S"  =  2Fe"  +  2H*  +  6C1'  +  S. 
Each  of  the  iron  ions  loses  a  charge  of  electricity  and  the  sulphur  ion  loses 
its  two  charges,  which  mutually  neutralize  each  other,  and  elementary  sulphur 
is  precipitated.     The  reduction  with  ammonium  sulphide  is  represented  by  a 
similar  equation. 

The  formation  of  ferric  from  ferrous  chloride  is  expressed  thus : 

Fe"  +  2CP  +  Cl  =  Fe-  +  3C1'. 

The  iron  ion  assumes  another  positive  charge,  becoming  trivalent  ion,  and  the 
chlorine  atom  assumes  a  negative  charge,  becoming  chlorine  ion.  A  similar 
equation  holds  in  the  case  of  the  sulphate. 

QUESTIONS — Which  metals  belong  to  the  "  iron  group,"  and  what  are  their 
general  properties?  How  is  iron  found  in  nature,  and  what  compounds  are 
used  in  its  manufacture  ?  Describe  the  process  for  manufacturing  iron  on  a 
large  scale,  and  state  the  difference  between  cast-iron,  wrought-iron,  steel,  and 
reduced  iron.  State  the  composition  and  mode  of  preparation  of  ferrous  and 
ferric  hydroxides.  What  are  their  properties?  Describe  in  words  and  chem- 
ical symbols  the  process  for  making  ferric  chloride.  What  is  tincture  of  chlo- 
ride of  iron?  How  are  ferrous  iodide  and  bromide  made?  State  the  proper- 
ties of  ferrous  sulphate.  Under  what  other  names  is  it  known,  and  how  is  it 
made?  What  change  takes  place  when  soluble  carbonates  are  added  to  soluble 
ferrous  and  ferric  salts?  Mention  agents  by  which  ferrous  compounds  may  be 
converted  into  ferric  compounds,  and  these  into  ferrous  compounds.  Explain 
the  chemical  changes  taking  place.  Mention  tests  for  ferrous  and  ferric  com- 
pounds. 


IRON.    COBALT.    NICKEL, 


PLATE  I. 


Ferrous  sulphide,   precipitated    from 
ferrous  solutions  by  ammonium  sulphide. 


Ferrous  hydroxide,  passing  into 
ferric  hydroxide.  Ferrous  solutions  precipi- 
tated by  alkali  hydroxides. 


Ferric  hydroxide,   precipitated    from 
ferric  solutions  by    alkali  hydroxides. 


Ferrous    solutions,    precipitated   by 
potassium  ferrocyanide. 


Ferric     solutions,  precipitated     by 

potassium      ferrocyanide,  or,      Ferrous 

solutions      precipitated  by      potassium 
ferricyanide. 


Ferric  solutions,  treated  with  alkali 
sulphocyanates. 


Cobaltous  carbonate,  precipitated 
from  cobaltous  solutions  by  sodium 
carbonate. 


8 


Nickelous  carbonate,  precipitated 
from  nickelous  solutions  by  sodium 
carbonate. 


A  ftoen  &Co  LM  Babuiion. .  ltd 


MANGANESE-CHROMIUM— COBALT-NICKEL.  303 

28.    MANGANESE— CHROMIUM— COBALT— MCKEL. 

Manganese,  Mn  =  54.6.  The  principal  ore  is  the  dioxide  (black 
oxide  of  manganese,  pyrolusite),  MnOj,  which  is  always  accompanied 
by  iron  compounds.  Other  forms  occurring  in  nature  are  braunite, 
MnfO3,  hausmannite,  Mn^O^,  and  manganese  spar,  MnCO3.  In  small 
quantities  it  is  a  constituent  of  many  minerals. 

Metallic  manganese  resembles  iron  in  its  physical  and  chemical 
properties,  and  may  be  obtained  by  reducing  the  carbonate  with 
charcoal.  Manganese  is  darker  in  color  than  iron,  considerably 
harder,  and  somewhat  more  easily  oxidized.  Alloys  of  iron  and 
manganese  (20  to  80  per  cent.),  known  as  ferro-manganese,  are  used 
in  the  arts. 

Oxides  of  manganese.  Six  oxides  are  known.  MnO3  and 
Mn2O7  have  been  obtained  in  the  free  state,  but  they  are  very  unsta- 
ble, and  are  known  best  through  their  compounds : 

Manganoos  oxide  (monoxide  or  protoxide),  MnO. 

Manganous  manganic  oxide,  MnOMn,0^  =  Mn^O^ 

Manganic  oxide  (sesquioxide),  MiijQj. 

Manganese  dioxide  (binoxide,  peroxide,  black  oxide),  MnOr 

Manganese  trioxide,  MnQ,. 

Manganese  heptoxide,  Mn,Oj. 

The  chemical  behavior  of  these  oxides  varies  with  the  degree  of  oxidation, 
or,  in  other  words,  with  the  valence  of  the  manganese.  MnO  is  strongly  basic ; 
Mn,Oj  is  weakly  basic;  MnOj  has  feebly  acidic  character;  MnOs  is  more 
strongly  acidic,  being  the  anhydride  of  manganic  acid,  HjMnO4,  which  is 
known  only  in  its  salts ;  MnsOT  is  the  anhydride  of  permanganic  acid,  which 
is  known  in  aqueous  solution,  and  has  strong  acid  character. 

The  only  stable  salts  of  manganese  are  the  manganou.*  salts,  derived  from 
manganons  oxide,  MnO,  in  which  the  valence  of  manganese  is  2.  When  any 
oxide  of  manganese  (or  compounds  of  those  oxides  which  are  unstable  in  the 
free  state)  is  heated  with  an  acid,  a  manganous  salt  is  obtained.  In  this  action 
the  oxides  higher  than  MnO  give  off  oxygen,  or  oxidize  the  excess  of  acid  (see 
action  of  hydrochloric  acid  on  MnOj).  The  decomposition  of  potassium  per- 
manganate, which  has  been  used  hitherto  as  an  oxidizer,  may  now  be  explained. 
In  dilute  sulphuric  acid  solution  permanganic  acid  is  liberated  thus : 

2KMn04    +    H,SO4    =    K,SO4    +    2HMnO4. 

The  acid  is  stable  enough  when  nothing  else  is  present  that  can  be  oxidized, 
but  if  such  a  substance  is  added  the  permanganic  acid  breaks  down  to  mangan- 
ous oxide  and  oxygen : 

2HMnO4    =     HSO          +     MnA, 
Mn,O,         =     5O  +    2MnO, 

2MnO          +    2HjSO4    =    2MnSO4    +    2H,O. 

The  manganous  oxide  is  dissolved  by  the  acid  to  form  the  colorless  manganous 


304  METALS  AND   THEIR   COMBINATIONS. 

sulphate,  MnSO4.  The  oxygen  does  not  escape,  but  goes  to  the  reducing  com- 
pound. Conversely,  when  oxygen  is  forcibly  added  to  any  of  the  lower  oxides 
in  the  presence  of  alkalies,  the  MnO3  state  of  oxidation  is  attained,  that  is, 
salts  of  manganic  acid,  or  manganates,  are  produced,  as  K2MnO4,  from  which 
the  more  stable  permanganates  are  readily  obtained  (see  below). 

While  manganous  salts  are  stable  and  do  not  absorb  oxygen  like  ferrous 
salts,  manganous  hydroxide  and  carbonate  readily  absorb  oxygen  and  turn 
dark,  resembling  in  this  respect  iron. 

Manganous  oxide  is  a  greenish-gray  powder  obtainable  by  heating 
the  carbonate ;  or  as  a  nearly  white  hydroxide  by  precipitating  a 
manganous  salt  by  sodium  hydroxide.  It  is  a  strong  base,  saturating 
acids  completely,  and  forming  salts  which  have  generally  a  rose 
color  or  a  pale  reddish  tint. 

Manganese  dioxide,  MnO2,  is  by  far  the  most  important  com- 
pound of  manganese  found  in  nature,  as  it  is  largely  used  for  gener- 
ating chlorine  and  oxygen,  as  described  in  former  chapters. 

Precipitated  manganese  dioxide,  Mangani  dioxidum  praecipitatum, 
MnO.j  —  86.36,  is  obtained  by  pouring  a  mixture  of  ammonia  water  and 
hydrogen  peroxide  into  a  solution  of  manganese  sulphate,  when  manganese 
dioxide  mixed  with  some  oxide  is  precipitated  as  a  heavy,  black  powder : 

MnS04  +  2NH4OH  +  H2O2  =  (NH4)aSO4  +  2H2O  -f  MnO2. 

Experiment  34.  Mix  10  c.c.  of  5  per  cent,  ammonia  water  with  10  c.c.  of 
1.5  per  cent,  hydrogen  dioxide  solution,  and  pour  slowly  while  stirring  into 
20  c.c.  of  a  5  per  cent,  solution  of  manganous  sulphate.  Let  the  mixture 
stand  for  one  hour,  stirring  frequently.  Then  filter  and  wash  thoroughly  with 
hot  water,  let  drain,  and  dry.  Heat  some  of  the  precipitate  with  hydrochloric 
acid  in  a  test-tube  and  explain  the  result. 

Manganese  sulphate,  Mangani  sulphas,  MnSO4.4H2O  =  221.47, 
maybe  obtained  by  dissolving  the  oxide  or  dioxide  in  sulphuric  acid ; 
in  the  latter  case  oxygen  is  evolved  : 

MnO2  +  H,SO4  =  MnSO4  -f  H2O  -f  O. 

As  manganese  dioxide  generally  contains  iron  oxide,  the  solution  contains 
sulphates  of  both  metals.  By  evaporating  to  dryness  and  strongly  igniting, 
the  iron  salt  is  decomposed.  The  ignited  mass  is  now  lixiviated  with  water, 
and  the  filtered  solution  evaporated  for  Crystallization. 

It  is  an  almost  colorless,  or  pale  rose-colored  substance,  isomorphous  with 
the  sulphates  of  magnesium  and  zinc ;  it  is  easily  soluble  in  water. 

Manganese  hypophosphite,  Mangani  hypophosphis,  Mn(PH202)2.H,0 

=  201.54,  may  be  made  by  mixing  a  solution  of  1  part  of  calcium  hypo- 
phosphite  with  a  solution  of  1.31  parts  of  manganous  sulphate,  allowing 


MANGANESE— CHROMIUM-COBALT-NICKEL.  305 

the  precipitate  of  calcium  sulphate  to  settle,  and  evaporating  the  filtrate  to 
dryness.  It  is  a  pink  crystalline  powder,  permanent  in  the  air,  and  soluble  in 
6.6  parts  of  water.  Its  chief  use  is  as  a  constituent  of  compound  syrup  of 

hypophosphites. 

Potassium  permanganate,  Potassii  permanganas,  KMnO4  = 
156.98.  Whenever  a  compound  (any  oxide  or  salt)  of  manganese  is 
fused  with  alkali  carbonates  (or  hydroxides)  and  alkali  nitrates  (or 
chlorates)  the  manganese  is  converted  into  manganic  acid,  which 
combines  with  the  alkali,  forming  potassium  (or  sodium)  manganate: 
3MnOa  -f  3K8CO8  +  KC1O3  =  3K2MnO4  +  3CO?  +  KC1. 

The  fused  mass  has  a  dark-green  color,  and  when  dissolved  in 
water* gives  a  dark  emerald-green  solution,  from  which,  by  evapora- 
tion, green  crystals  of  potassium  manganate  may  be  obtained. 

The  green  solution  is  decomposed  easily  by  any  acid  (or  even  by 
water  in  large  quantity)  into  a  red  solution  of  potassium  perman- 
ganate and  a  precipitate  of  manganese  dioxide. 

3K2Mn04  +  2H2SO4  =  MnO2  +  2K2SO4  +  2KMnO4  +  2H2O. 

By  evaporation  and  crystallization  potassium  permanganate  is  ob- 
tained in  slender,  prismatic  crystals,  of  a  dark- purple  color,  and  a 
somewhat  metallic  lustre.  The  solution  in  water  has  a  deep  purple, 
or,  when  highly  diluted,  a  pink  color  (Plate  II.,  1).  It  is  a  power- 
ful oxidizing  agent,  and  an  excellent  disinfectant,  both  properties 
being  due  to  the  facility  with  which  a  portion  of  the  oxygen  is  given 
off  to  any  substance  which  has  affinity  for  it.  If  the  oxidation 
takes  place  in  the  absence  of  an  acid,  a  lower  oxide  of  manganese  is 
formed,  which  separates  as  an  insoluble  substance.  If  an  acid  is 
present,  both  the  potassium  and  manganese  combine  with  it,  forming 
salts,  thus  : 

2(KMnO4)  4-  6HC1  +  x  =  2KC1  +  2MnCl2  +  3H2O  -f  xO5. 

x  represents  here  any  substance  capable  of  combining  with  oxygen 
while  in  solution. 

Experiment  35.  Heat  in  an  iron  crucible  a  mixture  of  2  grammes  man- 
ganese dioxide,  2  grammes  potassium  hydroxide,  and  1  gramme  potassium 
chlorate,  until  the  fused  mass  has  turned  dark-green.  Dissolve  the  cooled 
mass  with  water,  filter  the  green  solution  of  potassium  manganate,  and  pass 
carbon  dioxide  through  it  until  it  has  assumed  a  purple  color,  showing  that 
the  conversion  into  permanganate  is  complete.  Notice  that  the  acidified  solu- 
tion is  readily  decolorized  by  ferrous  salts  and  other  deoxidizing  agents. 

Permanganic  acid,  HMn04,  can  now  be  obtained  in  solution  by  electrol- 
20 


306  METALS  AND   THEIR   COMBINATIONS. 

ysis  of  potassium  permanganate.     It  has  the  color  of  the  potassium  salt,  is 
stable,  and  from  it  the  permanganates  of  other  metals  may  be  made. 

Tests  for  manganese. 
(A  5  per  cent,  solution  of  manganous  sulphate  may  be  used.) 

1.  Ammonium  sulphide  produces  a  yellowish-pink  or  flesh-colored 
precipitate  of  hydrated  inanganous  sulphide,  MnS.H2O,  soluble  in 
acetic  and  in  mineral  acids  (Plate  II.,  2). 

2.  Ammonium  (or  sodium)  hydroxide  produces  a  white  precipi- 
tate of  manganous   hydroxide,  which   soon   darkens   by  absorption 
of  oxygen  (Plate  II.,  3)  and  dissolves  in  oxalic  acid  with  a  rose-red 
color.     The  presence  of  ammonium  salts  prevents  the  precipitation  of 
manganous  hydroxide  by  ammonia-water  (see  test  2  for  magnesium). 

3.  Sodium  (or  potassium)  carbonate  produces  a  nearly  white  pre- 
cipitate of  manganous  carbonate,  which  oxidizes  to  brown  manganic 
hydroxide. 

4.  Any  compound  of  manganese  heated  on  platinum  foil  with  a 
mixture  of  sodium  carbonate  and  nitrate  forms  a  bluish-green  mass, 
giving  a  green  solution  in  water,  which  turns  red  on  addition  of  an 
acid.     (See  explanation  above.) 

5.  Manganese   compounds  fused  with  borax  on  a  platinum  wire 
give  a  violet  color  to  the  borax  bead.     Only  a  very  small  quantity  of 
the  manganese  compound  should  be  used. 

6.  Heat  a  trace  of  manganese  compound  (not  the  dioxide)  with  about 
5  c.c.  of  dilute  nitric  acid  and  a  small  knife-pointful  of  red  oxide  of 
lead  (minium)  to  boiling,  dilute  with  water,  and   let  stand  to  settle. 
A  reddish-purple  color  of  permanganic  acid  will  be  seen.     This  is  a 
very  delicate  test. 

Tests  4,  5,  and  6  are  the  most  decisive  for  manganese  compounds. 
Test  2  is  also  characteristic.  Permanganate  is  usually  recognized  by 
its  color  and  action  on  reducing  agents.  Manganese  salts  are  neu- 
tral and  colorless,  or  light  red  to  pink. 

The  most  common  ions  of  manganese  are  the  divalent  Mn'  •  ions  of  the  man- 
ganous salts,  and  the  univalent  permanganate  ions  MnO/,  which  are  purple 
(see  page  200).  The  divalent  manganate  ions  MnO/x,  which  are  green,  exist 
only  in  neutral  or  alkaline  solutions.  In  acid  solutions  they  pass  into  MnO/ 
ions.  The  ionic  equations  in  the  tests  above  for  manganous  ions,  Mn'  *  are 
similar  to  those  given  under  the  tests  for  calcium. 

Chromium,  Cr  =  51.7.  Found  in  nature  almost  exclusively  as 
chromite,  or  chrome-iron  ore,  FeO.Cr2O3,  a  mineral  analogous  in 
composition  to  magnetic  iron  ore,  FeO.Fe?O?.  The  name  chromium. 


MA  NGANESE—  CHROMIUM-COB  A  LT- NICKEL.  307 

from  the  Greek  %po>/jLa  (chroma),  color,  was  given  to  this  metal  on 
account  of  the  beautiful  colors  of  its  different  compounds,  none  of 
which  is  colorless.  Chromium  forms  two  basic  oxides,  Chromous 
oxide,  CrO,  the  salts  of  which  are,  however,  very  unstable,  and  chromic 
oxide  or  chromium  sesquiozide,  Cr2O8,  and  an  acid  oxide,  chromium 
trioxide,  CrO8,  the  combinations  and  reactions  of  which  have  to  be 
studied  separately.  While  chromium  is  closely  allied  to  aluminum 
and  iron  on  one  side,  it  also  shows  a  resemblance  to  sulphur,  as  indi- 
cated by  the  trioxide,  CrO3,  and  the  acid,  H2CrO4,  which  are  analogous 
to  SO3  and  H2SO4.  Moreover,  the  barium  and  lead  salts  of  chromic 
and  sulphuric  acids  are  both  insoluble  in  water. 

Metallic  chromium  is  used  in  small  proportion  as  an  admixture  to  steel  to 
which  it  imparts  great  hardness. 

Potassium  dichromate,  Potassii  dichromas,  K2Cr2O7  =  292.28 
(Bichromate  or  red  chr ornate  of  potash).  This  salt  is  by  far  the  most 
important  of  all  chromium  compounds,  and  is  the  source  from  which 
they  are  obtained. 

Potassium  dichromate  is  manufactured  on  a  large  scale  by  expos- 
ing a  mixture  of  the  finely  ground  chrome-iron  ore  with  potassium 
carbonate  and  calcium  hydroxide  to  the  heat  of  an  oxidizing  flame 
in  a  reverberatory  furnace,  when  both  constituents  of  the  ore  become 
oxidized,  ferric  oxide  and  chromic  acid  being  formed,  the  latter 
combining  with  the  potassium,  forming  normal  potassium  chromate, 
K2Cr04. 

2(FeOCr203)  +  4K2CO3  +  7O  =  Fe2O3  +  4CO2  +  4(K2CrOJ. 

By  treating  the  furnaced  mass  with  water  a  yellow  solution  of 
potassium  chromate  is  obtained,  which,  upon  the  addition  of  sul- 
phuric acid,  is  decomposed  into  potassium  dichromate  and  potassium 

sulphate : 

2(K2CrO4)  +  H2SO4  =  K2Cr2O7  +  K2SO4  +  H2O. 

The  two  salts  may  be  separated  by  crystallization.  Potassium 
dichromate  forms  large,  orange-red,  transparent  crystals,  which  are 
easily  soluble  in  water;  heated  by  itself  oxygen  is  evolved,  heated 
with  hydrochloric  acid  chlorine  is  liberated,  heated  with  organic 
matter  or  reducing  agents  these  are  oxidized. 

Sodium  dichromate,  Na2Cr2O7.2H2O  (Bichromate  of  soda),  is  manufac- 
tured by  a  process  analogous  to  that  used  for  potassium  dichromate.  The 
crystallized  compound  resembles  the  potassium  salt,  but  dissolves  in  less  than 
its  own  weight  of  water.  The  crystals  being  deliquescent,  a  granulated  anhy- 
drous salt  which  is  but  slightly  hygroscopic,  is  also  manufactured,  and  has 
largely  replaced  the  use  of  potassium  dichromate. 


308  METALS  AND   THEIR   COMBINATIONS. 

Chromium  trioxide,  Chromii  trioxidum,  CrO3  =  99.34  (Chromic 
acid,  Chromic  anhydride),  is  prepared  by  adding  sulphuric  acid  to  a 
saturated  solution  of  potassium  dichromate,  when  chromium  trioxide 
separates  in  crystals : 

K20207  -f  H2S04  =  K2S04  +  H20  +  2CrO3. 

Thus  prepared,  it  forms  deep  purplish-red,  needle-shaped  crystals, 
which  are  deliquescent,  and  very  soluble  in  water;  it  is  destructive 
to  animal  and  vegetable  matter,  and  one  of  the  strongest  oxidizing 
agents ;  the  solution  in  water  has  strong  acid  properties,  but  neither 
chromic  nor  dichromic  acid  are  known  in  a  pure  state  as  an  aqueous 
solution  of  chromium  trioxide,  on  concentration  breaks  up  into  the 
oxide  and  water. 

Experiment  36.  Dissolve  a  few  grammes  of  potassium  dichromate  in  water 
and  add  to  4  volumes  of  the  cold  saturated  solution  5  volumes  of  strong  sul- 
phuric acid ;  chromium  trioxide  separates  on  cooling.  Collect  the  crystals  on 
asbestos,  wash  them  with  a  little  nitric  acid,  and  dry  them  by  passing  warm 
dry  air  through  a  tube  in  which  they  have  been  placed  for  this  purpose. 

Chromates  and  dichromates,  When  chromium  trioxide  is  dissolved  in 
water,  dichromic  acid  is  mainly  formed  thus  : 

200.  +  H20  =  H2Cr207, 

which  gives  the  ions  2H*  and  Cr2O7".     The  Cr2O7x/  ion  is  yellowish  red  in 
color.    There  is,  however,  a  slight  amount  of  chromic  acid  formed,  thus : 

Ci03  +  H20  =  H2CrO4, 

which  gives  the  ions  2H'  and  CrO4".    The  ion  CrO4"  is  yellow.    Chromic  acid 
is  known  through  its  salts,  the  chromates,  which  give  the  ion,  CrO/'. 

Potassium  and  sodium  chromate  in  solution  show  a  basic  reaction  which  is 
not  due  to  any  weak  acid  character  of  chromic  acid,  but  to  the  fact  that  chro- 
mates have  a  great  tendency  to  pass  to  salts  of  dichromic  acid.  They  are  de- 
composed to  some  extent  by  water,  thus : 

2K2CrO4  +  H20  ==  K2Cr2O7  +  2KOH. 

If  an  acid,  even  a  weak  one,  is  added  to  the  solution,  the  decomposition  be- 
comes practically  complete  by  the  removal  of  the  KOH  by  union  with  the 
acid.  The  color  changes  from  yellow  to  red,  and,  upon  concentration,  the 
rather  moderately  soluble  dichromate  crystallizes  out  in  the  case  of  the  potas- 
sium salt.  Potassium  dichromate  is  almost  neutral  in  reaction ;  it  is,  therefore, 
not  an  acid  chromate.  In  fact  acid  chromates  are  not  known  in  which  respect 
chromic  acid  diners  from  sulphuric  acid.  The  acid  salt  of  the  composition, 
KHCr04,  which  we  would  expect  to  be  formed  by  acidifying  a  solution  of  the 
chromate,  changes  at  once  into  the  salt  of  dichromic  acid,  thus : 
2KHCr04  =  K2Cr207  -f  H2O. 

Although  potassium  dichromate  contains  no  acid  hydrogen,  it  acts  essen- 
tially like  an  acid  salt  toward  alkalies.  When  potassium  hydroxide  is  added 


MANGANESE-CHROMIUM—COBALT-NICKEL.  309 

to  the  dichromate  the  solution  turns  yellow,  and  upon  evaporation  a  salt  of 
the  composition,  K2CrO4,  is  obtained.  The  reason  for  this  is  the  fact  that, 
although  the  dichromate  dissociates  in  the  main  into  2K'  and  Cr.,0/'  ions,  it 
also  dissociates  to  a  slight  extent,  thus  : 

K2Cr207  +  H2O  ^±  2K-  +  2H-  +  2CrO4". 
As  alkali  is  added,  the  hydrogen  ions  are  neutralized,  thus : 
2K-  +  2(OH)'  +  2H-  =  2K-  +  2H2O. 

To  keep  up  the  equilibrium,  more  H*  ions  and  CrO/'  ions  are  formed  from  the 
dichromate,  the  H*  ions  react  with  more  alkali,  etc.,  until  by  this  process  the 
dichromate  is  practically  all  converted  into  chromate.  This  change  is  usually 
represented  by  the  simple  equation : 

K.2Cr207  -f-  2KOH  =r  21^010,  +  H2O. 

Many  chromates,  for  example,  those  of  barium,  lead,  silver,  mercury,  etc.,  are 
insoluble  in  water  and  are  obtained  by  precipitation.  The  ionic  reaction  in 
the  case  of  barium  will  serve  to  illustrate  the  other  cases : 

2K-  -f  Cr04"  +  Ba-  *  +  2C1'  =  BaCiO4  +  2K>  +  2C1'. 

The  same  precipitates  result  when  a  solution  of  a  dichromate  is  used,  because 
it  contains  some  CrO/'  ions,  and  as  fast  as  these  are  removed  by  precipitation, 
others  are  produced  to  take  their  place  in  the  system.  But  the  precipitation 
of  the  metal  as  chromate  is  not  complete,  as  so.me  dichromate  of  the  metal  re- 
mains in  solution,  because  of  the  acid  that  is  liberated  in  the  reaction.  The 
essential  change  is  represented  by  the  simple  equation : 

K2Cr2O7  -f  2BaCl2  +  H2O  =  2BaCrO4  +  2KC1  +  2HC1. 

This  reaction  is  analogous  to  that  between  barium  chloride  and  potassium 
bisulphate : 

KHS04  +  BaCl2  =  BaSO4  +  KC1  +  HC1, 

with  the  difference  that  barium  sulphate  is  so  difficultly  soluble,  even  in  acids, 
that  precipitation  is  practically  complete,  whereas  the  chromates  are  more 
easily  soluble  in  acids,  and  precipitation  therefore  is  only  partial. 

Chromic  oxide,  Cr2O3  (Sesquioxide  of  chromium),  is  obtained  by 
heating  potassium  dichromate  with  sulphur,  when  potassium  sulphate 
and  chromic  oxide  are  formed  : 

K3Cr2O7  -1-  S  =  K2S04  +  Cr2O3. 

By  washing  the  heated  mass  with  water,  the  chromic  oxide  is  left 
as  a  green  powder,  which  is  used  as  a  green  color,  especially  in  the  manu- 
facture of  painted  glass  and  porcelain.  Prepared  by  this  method  at 
high  temperature  the  oxide  is  insoluble  in  acids,  but  when  obtained 
in  the  form  of  its  hydroxide  by  precipitation  it  is  soluble  in  acids 
forming  the  chromic  salts.  It  is,  therefore,  a  basic  oxide. 


310  METALS  AND  THEIR  COMBINATIONS. 

Chromic  hydroxide,  Cr(OH)3.  A  solution  of  potassium  dichro- 
rnate  may  be  deoxidized  by  the  action  of  hydrogen  sulphide,  sul- 
phurous acid,  alcohol,  or  any  other  deoxidizing  agent,  in  the  presence 
of  sulphuric  or  hydrochloric  acid  : 

K2Cr207  +  4H2S04  +  3H2S  =  K2SO4  -f  7H2O  +  3S  +  Cr2(SO4)3. 

As  shown  by  this  formula,  the  sulphates  of  potassium  and  chro- 
mium are  formed  and  remain  in  solution,  while  sulphur  is  precipi- 
tated, the  hydrogen  of  the  hydrogen  sulphide  having  been  oxidized 
and  converted  into  water. 

By  adding  ammonium  hydroxide  to  the  solution  thus  obtained, 
chromic  hydroxide  is  precipitated  as  a  bluish-green  gelatinous  sub- 
stance : 

Cra(S(Vs  +  6NH4OH  =  3(NH4)2SO4  -f  2Cr(OH)3. 

By  dissolving  this  hydroxide  in  the  different  acids,  the  various 
salts,  such  as  chloride,  CrCl3,  sulphate,  etc.,  are  obtained.  Chromic 
sulphate,  similar  to  aluminum  sulphate,  combines  with  potassium  or 
ammonium  sulphate  and  water,  forming  chrome  alum,  KCr(SO4)2. 
12H2O;  it  is  a  purple  salt,  and  is  isomorphous  with  other  alums. 

Perchromic  acid,  H2Cr2O8.  This  acid  is  of  interest  because  it  is  analogous 
to  persulphuric  acid,  H2S2O8,  and  is  formed  in  the  test  for  hydrogen  dioxide. 
The  ethereal  solution  is  obtained  when  an  acidified  saturated  aqueous  solution 
of  potassium  dichromate  is  shaken  with  ether  and  just  sufficient  hydrogen 
dioxide  solution  to  give  an  intense  blue  color.  Excess  of  hydrogen  dioxide 
must  be  avoided.  The  ethereal  solution  is  much  more  permanent  than  an 
aqueous  solution  of  the  acid.  When  it  is  cooled  to  — 20°  C.  (—4°  F.)  and 
treated  with  metallic  potassium,  a  purplish-black  precipitate  of  potassium  per- 
chromate,  K2Cr,,O8,  is  formed.  This  is  stable  only  at  low  temperature,  decom- 
posing at  ordinary  temperature  into  oxygen  and  potassium  chromate.  Several 
other  salts  have  been  prepared  ;  they  are  all  very  unstable. 

The  chemical  conduct  of  chromium,  according  to  the  degree  of  oxidation  or 
the  valence  of  the  metal,  is  like  that  of  manganese.  Chromous  salts,  corres- 
ponding to  the  oxide  CrO,  are  known,  but,  like  ferrous  salts,  they  are  very 
readily  oxidized  and  pass  to  the  stable  chromic  salts,  corresponding  to  the  oxide 
Cr2O3.  The  chromates  and  the  acid,  derived  from  the  oxide  CrO3,  although 
stable  when  alone  in  solution,  readily  give  up  oxygen  in  acid  solutions  to 
reducing  agents,  just  like  permanganates,  and  the  chromium  gives  salts  of  the 
lower  oxide,  Cr2O8,  which  are  green  : 

K2Cr207    +     H2S04      =       K2S04  +     H2Cr207, 

H2Cr2O7     ^     H2O          +       2CrO3 ;  2Cr03    =      Cr2O3  +  3O, 
Cr203        +    3H2S04    =      02(S04)3  +     3H2O. 


MANGA  NESE-  CJIR  OMIUM-  COB  A  LT- NICK  EL .  311 

Tests  for  chromium. 

a.   Of  chromates. 

(Use  the  reagent  solution  of  potassium  chromate,  K2CrO4.) 
.1.  Hydrogen  sulphide  added  to  an  acidified  warm  solution  of  a 
chromate  changes  the  red  color  into  green  with  precipitation  of  sulphur. 
The  solution  now  contains  chromium  in  the  basic  form.  (See  explana- 
tion above.)  (Plate  II.,  4.)  The  conversion  of  a  chromate  to  a 
chromium  salt  is  more  readily  accomplished  by  heating  the  chromic 
solution  with  alcohol  and  hydrochloric  acid;  the  alcohol  is  partly 
oxidized,  being  converted  into  aldehyde,  which  has  a  peculiar  but 
pleasant  odor. 

2.  Soluble  lead  salts  produce  a  yellow  precipitate  of  lead  chromate 
(chrome  yellow),  PbCrO4,  insoluble  in  acetic,  soluble  in  hydrochloric 
acid  and  in  sodium  hydroxide  (Plate  II.,  6)  : 

K2CrO4  +  Pb(NO3)2  =  PbCrO4  +  2KNO3. 

3.  Barium  chloride  produces  a  pale  yellow  precipitate  of  barium 
chromate,  BaCrO4 ;  insoluble  in  sodium  hydroxide. 

4.  Silver  nitrate  produces  a  dark-red  precipitate  of  silver  chromate, 
Ag2Cr04  (Plate  II.,  7). ' 

5.  Mercurous  nitrate  produces  a  red  precipitate  of  mercurous  chro- 
mate, Hg2CrO4  (Plate  II.,  8). 

6.  On   pouring   a   layer  of  ether   upon   a  solution  of  hydrogen 
dioxide,  adding  a  few  drops  of  potassium    dichromate  solution,  a 
little  sulphuric  acid,  and  shaking,  the  ether  assumes  a  blue  color,  due 
to  the  formation  of  unstable  perchromic  acid.     A  very  delicate  test. 

b.   Of  salts  of  chromium. 
(Use  a  5  per  cent,  solution  of  chrome-alum,  or  chromic  chloride,  CrCl3.) 

7.  To  the  solution  add  ammonium  hydroxide  or  ammonium   sul- 
phide :  in  both  cases  the  green  hydroxide  of  chromium,  Cr(OH)3,  is 
precipitated  (Plate  II.,  5).     Compare  with  aluminum. 

2CrCl3  +  3(NH4)2S  +  6H,O  =  6NH4C1  +  3H2S  +  2Cr(OH)3. 

8.  Potassium  or  sodium  hydroxide  causes  a  similar  green  precipi- 
tate of  chromic  hydroxide,  which   is  soluble  in   an  excess  of  the 
reagent,  but  is  re-precipitated  on  boiling  for  a  few  minutes. 

Ammonia  water  causes  precipitation  of  chromic  hydroxide,  but 
the  precipitate  is  nearly  insoluble  in  excess  of  the  reagent. 


312  METALS  AND   THEIR   COMBINATIONS. 

c.   Of  chromium  in  any  form. 

9.  Compounds  of  chromium,  when  mixed  with  sodium  (or  potas- 
sium) carbonate  and  nitrate,  give,  when  heated  upon  platinum  foil  or 
in  a  crucible,  a  yellow  mass  of  the  alkali  chromate. 

10.  Compounds  of  chromium  impart  a  green  color  to  the  borax 
bead.     Use  only  a  very  small  quantity  of  the  chromium  compound. 

Chromium  salts  have  a  green  or  violet  to  purple  color.  Solutions 
of  the  violet  salts  turn  green  when  heated.  They  are  acid  to  litmus, 
due  to  hydrolysis  in  solution.  Chromates  are  all  red  or  yellow,  and 
mostly  insoluble  in  water.  The  color  of  a  chromate  is  noticeable  in 
very  dilute  solution  (made  with  the  aid  of  an  acid  in  the  case  of  in- 
soluble salts). 

Cobalt  and  Nickel,  Co  =58.56,  Ni  =  58.3.  These  two  metals  show  much 
resemblance  to  each  other  in  their  chemical  and  physical  properties,  and  occur 
in  nature  often  associated  with  each  other  as  sulphides  or  arsenides. 

Both  metals  are  nearly  silver-white ;  the  salts  of  cobalt  show  generally  a  red, 
those  of  nickel  a  green  color.  The  solutions  of  both  metals  give  a  black  pre- 
cipitate of  the  respective  sulphides  on  the  addition  of  ammonium  sulphide. 
Ammonium  hydroxide  produces  in  solutions  of  cobalt  a  blue,  in  solutions  of 
nickel  a  green  precipitate  of  the  hydroxides,  both  of  which  are  soluble  in  an 
excess  of  the  reagent ;  potassium  or  sodium  hydroxide  produces  similar  pre- 
cipitates, which  are  insoluble  in  an  excess.  Sodium  carbonate  produces  in 
solutions  of  cobalt  a  violet,  and  in  solutions  of  nickel  a  green  precipitate  of  the 
respective  carbonates.  (Plate  I.,  7  and  8.) 

Cobalt  is  used  chiefly  when  in  a  state  of  combination  (for  coloring  glass  blue) ; 
nickel  when  in  the  metallic  state.  (German  silver  is  an  alloy  of  nickel,  copper, 
and  zinc.) 

29.     ZINC. 
Zn»  ==  64.9. 

Occurrence  in  nature.  Zinc  is  found  chiefly  either  as  sulphide 
(zinc-blende),  ZnS,  or  as  carbonate  (calamine),  ZnCO3 ;  it  occurs  also 
as  silicate,  H2Zn2SiO5,  and  as  oxide  in  combination  with  the  oxides 
of  iron  or  manganese. 

QUESTIONS.— How  is  manganese  found  in  nature?  Mention  the  different 
oxides  of  manganese.  What  is  the  dioxide  used  for  ?  What  is  the  color  of 
manganese  salts,  of  manganates,  and  of  permanganates?  How  is  potassium 
permanganate  made;  what  are  its  properties,  and  what  is  it  used  for?  Give 
tests  for  manganese.  State  composition  and  properties  of  potassium  dichro- 
mate.  How  is  chromium  trioxide  made ;  what  are  its  properties ;  what  is  it 
used  for ;  and  under  what  other  name  is  it  known  ?  By  what  process  may 
chromium  sesquioxide  be  converted  into  chromates  ?  What  is  the  composition 
of  the  oxide  and  hydroxide  of  chromium,  and  how  are  they  made?  Mention 
tests  for  chromates  and  chromium  salts. 


MANGANESE.    CHROMIUM. 


PLATE  II. 


Potassium  permanganate  solution, 
more  or  less  saturated.  Boraxbead  colored 
by  manganese. 


Manganous  sulphide,  precipitated 
from  manganous  solutions  by  ammonium 
sulphide. 


Manganous  hydroxide,  passing  into 
the  higher  oxides.  Manganous  solution* 
precipitated  by  alkali  hydroxides. 


Potassium  dichromate   solution  de- 
oxidized by  reducing  agents. 


Chromic  hydroxide,  precipitated 
from  chromic  solutions  by  alkali  hydrox- 
ides. 


Lead    chromate,     precipitated     from 
soluble  cbromates  by  lead  acetate. 


Silver    chromate,    precipitated    from 
neutral  chromates  by  silver  nitrate. 


Mercurous  chromate,  precipitated 
from  neutral  chromates  by  mercurous  bolu- 
tious. 


,  I.,rli  tiolniuorf, .  IM 


ZINC.  313 

Metallic  Zinc  is  obtained  by  heating  in  retorts  the  oxide  or 
carbonate  mixed  with  charcoal,  when  decomposition  takes  place. 
The  liberated  metal  is  vaporized,  and  distils  into  suitable  receivers, 
where  it  solidifies. 

Zinc  is  a  bluish-white  metal,  which  slowly  tarnishes  in  the  air, 
becoming  coated  with  a  film  of  oxide  and  carbonate ;  it  has  a  crys- 
talline structure  and  is,  under  ordinary  circumstances,  brittle  ;  when 
heated  to  about  130°-150°C.  (260°-302°  F.)  'it  is  malleable,  and 
may  be  rolled  or  hammered  without  fracture.  Zinc  thus  treated 
retains  this  malleability  when  cold ;  the  sheet-zinc  of  commerce  is 
thus  made.  When  zinc  is  further  heated  to  about  300°  C.  (572°  F.), 
it  loses  its  malleability  and  becomes  so  brittle  that  it  may  be  pow- 
dered ;  at  410°  C.  (760°  F.)  it  fuses,  and  at  a  bright- red  heat  it 
boils,  volatilizes,  and,  if  air  be  not  excluded,  burns  with  a  splendid 
greenish -white  light,  generating  the  oxide. 

Zinc  is  used  by  itself  in  the  metallic  state  or  fused  together  with 
other  metals  (German  silver  and  brass  contain  it) ;  galvanized  iron 
is  iron  coated  with  metallic  zinc. 

Zinc  combines-  with  mercury  forming  a  crystalline  amalgam  of  the  compo- 
sition Zn2Hg.  As  a  constituent  of  dental  amalgam  alloys  zinc  hastens  the 
setting,  aids  in  controlling  shrinkage  and  to  some  extent  prevents  discoloration. 
While  zinc  unites  with  tin  in  all  proportions  forming  excellent  alloys  for  dental 
dies,  it  is  not  suitable  for  alloying  with  lead. 

Zinc  is  a  bivalent  metal,  forming  but  one  oxide  and  one  series  of 
salts,  most  of  which  have  a  white  color, 

As  has  been  pointed  out  in  Chapter  24,  zinc  bears  a  close  chemical  relation- 
ship to  magnesium,  and  both  these  metals  resemble  cadmium  in  their  chemical 
properties.  In  fact,,  the  three  elements  magnesium,  zinc,  and  cadmium  form  a 
natural  group  similar  to  that  of  the  alkali  metals  or  the  alkaline  earth  metals. 

Zinc  oxide,  Zinci  oxiduni,  ZnO  =  80.78  (Flores  zinci,  Zinc-white), 
may  be  obtained  by  burning  the  metal,  but  if  made  for  medicinal 
purposes,  by  heating  the  carbonate,  when  carbon  dioxide  and  water 
escape  and  the  oxide  is  left : 

3[Zn(OH)2J.2ZnCO3  =  5ZnO  -f  2CO2  +  3H2O. 

It  is  an  amorphous,  white,  tasteless  powder,  insoluble  in  water, 
soluble  in  acids;  when  strongly  heated  it  turns  yellow,  but  on 
cooling  resumes  the  white  color. 

Zinc  hydroxide,  Zn(OH)2,  is  obtained  by  precipitating  zinc  salts 
with  the  hydroxide  of  sodium  or  ammonium ;  the  precipitate,  how- 
ever, is  soluble  in  an  excess  of  either  of  the  alkali  hydroxides. 


314  METALS  AND   THEIR   COMBINATIONS. 

Zinc  chloride,  Zinci  chloridum,  ZnCl2=  135.26.  Made  by  dis- 
solving zinc  or  zinc  carbonate  in  hydrochloric  acid  and  evaporating 
the  solution  to  dryness  : 

Zn  +  2HC1  =  ZnCl2  +  2H. 

It  is  met  with  either  as  a  white  crystalline  powder,  or  in  white 
opaque  pieces ;  it  is  very  deliquescent  and  easily  soluble  in  water 
and  alcohol;  it  combines  readily  with  albuminoid  substances;  it 
fuses  at  about  115°C.  (239°  F.),  and  is  volatilized,  with  partial 
decomposition,  at  a  higher  temperature. 

Liquor  zinci  chloridi,  U.  S.  P.,  is  an  aqueous  solution  of  zinc  chloride,  con- 
taining 50  per  cent,  of  the  salt. 

Zinc  oxychloride  is  used  extensively  for  dental  purposes,  and  is  made  by 
mixing  zinc  oxide  with  a  strong  solution  of  zinc  chloride.  At  first  a  plastic 
mass  forms,  which  rapidly  hardens.  The  proportions  in  which  the  two  sub- 
stances are  mixed  differ  widely,  the  weights  corresponding  all  the  way  from  3 
to  9  molecules  of  zinc  oxide  for  each  molecule  of  zinc  chloride.  Whether  or 
to  what  extent  the  oxychloride  of  zinc  is  a  true  chemical  compound  is  not 
known. 

Zinc  oxyphosphate  is  a  preparation  used  similarly  to  the  oxychloride.  It 
is  made  by  mixing  zinc  oxide  with  phosphoric  acid.  The  acid  used  is  either 
ortho-  or  metaphosphoric  acid,  or  a  mixture  of  both.  In  all  cases  a  zinc  phos- 
phate is  formed,  but  as  the  quantity  of  zinc  oxide  used  is  larger  than  needed 
for  saturating  the  acid  completely,  the  mass  as  used  by  dentists  is  generally  a 
mixture  of  zinc  phosphate  with  zinc  oxide. 

Zinc  bromide,  Zinci  bromidum,  ZnBr2  =  223.62.  Obtained 
analogously  to  the  chloride  by  dissolving  zinc  in  hydrobromic  acid  ; 
it  is  a  white  powder,  resembling  the  chloride  in  its  properties. 

Zinc  iodide,  Zinci  iodidum,  ZnI2  =  316.7.  The  two  elements 
zinc  and  iodine  combine  readily  when  heated  with  water ;  the  color- 
less solution  when  evaporated  to  dryness  yields  a  powder  whose 
physical  properties  resemble  those  of  the  chloride. 

Zinc  carbonate,  Zinci  carbonas  prsecipitatus,  2ZnCO3.3Zn(OH)2 
(Precipitated  carbonate  of  zinc).  Solutions  of  equal  quantities  of  zinc 
sulphate  and  sodium  carbonate  are  mixed  and  boiled,  when  a  white  pre- 
cipitate is  formed,  which  is  a  mixture  of  the  carbonate  and  hydroxide 
of  zinc,  corresponding  more  or  less  to  the  formula  given  above. 
5ZnSO4  +  5Na2CO3  +  3H2O  =  3CO2  +  5Na2SO4  -f  2(ZnCO3).3Zn(OH)2. 

Precipitated  zinc  carbonate  is  a  white,  impalpable  powder,  odorless 
and  tasteless,  insoluble  in  water,  soluble  in  acids  and  in  ammonia  water. 

Experiment  37.  Dissolve  10  grammes  of  the  zinc  sulphate  obtained  in  Experi- 


ZINC.  315 

ment  3,  in  about  200  c.c.  of  water,  heat  to  boiling,  and  add  slowly,  while  stir- 
ring, concentrated  solution  of  sodium  carbonate  until  precipitation  is  complete. 
After  the  precipitate  has  settled,  pour  off  the  liquid,  and  wash  the  former  sev- 
eral times  with  hot  water  by  decantation.  Then  filter  and  wash  the  precipitate 
again  several  times  with  hot  water,  drain,  and  dry. 

Heat  some  of  the  dried  zinc  carbonate  gradually  to  redness  in  a  porcelain 
crucible  with  the  cover  on.  What  is  formed?  What  color  has  it  while  hot? 
When  the  crucible  is  cold,  place  the  residue  in  a  tube  and  add  dilute  acid. 
Does  any  effervescence  take  place.  Write  reaction.  Compare  with  experi- 
ments 25  and  26. 

Zinc  sulphate,  Zinci  sulphas,  ZnSO4.7H2O  =  285.4  ( White  vit- 
riol), is  obtained  by  dissolving  zinc  in  dilute  sulphuric  acid : 
H2SO4  +  a:H2O  +  Zn  =  ZnSO4  +  xH2O  -f  2H. 

If  zinc  be  added  to  strong  cold  sulphuric  acid,  no  decomposition 
takes  place,  because  there  are  no  ions  present,  and  an  acid  does  not 
exhibit  acid  properties  unless  ions  *are  formed,  as  explained  in 
Chapter  15. 

Dilute  sulphuric  acid  scarcely  acts  on  pure  zinc,  but  addition  of  a  few  c.c.  of 
solution  of  cupric  sulphate  or  platinic  chloride  causes  brisk  action.  This  is 
due  to  the  deposition  of  the  copper  or  platinum  on  the  zinc,  thus  forming  an 
electric  couple,  whereby  solution  of  zinc  is  facilitated. 

Zinc  sulphate  forms  small,  colorless  crystals,  which  are  isomor- 
phous  with  magnesium  sulphate  ;  it  is  easily  soluble  in  water.  It  is 
so  much  like  magnesium  sulphate  in  appearance  that  it  is  sometimes 
taken  in  mistake  for  the  latter  salt.  The  tests  given  below  will  dis- 
tinguish between  the  two  salts. 

Antidotes.  Soluble  zinc  salts  (sulphate,  chloride)  have  a  poisonous  effect. 
If  the  poison  have  not  produced  vomiting,  this  should  be  induced.  Milk, 
white  of  egg,  or,  still  better,  some  substance  containing  tannic  acid  (with  which 
zinc  forms  an  insoluble  compound)  should  be  given. 


Tests  for  zinc. 
(Use  a  5  per  cent,  solution  of  zinc  sulphate.) 

1.  Add  to  the  solution  some  ammonium  sulphide.  A  white  precipi- 
tate of  zinc  sulphide,  ZnS,  is  produced,  which  is  soluble  in  mineral 
acids,  but  not  in  acetic  acid.  (Of  the  familiar  metals,  zinc  is  the  only 
one  whose  sulphide  is  white.) 

If  the  zinc  salt  is  not  pure,  the  sulphide  may  appear  more  or  less 
gray  instead  of  white  : 

ZnS04    +     (NH4)2S     =     (NH4)2S04    +     ZnS. 


316 


— 

1 


METALS  AND   THEIR   COMBINATIONS. 
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ZINC.  317 

2.  Hydrogen  sulphide  passed  into  the  solution  gives  a  partial  pre- 
cipitate of  zinc  sulphide  because  of  the  solvent  action   of  the  acid 
liberated.     In  the  presence  of  sodium  acetate,  however,  the  precipi- 
tate is  complete  because  of  the  liberation  of  acetic  acid,  in  which  the 
sulphide  is  insoluble : 

ZnS04  -I-  2Na(C2H302)  +  H2S  =  ZnS  +  Na2SO4  +  2H.C2H302. 

3.  Addition  of  caustic  alkali  or  ammonia  water  gives  a  white  pre- 
cipitate  of  zinc   hydroxide,  Zn(OH)2.     It  is  soluble  in  excess  of  the 
alkali,  forming  zincates : 

Zn(OH)2    +     2NaOH     =     Zn(ONa)2    +     2H20. 

The  hydroxide  is  also  soluble  in  excess  of  ammonia  water,  forming 
a  complex  compound,  Zn(NH3)4.(OH)2.  In  this  respect  zinc  differs 
from  magnesium.  The  ions  of  this  compound  are  Zn(NH3)4"  and 
2(OH)'. 

4.  Addition  of  a  solution  of  acarbftnate  or  phosphate,  gives  a  white 
precipitate  of  zinc  carbonate  or  phosphate  : 

ZnSO4    -f     Na2HPO4     =     ZnHPO4    +    Na2S04. 

Zinc  carbonate  is  soluble  in  excess  of  ammonium  carbonate. 

5.  Solution  of  potassium  ferrocyanide  gives  a  white  precipitate  of  zinc 
ferrocyanide.    (Distinction  from  magnesium  and  aluminum,  which  give 
no  precipitate.)     The    precipitate  is  Zn2Fe(CN)6,  and  is    difficultly 
soluble  in  hydrochloric  acid. 

Tests  1,  3,  and  5  together  are  conclusive  for  zinc  salts.  Practically 
all  the  compounds  of  zinc  are  colorless.  The  oxide,  carbonate,  phos- 
phate, ferrocyanide,  and  sulphide  are  insoluble  in  water;  the  chloride, 
bromide,  iodide,  nitrate,  sulphate,  and  acetate  are  soluble  in  water. 
These  are  the  common  salts.  The  soluble  zinc  salts  are  hydrolyzed 
somewhat  in  water,  and  therefore  show  an  acid  reaction.  This  explains 
the  solvent  action  of  a  zinc  chloride  solution  when  used  on  metal  sur- 
faces in  soldering.  The  coat  of  metallic  oxide  is  thus  removed. 

Zinc  forms  the  divalent  ion  Zn",  which  unites  with  acid  radicals  to  form 
the  zinc  salts.  The  ionic  equations  for  the  above  tests  are  of  the  same  form  as 
those  given  under  the  tests  for  calcium.  Zn(OH)2  has  weak  basic  properties, 
and  still  weaker  acid  properties.  Like  aluminum  and  chromium  hydroxides, 
it  is  slightly  soluble  and  ionizes  in  two  ways,  thus : 

Zn(OH)2  ^±  Zn"  4   2(OH)'. 
With  acids,  zinc  salts  are  formed  by  the  union  of  (OH)7  and  H*  ions  to  form  water. 

Also,  Zn(OH)2  ;±  Zn02"  4-  2H', 

and  with  considerable  excess  of  alkali  the  hydroxide  dissolves  to  form  zincates 


318  METALS  AND   THEIR   COMBINATIONS. 

by  the  union  of  H*  ions  with  (OH)'  ions  of  the  alkali.     The  equation  in  sim- 
ple form  is  written,  9 
Zn(OH)2  +  2XaOH  =  Na.2ZnO2  -f  2H2O. 

Cadmium,  Cd  =  111.6.  Found  in  nature  associated  (though  in  very  small 
quantities)  with  the  various  ores  of  zinc,  with  which  metal  it  has  in  common  a 
number  of  physical  and  chemical  properties.  Cadmium  differs  from  zinc  by 
forming  a  yellow  sulphide  (with  hydrogen  sulphide),  insoluble  in  diluted  acids. 
Cadmium  and  its  compounds  are  of  little  interest  here;  the  yellow  sulphide  is 
used  as  a  pigment,  the  sulphate  and  iodide  sometimes  for  medicinal  purposes. 

Cadmium  is  a  constituent  of  many  alloys  distinguished  by  very  low  fusing 
points. 

30.  LEAD -COPPER -BISMUTH. 

General  remarks  regarding  the  metals  of  the  lead  group.  The 
six  metals  belonging  to  this  group  (Pb,  Cu,  Bi,  Ag,  Hg,  and  Cd)  are 
distinguished  by  forming  sulphides  which  are  insoluble  in  water, 
insoluble  in  dilute  mineral  acids,  insoluble  in  ammonium  sulphide ; 
consequently  they  are  precipitated  from  neutral,  alkaline,  or  acid 
solutions  by  hydrogen  sulphide  or  ammonium  sulphide. 

The  metals  themselves  do  not  decompose  water  at  any  temperature, 
and  are  not  acted  upon  by  dilute  sulphuric  acid ;  heated  with  strong 
sulphuric  acid,  most  of  these  metals  are  converted  into  sulphates  with 
liberation  of  sulphur  dioxide ;  nitric  acid  converts  all  of  them  into 
nitrates  with  liberation  of  nitric  oxide. 

The  oxides,  iodides,  sulphides,  carbonates,  phosphates,  and  a  few  of 
the  chlorides  and  sulphates  of  these  metals  are  insoluble ;  all  the 
nitrates,  and  most  of  the  chlorides  and  sulphates  are  soluble. 

In  regard  to  valence,  they  show  no  uniformity  whatever,  silver 
being  univalent,  copper,  cadmium,  and  mercury  bivalent,  bismuth 
trivalent,  and  lead  either  bivalent  or  quadrivalent. 

Lead,  Pb11  =  2O5.35  (Plumbum).  This  metal  is  obtained  chiefly 
from  the  native  lead  sulphide  (galena),  PbS,  by  first  roasting  it, 
whereby  part  is  converted  into  oxide  and  sulphate.  By  heating  this 

QUESTIONS. — How  is  zinc  found  in  nature,  and  by  what  process  is  it  ob- 
tained? Mention  the  properties  of  metallic  zinc,  and  what  is  it  used  for? 
Mention  two  processes  for  making  zinc  oxide.  How  does  heat  act  on  zinc 
oxide?  Show  by  chemical  symbols  the  action  of  hydrochloric  and  sulphuric 
acids  on  zinc.  State  the  properties  of  chloride  and  of  sulphate  of  zinc.  AVhat 
is  white  vitriol?  Explain  the  formation  of  precipitated  zinc  carbonate,  and 
state  its  composition.  Mention  tests  for  zinc  compounds.  How  many  pounds 
of  crystallized  zinc  sulphate  may  be  obtained  from  21.7  pounds  of  metallic 
zinc?  i 


LEAD-COPPER-BISMUTH.  319 

mixture  with  undecomposed  sulphide  to  a  higher  temperature  lead  is 
formed,  thus : 

PbS   +   2PbO  ==   3Pb   +    S02  and   PbS   +    PbSO4  ==  2Pb   +   2SO2. 
Lead  owes  its  usefulness  in  the  metallic  state  chiefly  to  its  softness, 
fusibility,  and  resistance  to  acids,  which  properties  are  of  advantage 
in  using  it  for  tubes  or  pipes,  or  in  constructing  vessels  to  hold  or 
manufacture  sulphuric  acid. 

Lead  is  exceedingly  malleable  and  somewhat  ductile,  but  not  very  tenacious. 
It  is  a  constituent  of  many  alloys,  as  for  instance  of  type  metal,  britannia  metal, 
shot,  etc.  Common  solder  is  an  alloy  of  equal  weights  of  lead  and  tin.  The 
noble  metals  are  rendered  brittle  and  unworkable  when  alloyed  with  even  a 
small  quantity  of  lead. 

Experiment  38.  Dissolve  1  gramme  of  lead  acetate  or  lead  nitrate  in  about 
200  c.c.  of  water,  suspend  in  the  centre  of  the  solution  a  piece  of  metallic  zinc, 
and  set  aside.  Notice  that  metallic  lead  is  deposited  slowly  upon  the  zinc  in  a 
crystalline  condition,  while  zinc  passes  into  solution,  which  may  be  verified  by 
analytical  methods.  The  chemical  change  taking  place  is  this : 

Pb(N03)2     +     Zn  Zn(N03)2    +     Pb. 

Electrolytic  solution  tension.  The  precipitation  of  lead  from  solution 
by  zinc  in  the  experiment  above  is  represented  by  the  ionic  equation : 

Zn  +  Pb"  +  2NO3'  =  Zn"  +  2NO3'  +  Pb. 

The  lead  ions  lose  their  charges  to  zinc  which  becomes  ionic,  while  metallic 
lead  is  precipitated.  This  action  is  pretty  much  like  the  liberation  of  hydrogen 
from  acids  by  some  metals : 

Zn  +  2H*  +  SO4"  =  Zn"  +  SO4"  -f  H2. 

The  explanation  of  this  type  of  chemical  change  is  found  in  the  theory  of  elec- 
trolytic solution  tension  proposed  by  Nernst.  According  to  this,  a  metal  when 
immersed  in  water  or  a  solution  sends  some  positive  ions  into  the  solution,  and 
itself  assumes  negative  charges  of  electricity.  This  proceeds  to  a  point  where 
the  metal  is  sufficiently  charged  negatively  that  it  attracts  its  positive  ions  at 
the  same  rate  at  which  they  tend  to  be  given  off  from  the  metal.  An  equilib- 
rium between  the  two  tendencies  is  reached.  The  tension  or  pressure  that 
drives  the  ions  into  the  solution  differs  for  different  metals,  the  order  of  decrease 
being  the  same  as  the  order  in  the  electrochemical  series  of  the  metals  (page 
198).  Any  metal  in  the  series  has  a  higher  tension  than  those  following,  and 
will  displace  them  from  solutions  of  their  salts,  but  not  vice  versa.  Zinc  has 
a  much  greater  solution  tension  than  lead.  When  it  is  placed  in  the  lead  solu- 
tion, it  acquires  a  greater  negative  charge  of  electricity  than  does  a  piece  of 
lead  when  it  is  placed  in  a  solution.  The  result  is  that  the  lead  ions  are 
attracted  to  the  zinc  and  discharged,  and  metallic  lead  is  deposited.  This 
process  continues  until  all  the  lead  has  been  deposited  from  the  solution,  which 
then  contains  an  equivalent  amount  of  zinc  salt. 

Lead  oxide,  Plumbi  oxidum,  PbO  =  221.23  (Litharge).  Obtained 
by  exposing  melted  lead  to  a  current  of  air,  when  the  metal  is 


320  METALS  AND   THEIR   COMBINATIONS. 

gradually  oxidized  with  the  formation  of  a  yellow  powder,  known 
as  massicot;  at  a  high  temperature  this  fuses,  forming  reddish-yellow 
crystalline  scales,  known  as  litharge  ;  by  heating  still  further  in  con- 
tact with  air,  a  portion  of  the  oxide  is  converted  into  dioxide  (or 
peroxide),  PbO2,  and  a  red  powder  is  formed,  known  as  red  lead  (or 
minium),  which  probably  is  a  mixture  (or  combination)  of  oxide  and 
dioxide  of  lead,  PbO2(PbO)2. 

Lead  oxide  is  used  in  the  manufacture  of  lead  salts,  lead  plaster, 
glass,  paints,  etc. 

Nitric  acid  when  heated  with  red  lead  combines  with  the  oxide, 
while  lead  dioxide,  PbO2,  is  left  as  a  dark-brown  powder,  which,  on 
heating  with  hydrochloric  acid,  evolves  chlorine  (similar  to  man- 
ganese'dioxide).  Lead  dioxide  is  a  conductor  of  electricity,  differ- 
ing thus  from  most  oxides. 

Accumulator  or  storage  battery.  This  consists  of  two  sets  of  lead 
plates  made  in  the  form  of  gratings.  One  set,  which  are  all  connected,  have 
the  spaces  in  the  gratings  filled  up  with  spongy  lead ;  the  other  set,  likewise 
connected,  are  filled  up  with  lead  dioxide.  When  the  plates  are  dipped  into 
dilute  sulphuric  acid  they  show  a  difference  of  potential,  and  when  connected 
a  current  flows.  When  in  action  or  discharging,  the  SO/'  ions  of  the  sul- 
phuric acid  are  attracted  to  the  plates  filled  with  spongy  lead,  give  up  their 
negative  charges  to  the  plate,  and  form  lead  sulphate.  The  H*  ions  of  the  acid 
pass  to  the  plates  filled  with  PbO2,  give  up  their  positive  charges,  and  reduce 
PbO2  to  PbO,  which  combines  with  sulphuric  acid  and  forms  lead  sulphate. 
The  current  flows  in  the  outside  circuit  from  the  plates  filled  with  PbO2  to  the 
plates  filled  with  spongy  lead,  and  has  a  voltage  of  about  2.  Both  plates  ulti- 
mately become  filled  with  PbSO4,  and  the  battery  then  is  exhausted.  Sul- 
phuric acid  is  removed  from  the  solution,  and  the  specific  gravity  of  the  latter 
falls.  By  this  means  one  can  tell  when  the  battery  is  approaching  exhaustion. 

Charging  the  battery  consists  in  restoring  the  plates  to  their  original  state, 
and  is  accomplished  bypassing  a  current  from  a  dynamo  through  it  in  a  direc- 
tion opposite  to  that  of  the  current  produced  by  the  battery.  By  this  action 
electrical  energy  is  stored  up  in  the  battery  as  chemical  energy,  which  is  given 
back  again  as  electrical  energy  when  the  battery  is  discharged.  When  the 
dynamo  current  passes,  H*  ions  of  the  acid  solution  pass  to  the  plates  originally 
filled  with  lead,  and  form  sulphuric  acid  with  SO/X  ions  of  the  lead  sulphate, 
leaving  the  plate  finally  filled  with  reduced  spongy  lead.  At  the  same  time, 
SO4X/  ions  of  the  acid  solution  pass  to  the  other  plates,  where  they  are  dis- 
charged and  enter  into  reaction  with  the  lead  sulphate  in  the  plates,  thus  : 

PbS04  +  SO,  -f  2H20  =  PbO2  +  2H2S04. 

All  the  lead  sulphate  is  ultimately  converted  into  lead  dioxide,  and  this  set  of 
plates  are  restored  to  the  original  state.  All  the  sulphuric  acid  is  restored  to 
the  liquid,  and  the  battery  is  ready  for  use.  The  changes  involved  in  the  com- 
plete cycle  may  be  written  in  one  equation,  thus: 

«—  discharging. 

2PbS04  -(-  2H20  ±^  Pb  +  2H2S04  -f  PbO2. 
charging  — * 


LEAD— COPPER— BISMUTH.  321 

Lead  nitrate,  Plumbi  nitras,  Pb(NO3)2  —  328.49.  Obtained  by 
dissolving  the  oxide  in  nitric  acid : 

PbO  +  2HN03  =  H20  +  Pb(N03)2. 

Lead  nitrate  is  the  only  salt  of  lead  (with  a  mineral  acid)  which  is 
easily  soluble  in  water ;  it  has  a  white  color,  and  a  sweetish,  astrin- 
gent, and  afterward  metallic  taste.  It  is  insoluble  in  strong  nitric 
acid ;  hence  lead  is  insoluble  in  this  acid. 

Experiment  39.  Heat  30  c.c.  of  dilute  nitric  acid,  but  not  to  the  boiling- 
point,  and  dissolve  in  it,  with  stirring,  small  portions  of  lead  oxide,  until  no 
more  is  taken  up.  Filter  the  solution  if  necessary,  and  let  it  cool  to  crystallize. 
If  no  crystals  form,  concentrate  further.  The  crystals  are  octahedra.  Examine 
their  appearance  and  form.  Which  one  of  the  methods  of  forming  salts  does 
this  experiment  illustrate  ? 

Heat  some  of  the  dried  and  powdered  crystals  in  a  porcelain  crucible  mod- 
erately. Note  the  brown  fumes  of  nitrogen  tetroxide  and  residue  of  brown  lead 
oxide,  which  becomes  yellow  on  cooling.  This  experiment  illustrates  the 
instability  of  most  nitrates  when  heated,  and  the  method  by  which  some  oxides 
are  obtained : 

Pb(N03)2     =     PbO     +     N204    +     O. 

Lead  carbonate,  PbCO3,  occurs  in  nature  as  the  mineral  cerussite, 
and  may  be  obtained  by  precipitation  of  a  lead  acetate  solution  with 
sodium  bicarbonate.  While  this  normal  salt  is  scarcely  used,  the  basic 
lead  carbonate  or  white  lead  of  the  approximate  composition  2PbCO3. 
Pb(OH)2  is  used  very  largely  as  a  constituent  of  paints.  It  is  man- 
ufactured on  a  large  scale  directly  from  lead,  by  exposing  it  to  the 
simultaneous  action  of  air,  carbon  dioxide,  and  vapors  of  acetic  acid. 
The  latter  combines  with  the  lead,  forming  a  basic  acetate,  which  is 
converted  into  the  carbonate  (almost  as  soon  as  produced)  by  the 
carbon  dioxide  present. 

The  action  of  acetic  acid  on  lead  or  lead  oxide  will  be  considered 
in  connection  with  acetic  acid. 

Lead  carbonate  is  a  heavy,  white,  insoluble,  tasteless  powder ;  the 
white-lead  of  commerce  frequently  is  found  adulterated  with  barium 
sulphate,  gypsum  or  lead  sulphate. 

Lead  iodide,  Plumbi   iodidum,  PbI2  =  457.15.     Made  by  adding 
solution  of  potassium  iodide  to  lead  nitrate  (Plate  III.,  6) : 
Pb(NO3)2  +  2KI  =  2KNOS  +  PbI2. 

It  is  a  heavy,  bright  yellow,  almost  insoluble  powder,  which  ma/ 
be  distinguished  from  lead  chromate  by  its  solubility  in  ammonium 
chloride  solution  on  boiling,  lead  chromate  being  insoluble  in  this 
solution. 

21 


322  .METALS  AND   THEIR  COMBINATIONS. 

Poisonous  properties  and  antidotes.  Compounds  of  lead  are  directly 
poisonous,  and  it  happens,  not  infrequently,  that  water  passing  through  leaden 
pipes  or  collected  in  leaden  tanks  becomes  contaminated  with  lead.  Water 
free  from  air  and  salts  scarcely  acts  on  lead ;  but  if  it  contain  air,  oxide  of  lead 
is  formed,  which  is  either  dissolved  by  the  water  or  is  decomposed  by  the 
nitrates  or  chlorides  present  in  the  water,  the  soluble  nitrate  or  chloride  of  lead 
being  formed. 

If  the  water  contains  carbonates  and  sulphates,  however,  these  will  form 
insoluble  compounds,  producing  a  film  or  coating  over  the  lead,  preventing 
further  contact  with  the  water.  Rain  water,  in  consequence  of  its  containing 
atmospheric  constituents,  and  no  sulphates,  acts  as  a  solvent  on  lead  pipe ; 
spring  and  river  waters  generally  do  not. 

Water  containing  lead  will  show  a  dark  color  on  passing  hydrogen  sulphide 
through  it ;  if  the  quantity  present  be  very  small,  the  water  should  be  evapo- 
rated to  ^  or  even  -^  of  its  original  volume  before  applying  the  test. 

The  constant  handling  of  lead  compounds  is  one  of  the  causes  of  lead 
poisoning  (painters'  colic).  As  an  antidote,  mangesium  sulphate  should  be 
used,  which  forms  with  lead  an  insoluble  sulphate ;  the  purgative  action  of 
magnesia  is  also  useful.  (In  lead  works  workmen  often  drink  water  containing 
a  little  sulphuric  acid.) 


Tests  for  lead. 
(Use  a  5  per  cent,  solution  of  lead  acetate  or  lead  nitrate.) 

1.  Hydrogen  sulphide  or  ammonium  sulphide  added  to  the  solution 
produces  a  black  precipitate  of  lead  sulphide  (Plate  III.,,   1),  insol- 
uble in  dilute  acids  or  alkalies.     A  very  delicate  reaction  : 

Pb(N03)2    +    H2S  PbS    +    2HN03. 

2.  Dilute  sulphuric  acid  or  a  solution  of  a  sulphate  gives  a  white 
precipitate  of  lead  sulphate,  PbSO4.    This  is  one  of  the  four  insoluble 
sulphates.     (See  test  2  for  sulphates.) 

3.  Other  reagents  which  give  precipitates  with  solutions  of  lead 
salts  are : 

Hydrochloric  acid  or  solution  of  a  chloride,  producing  white  lead 
chloride,  PbCl2.  (See  test  3  for  hydrochloric  acid.) 

Potassium  iodide,  producing  yellow  lead  iodide,  PbI2  (Plate  III., 
6).  (See  test  2  for  iodides.) 

Potassium  chromate,  producing  yellow  lead  chromate  (chrome-yel- 
low), PbCr04  (Plate  II.,  6).  (See  test  2  for  chromates.) 

Alkali  carbonates,  producing  white  basic  lead  carbonate. 

Alkali  phosphates,  producing  white  lead  phosphate,  PbHPO4. 

Solution  of  sodium  hydroxide,  producing  white  lead  hydroxide, 
Pb(OH)2,  which  dissolves  in  excess  of  the  alkali,  forming  sodium 
plumbite,  Pb(ONa)2.  (See  comments  on  tests  for  zinc,  page  317.) 


LEAD — COPPER — BISMUTH.  323 

C  When  a  charcoal  reduction  test  (for  which  see  directions  in  test 
3  for  sulphates)  is  made  on  any  dry  lead  compound,  a  globule  of 
metallic  lead  is  obtained,  which  is  recognized  by  its  softness  and 
malleability.  Try  its  solubility  in  dilute  hydrochloric,  sulphuric,  and 
nitric  acids. 

Tests  1,  2,  and  4  are  sufficient  for  recognition  of  a  lead  compound. 
Lead  salts  are  mostly  colorless.  Lead  nitrate  has  an  acid  reaction, 
due  to  hydrolysis  in  water. 

Copper,  Cuu  =  63.1  (Cuprum).  Found  in  nature  sometimes  in  the 
metallic  state — generally,  however,  combined  with  sulphur  or  oxygen. 
The  commonest  copper-ore  is  Copper  pyrites,  a  double  sulphide  of 
copper  and  iron,  CuFeS2  or  Cu2S.Fe2S3,  having  the  color  and  lustre 
of  brass  or  gold.  Other  ores  are :  Copper  glance,  cuprous  sulphide, 
having  a  dark-gray  color  and  the  composition  Cu2S ;  malachite,  a 
beautiful  green  mineral,  being  a  carbonate  and  hydroxide  of  copper, 
CuCO3.Cu(OH)2.  Cuprous  and  cupric  oxide  also  are  found  occasion- 
ally. Copper  is  obtained  from  the  oxide  by  reducing  it  with  coke ; 
sulphides  previously  are  converted  into  oxide  by  roasting. 

Copper  is  the  only  metal  showing  a  distinct  red  color ;  it  is  so 
malleable  that,  of  the  metals  in  common  use,  only  gold  and  silver 
surpass  it  in  that  respect ;  it  is  one  of  the  best  conductors  of  heat  and 
electricity,  it  does  not  change  in  dry  air,  but  becomes  covered  with  a 
film  of  green  subcarbonate  when  exposed  to  moist  air. 

Copper  frequently  is  used  in  the  manufacture  of  alloys,  of  which 
the  more  important  are  : 

Copper.  Zinc.  Tin.  Nickel.       Antimony. 

Brass        ....  64  36 

German  silver  ...  51  31  ...  18 

Bell-metal         ...  78  ...  22 

Bronze      ....  80  16  4 

Gun-metal         ...  90  ...  10 

Babbit-metal     ...  43  ...  43  ...  14 

Copper  frequently  is  alloyed  with  gold  and  silver. 

Copper  forms  two  oxides,  and  corresponding  to  these  are  two  series 
of  salts,  known  as  cuprous  and  cupr/c  compounds.  Cuprous  salts  of 
oxygen  acids  do  not  exist.  The  principal  cuprous  compounds  are 
Cu2O,  CuCl,  CuBr,  Cul,  Cu(CN),  Cu2S.  All  these,  except  Cu2Oand 
Cu2S,  are  white  and  insoluble  in  water.  Cupric  iodide,  (CuI2),  and 
cyanide,  (Cu(CN)2),  cannot  be  obtained,  as  they  decompose  into  the 
cuprous  salt  and  free  iodine  or  cyanogen,  CuI2  =  Cul  +  I.  These  are 
obtained  when  potassium  iodide  or  cyanide  solution  is  added  to  solu- 
tion of  cupric  sulphate  : 

CuS04    -f     2KI    =    Cul    +     I    +    K2SO4, 


324  METALS  AND   THEIR   COMBINATIONS. 

Cupric  compounds  are  more  numerous,  as  they  embrace  the  salts  of 
oxygen  acids  as  well  as  salts  of  some  of  the  halogen  acids.  The 
anhydrous  salts  are  usually  white  or  yellow,  but  the  solutions  as  well  as 
the  hydrated  crystals  are  usually  blue  or  greenish  blue.  The  cupric 
compounds  are  more  important  and  familiar  than  the  cuprous  salts, 
and  those  most  frequently  employed  are  the  sulphate,  acetate,  and 
oxide.  The  valence  of  copper  in  cupric  compounds  is  2.  Some  facts 
indicate  that  in  the  cuprous  compounds  the  valence  of  copper  is  1, 
while  others  indicate  that  it  is  2.  Some  writers  assign  the  valence  of 
2  to  copper  in  all  its  compounds,  and  use  double  formulas  for  the 
cuprous  salts  to  account  for  the  apparent  univalence  of  copper,  thus, 
Cu2Cl2  or  Cl-Cu — Cu-Cl,  assuming  that  two  atoms  of  copper  are 
united  by  one  bond.  The  behavior  of  the  cuprous  salts  can  very 
readily  be  represented  by  the  simple  formulas  and  univalence  of  copper, 
and  there  is  no  need  for  using  double  formulas. 

Cupric  oxide,  CuO  (Black  oxide  or  monoxide  of  copper).  Heated 
to  redness,  copper  becomes  covered  with  a  black  scale,  which  is  cupric 
oxide ;  it  is  obtained  also  by  heating  cupric  nitrate  or  carbonate,  both 
compounds  being  decomposed  with  formation  of  the  oxide ;  finally, 
it  may  be  made  by  adding  sodium  or  potassium  hydroxide  to  the 
solution  of  a  cupric  salt,  when  a  bulky,  pale-blue  precipitate  of  cupric 
hydroxide,  Cu(OH)2,  is  formed,  which,  upon  boiling,  is  decomposed  into 
water  and  cupric  oxide,  a  heavy  dark-brown  powder  (Plate  III.,  2) : 

CuS04  +  2KOH  =  K2SO4  +  Cu(OH)2; 
Cu(OH)2  =  H2O     +  CuO. 

Cuprous  oxide,  Cu2O  ( Red  oxide  or  suboxide  of  copper).  When 
cupric  oxide  is  heated  with  metallic  copper,  charcoal,  or  organic 
matter,  the  cupric  oxide  is  decomposed,  and  cuprous  oxide  is  formed. 
(Excess  of  carbon  or  organic  matter  reduces  the  oxide  to  metallic 
copper.) 

CuO  -f  Cu  =  Cu2O; 
2CuO  +  C    =  Cu2O  +  CO. 

Some  organic  substances,  especially  grape-sugar,  decomposes  alkaline 
solutions  of  cupric  sulphate  with  precipitation  of  cuprous  oxide,  which 
is  a  red,  insoluble  powder. 

Experiment  40.  To  5  c.c.  of  a  5  per  cent,  solution  of  copper  sulphate  add 
about  20  c.c.  of  the  reagent  solution  of  sodium  hydroxide.  Note  the  blue  pre- 
cipitate of  copper  hydroxide,  Cu(OH)2.  Add  to  the  mixture  about  2  grammes 
of  Rochelle  salt  (sodium  potassium  tartrate)  and  shake.  The  precipitate  dis- 


LEA  D— COPPER—BISMUTH.  325 

solves  to  a  deep  blue  solution,  which  is  essentially  Fehling's  solution  (see  Index). 
The  copper  enters  the  negative  tartaric  acid  radical  or  ion,  and  while  in  the 
cupric  state  is  not  precipitated  by  alkali.  If  the  copper  is  reduced  to  the 
cuprous  state,  it  can  no  longer  remain  in  solution  and  is  precipitated  as  the 
reddish  cuprous  oxide,  Cu2O. 

Heat  the  blue  solution  to  boiling  and  add  a  little  dilute  glucose  solution  and 
heat  again  a  few  minutes.  A  precipitate  of  cuprous  oxide  is  produced,  due  to 
the  reducing  action  of  the  glucose.  This  is  usually  employed  as  a  test  for 
glucose  in  urine. 

Cupric  sulphate,  Cupri  sulphas,  CuSO4.5HO2  =  247.85  (Sul- 
phate of  copper,  Slue  vitriol,  Blue-stone).  This  is  the  most  important 
compound  of  copper.  It  is  manufactured  on  a  large  scale,  either 
from  copper  pyrites,  or  by  dissolving  cupric  oxide  in  sulphuric  acid, 
evaporating  and  crystallizing  the  solution. 

Cupric  sulphate  forms  large,  transparent,  deep-blue  crystals,  which 
are  easily  soluble  in  water,  and  have  a  nauseous,  metallic  taste.  By 
heating  it  to  about  200°  C.  (392°  F.)  all  water  of  crystallization  is 
expelled,  and  the  anhydrous  cupric  sulphate  formed,  which  is  a  white 
powder.  By  further  heating  this  is  decomposed,  sulphuric  and 
sulphurous  oxides  are  evolved,  and  cupric  oxide  is  left. 

Experiment  41.  Boil  about  5  grammes  of  fine  copper  wire  with  15  c.c.  of 
concentrated  sulphuric  acid  until  the  action  ceases  and  most  of  the  copper 
is  dissolved.  Dilute  with  about  15  c.c.  of  hot  water,  filter,  and  set  aside  for 
crystallization  State  the  exact  quantities  of  copper  and  H2S04  required  to 
make  100  pounds  of  crystallized  cupric  sulphate. 

Cupric  carbonate  is  obtained  by  the  addition  of  sodium  carbonate 
to  solution  of  cupric  sulphate,  when  a  bluish-green  precipitate  is 
formed,  which  is  cupric  carbonate  with  hydroxide  (Plate  III.,  4);  by 
dissolving  this  in  the  various  acids,  the  different  cupric  salts  are 
obtained. 

Ammoniocopper  compounds.  A  number  of  compounds  are 
known  which  are  either  double  salts  of  ammonia  and  copper,  or  are 
derived  from  ammonium  salts  and  contain  copper.  Thus,  cupric 
chloride  forms  with  ammonia  the  compounds :  CuCl2(NH3)2,  CuCl2 
(NH3)4,  and  CuCl2(NH3)6.  Cupric  sulphate  forms  in  like  manner, 
cupric- diammonium  sulphate,  CuSO4(NH3)2,  and  cupric  tetrammo- 
nium  sulphate,  CuSO4(NH3)4,  which  is  a  deep  azure-blue  compound 
taking  up  one  molecule  of  water  during  crystallization. 

It  is  this  formation  of  soluble  ammonio-copper  compounds  which 
causes  the  deep  blue  color  in  solutions  of  cupric  salts  on  the  addition 
of  ammonia  water. 


326  METALS  AND  THEIR  COMBINATIONS. 

All  copper  salts,  except  the  sulphide,  are  soluble  in  ammonia  water.  Hence, 
copper  cannot  be  precipitated  from  ammoniacal  solution  by  any  reagent  except 
hydrogen  sulphide  or  alkali  sulphides.  Copper  hydroxide  with  excess  of  am- 
monia water  forms  the  deep-blue  soluble  compound,  Cu(NH3)4.(OH)2,  in  which 
the  copper  is  held  in  the  complex  radical  or  ion,  Cu(NH3)4".  The  ammonio- 
copper  salts  are  derived  from  the  hydroxide  above,  and  also  contain  the  radical 
Cu(NH3)4",  which  is  the  cause  of  the  blue  color.  The  sulphate  has  the  for- 
mula Cu(NH3)4.SO4.H2O. 

With  excess  of  alkali  cyanides,  copper  also  forms  complex  double  cyanides, 
from  which  copper  cannot  be  precipitated  by  any  reagent,  not  even  hydrogen 
sulphide. 

Poisonous  properties  and  antidotes.  The  use  of  copper  for  culinary  vessels 
Is  frequently  the  cause  of  poisoning  by  this  metal.  A  perfectly  clean  surface  of 
metallic  copper  is  not  affected  by  any  of  the  substances  used  in  the  preparation 
of  food,  but  as  the  metal  is  very  apt  to  become  covered  with  a  film  of  oxide 
when  exposed  to  the  air,  and  as  the  oxide  is  easily  dissolved  by  the  combined 
action  of  water,  carbonic  or  other  .acids,  such  as  are  found  in  .vinegar,  the  juice 
of  fruits,  or  rancid  fats,  the  use  of  copper  for  culinary  vessels  is  always 
dangerous.  Actual  adulterations  of  food  with  compounds  of  copper  have  been 
detected. 

In  cases  of  poisoning  by  copper  the  stomach-pump  should  be  used,  vomiting 
induced,  and  albumen  (white  of  egg)  administered,  which  forms  an  insoluble 
compound  with  copper.  Reduced  iron,  or  a  very  dilute  solution  of  potassium 
ferrocyanide,  may  be  of  use  as  antidotes. 


Tests  for  copper. 
(Use  a  5  per  cent,  solution  of  copper  sulphate.) 

1.  Add  to  the  solution  hydrogen  sulphide  or  ammonium  sulphide : 
q,  black  precipitate  of  cupric  sulphide  is  formed.     (Plate  III.,  1)  : 

CuS04    +     H2S    ==     H2SO4    -f    CuS. 

2.  Add  solution  of  sodium  or  potassium  hydroxide  :  a  bluish  pre- 
cipitate of  cupric  hydroxide,  Cu(OH)2,  is  formed,  which  is  converted 
into   dark-brown    cupric  oxide,    CuO,    by  boiling.      (See   equation 
above.)     (Plate  III.,  2.) 

3.  Add  ammonia  water :  a  bluish  precipitate  of  cupric  hydroxide 
is  formed  which  readily  dissolves  in  an  excess  of  the  reagent,  forming 
a  deep  azure-blue  solution  containing  an  ammonio-copper  compound. 
(See  explanation  above.)     (Plate  III.,  3.) 

The  delicacy  of  this  test  is  shown  by  diluting  the  solution  of  the 
copper  salt  until  its  color  is  no  longer  visible,  and  then  adding 
ammonia. 


COPPER.    LEAD.    BISMUTH. 


PLATE 


Cupric    sulphide    or    lead    .sulphide, 

precipiiateil     from    Milutioiih    of    nipper    or 
lead  by   liydi ouen  sulphide. 


Cupric  hydroxide  passing  into  cupric 
oxide.  Cupric  solutions  precipitated  by 
potassium  hydroxide  and  boiling. 


Cupric    solutions    treated    with    am- 
monia water. 


Cupric  carbonate,  precipitated   from 

cupric  solutions  by  sodium  carbonate. 


Cupric  ferrocyanide,  precipitated 
from  cupric  solutions  by  potassium,  ferro- 
cyanide. 


Lead    iodide,    precipitated    from   lead 
solutions  by  soluble  iodides. 


Lead  solutions  with  soluble  chlorides, 
sulphates  or  carbonates.  Bismuth  solu- 
tions with  alkali  hydroxides  or  carbonates. 


Bismuth  sulphide,  precipitated    from 
bismuth  solutions  by  hydrogen  sulphide. 


,  Litti  Balliinocr.  .  Ifd 


LEA  D —  COPPER — BISM  mi.  327 

4.  Add  solution  of  potassium  ferrocyanide :  a  reddish-brown  pre- 
cipitate of  cupric  ferrocyanide,  Cu2Fe(CN)6,  is  obtained.  (Plate  III.,  5.) 

This  is  a  very  delicate  test,  and  should  also  be  made  on  a  highly 
diluted  solution  made  as  directed  in  test  3. 

5.  Add  solution  of   sodium  or  potassium  carbonate :  green  cupric 
carbonate  with  hydroxide  is  precipitated.     (Plate  III.,  4.) 

6.  Immerse  a  piece  of  iron  or  zinc,  showing  a  bright  surface,  in  an 
acidified  solution  of  copper :  the  latter  is  precipitated  upon  the  iron,  an 
equivalent  amount  of  iron  passing  into  solution.     (See  page  319.) 

CuS04    +    Fe  FeS04    +    Cu. 

7.  Most  compounds  of  copper  color  the  flame  green,  cupric  chloride, 
blue.     The  cupric  chloride  flame  can  be  made  very  striking  by  dis- 
solving  the  copper  salt  in  a  little    concentrated   hydrochloric  acid, 
pouring  this  solution  on  the  corner  of  a  piece  of  iron  wire  gauze,  and 
holding  it  in  the  Bunsen  flame. 

8.  Cupric  compounds  give  a  blue,  cuprous  compounds  a  red,  borax 
bead. 

Tests  3,  4,  6,  and  8  are  sufficient  to  identify  copper  compounds.  The 
insoluble  ones  are  made  soluble  by  treating  with  mineral  acids.  The 
sulphate,  nitrate,  chloride,  acetate,  and  ammonio-salts  of  copper  are 
soluble  in  water,  most  of  the  other  compounds  are  insoluble.  The 
soluble  normal  salts  redden  litmus,  due  to  hydrolysis. 

The  ionic  equations  for  the  tests  are  of  the  same  form  as  those  given  under 
the  tests  for  calcium. 

Bismuth,  Biiu  =  206.9.  Found  in  nature  chiefly  in  the  metallic 
state,  disseminated,  in  veins,  through  various  rocks.  The  extraction 
of  the  metal  is  a  mere  mechanical  process,  the  earthy  matter  contain- 
ing it  being  heated  in  iron  cylinders,  and  the  melted  bismuth  collected 
in  suitable  receivers. 

Bismuth  is  grayish-white,  with  a  pinkish  tinge,  very  brittle,  gen- 
erally showing  a  distinct  crystalline  structure.  Occasionally  it  is 
used  in  alloys  and  in  the  manufacture  of  a  few  medicinal  prepara- 
tions. 

Bismuth  has  the  property  of  expanding  while  passing  from  the  liquid  to  the 
solid  state,  and  of  greatly  lowering  the  fusing  point  of  other  metals.  These 
properties  make  it  a  useful  constituent  of  many  alloys.  The  presence  of  bis- 
muth in  dental  amalgams  renders  them  sticky  and  adhesive  and  causes  them 
to  require  a  larger  proportion  of  mercury. 

Bismuth  is  trivalent,  as  a  rule,  as  shown  in  the  chloride,  BiCl3,  or 
oxide,  Bi2O3,  but  it  is  also  quinquivalent,  as  shown  by  the  oxide, 


328  METALS  AND   THEIR   COMBINATIONS. 

Bi2O5,  corresponding  to  P2O5,  Sb2O5,  I2O5,  or  N2O5.  In  fact,  bismuth 
forms,  besides  the  two  oxides  mentioned,  two  others  of  the  composition 
Bi2O2  and  Bi2O4,  corresponding  to  the  respective  nitrogen  oxides. 
A  characteristic  property  of  this  metal  is  decomposition  of  the  con- 
centrated solution  of  any  of  its  normal  salts  by  the  addition  of  much 
water,  with  the  formation  and  precipitation  of  so-called  oxysalts  or 
subsalts  of  bismuth,  while  some  bismuth  with  a  large  quantity  of 
acid  remains  in  solution.  This  is  due  to  the  very  weak  basic  charac- 
ter of  Bi(OH)3. 

The  true  constitution  of  these  subsalts  is  as  yet  doubtful,  but  a 
comparison  of  them  has  led  to  the  assumption  of  a  radical  Bismuthyl, 
BiO,  which  behaves  like  an  atom  of  a  univalent  metal. 

The  relation  between  the  normal  or  bismuth  salts,  and  the  subsalts 
or  bismuthyl  salts,  will  be  shown  by  the  composition  of  the  following 
compounds : 

Bismuth  chloride,  BiCl3.  Bismuth yl  chloride,  (BiO)CL 

"        bromide,  BiBr3.  "          bromide,  (BiO)Br. 

iodide,  BiI3.  •'          iodide,  (BiO)I. 

"        nitrate,  Bi(NO3)3.  "          nitrate,  (BiO)NO3. 

sulphate,  Bi2(S04)3.  "          sulphate,  (BiO)2SO4. 

«        carbonate,  Bi2(CO3)3  j  „          carbonate,  (BiO)2CO3. 

not  known. ) 

The  nature  of  normal  bismuth  salts  and  bismuthyl  salts  may  be 
explained  by  saying  that  the  first  are  derived  from  the  triacid  base 
Bi(OH)3,  the  latter  from  the  monacid  base  BiO.OH.  These  two 
hydroxides  are  related  to  one  another  thus  : 

Bi(OH)3  =  Bi/°H  +  H20. 

Bismuth  subnitrate,  Bismuthi  subnitras,  BiONO3.H2O  ?  (Oxy- 
nitrate  of  bismuth}.     By  dissolving  metallic  bismuth  in  nitric  acid,  a 
solution  of  bismuth  nitrate  is  obtained,  nitrogen  dioxide  escaping : 
Bi  +  4HNO3  =  Bi(NO3)3  +  NO  +  2H2O. 

Upon  evaporation  of  the  solution,  colorless  crystals  of  bismuth 
nitrate,  Bi(NO3)35H2O,  are  obtained. 

If,  however,  the  solution  (or  the  dissolved  crystals)  be  poured  into 
a  large  quantity  of  water,  the  salt  is  decomposed  with  the  formation 
of  bismuthyl  nitrate  and  nitric  acid,  which  latter  keeps  in  solution 
some  bismuth  : 

Bi(N(V3  +  2H20  =  BiON03.H2O  +  2HNO3 

Subnitrate  of  bismuth   is  a  heavy,  white,  tasteless  powder,  of  a 


LEAD-  COPPER— BISMUTH.  329 

somewhat  varying  chemical  composition  ;   it  is   almost  insoluble  in 
water,  soluble  in  most  acids. 

Experiment  42.  Dissolve  by  the  aid  of  heat  about  1  gramme  of  metallic  bis- 
muth in  a  mixture  of  2  c.c.  of  nitric  acid  and  1  c.c.  of  water.  Evaporate  the 
clear  solution  to  about  one-half  its  volume,  in  order  to  remove  excess  of  acid, 
and  pour  this  solution  of  normal  bismuth  nitrate  into  100  c.c.  of  water.  Col- 
lect the  precipitate  of  bismuthyl  nitrate  on  a  filter,  wash  and  dry  it.  Prove 
the  presence  of  bismuth  in  the  filtrate  by  tests  mentioned  below. 

Bismuth  subcarbonate,  Bismuth!  subcarbonas  (BiO)2CO3. 
H2O  (?)  (Oxy  carbonate  of  bismuth,  Pearl-white).  Made  by  adding 
sodium  carbonate  to  solution  of  bismuth  nitrate,  when  the  subcarbo- 
nate is  precipitated,  some  carbon  dioxide  escaping : 

2Bi(N03)s  +  3Na2CO3  +  H2O  =  6NaNO3  -f  2CO2  +  (BiO)2CO3.H2O. 
A  white,  or  pale  yellowish-white  powder,  resembling  the  subnitrate. 
It  readily  loses  water  and  carbon  dioxide  on  heating,  when  the  yellow 
oxide,  Bi2O3,  is  left. 

A  mixture  of  bismuth  subnitrate,  sodium  bicarbonate,  and  water  is  often 
prescribed,  but,  as  such  a  mixture  gives  off  carbon  dioxide,  it  is  better  to  sub- 
stitute the  subcarbonate  for  the  subnitrate. 


Tests  for  Bismuth. 

Use  a  solution  made  by  dissolving  bismuth  subnitrate  or  subcar- 
bonate in  the  least  possible  quantity  of  dilute  nitric  acid,  with  gentle 
heat.  Dilute  cautiously  with  water,  adding  a  few  drops  more  of  the 
acid  if  there  is  any  tendency  to  precipitation. 

1.  Add  to  the  solution  hydrogen  sulphide  or  ammonium  sulphide : 
a  dark-brown  (almost  black)  precipitate  of  bismuth  sulphide,  Bi2S3, 
is  produced  (Plate  III.,  8) : 

2BiCl3    +    3H2S    =    6HC1    +    Bi2S3. 

2.  Add  solution  of  ammonium  or  sodium  hydroxide,  or  carbonate  : 
a  white  precipitate  of  bismuth  hydroxide,  Bi(OH)3,  or  of  bismuthyl 
carbonate  is  produced.     (See  explanation  above.) 

3.  Solution  of  potassium  iodide  precipitates  brown  bismuth  iodide, 
B5I3,  soluble  in  excess  of  the  reagent. 

4.  Solution  of  potassium  dichromate  precipitates  yellow  bismuthyl 
dichromate,  (BiO)2Cr2O7. 

5.  A  small  quantity  of  bismuth    or   of  any  bismuth  compound, 
mixed  with  equal  quantities  of  sulphur  and  potassium  iodide,  and 


330  METALS  AND  THEIR  COMBINATIONS. 

heated  moderately  upon  charcoal  before  the  blowpipe,  forms  a  scar- 
let-red incrustation  of  bismuthyl  iodide,  BiOI. 

6.  Apply  the  reduction  test  on  charcoal  (see  directions  in  test  3 
for  sulphuric  acid)  to  any  dry  bismuth  compound.  A  hard,  brittle  bead 
of  metallic  bismuth  is  produced,  which,  if  dissolved  in  a  little  con-, 
centrated  hydrochloric  acid,  aided  by  a  few  drops  of  nitric  acid,  and 
the  solution  then  be  strongly  diluted  with  water,  gives  a  dense  white 
precipitate  of  bismuth  subchloride, 

BiCL,    +     H20     =     BiOCl     +     2HC1. 

Tests  1,  5,  and  6  together  are  sufficient  to  identify  a  bismuth  com- 
pound. The  insoluble  or  sub-salts  are  the  most  stable,  and  can  be  dis- 
solved by  acids,  forming  the  normal  salts.  The  latter  cannot  exist 
in  aqueous  solution,  except  in  the  presence  of  an  acid.  The  decomposi- 
tion of  normal  salts  of  bismuth  by  water  into  insoluble  sub-salts  is  the 
most  characteristic  property  of  bismuth.  One  other  metal  resembles 
it  in  this  respect,  namely,  antimony,  but  its  sulphide  has  an  orange 
color. 

The  most  readily  obtained  sub-salt  of  bismuth  is  the  subchloride, 
BiOCl .  If  no  precipitate  occurs  when  diluting  the  nitrate  solution 
(because  of  too  much  acidity),  addition  of  solution  of  ammonium  or 
sodium  chloride  produces  a  precipitate  of  the  subchloride  imme- 
diately. 

31.    SILVER— MERCURY. 

Silver,  Ag  =  107.12  (Argentum).  This  metal  is  found  sometimes 
in  the  metallic  state,  but  generally  as  a  sulphide,  which  is  nearly 
always  in  combination  with  large  quantities  of  lead  sulphide,  such 
ore  being  known  as  argentiferous  galena.  The  lead  manufactured 
from  this  ore  contains  the  silver,  and  is  separated  from  it  by  roasting 
the  alloy  in  a  current  of  air,  whereby  lead  is  oxidized  and  converted 
into  litharge,  while  pure  silver  is  left. 

QUESTIONS. — What  are  the  properties  of  lead,  and  from  what  ore  is  it  ob- 
tained? What  is  litharge,  and  how  does  it  differ  from  red  lead?  Give  the 
composition  of  nitrate,  carbonate,  and  iodide  of  lead;  how  are  they  made? 
State  the  analytical  reactions  for  lead.  How  is  copper  found  in  nature  ?  How 
many  oxides  of  copper  are  known  ;  what  is  their  composition,  and  under  what 
conditions  are  they  formed?  What  is  "blue  vitriol";  how  is  it  made,  and 
what  are  its  properties?  How  does  ammonium  hydroxide  act  on  cupric  solu- 
tions? Mention  tests  for  copper.  What  is  the  composition  of  subnitrate  and 
subcarbonate  of  bismuth  ;  how  are  they  made  from  metallic  bismuth,  and  what 
explanation  is  given  in  regard  to  their  constitution  ? 


SILVER— MERCURY.  331 

Silver  is 'the  whitest  of  all  metals,  and  takes  the  highest  polish  ; 
it  is  the  best  conductor  of  heat  and  electricity,  and  melts  at  about 
1000°  C.  (1832°  F.);  it  is  univalent,  and  forms  but  one  series  of  salts; 
it  is  not  affected  by  the  oxygen  of  the  air  at  any  temperature,  but  is 
readily  acted  upon  by  traces  of  hydrogen  sulphide,  which  forms  a 
black  film  of  sulphide  upon  the  surface  of  metallic  silver.  Hydro- 
chloric acid  scarcely  acts  on  silver,  nitric  and  sulphuric  acids  dis- 
solve it. 

While  many  of  the  non-metallic  elements  have  long  been  known  to  exist  in 
allotropic  forms,  none  of  the  metals  had  been  obtained  in  such  a  condition 
until  quite  recently,  when  it  was  shown  that  silver  is  capable  of  assuming  a 
number  of  allotropic  modifications.  These  are  obtained  chiefly  by  precipi- 
tating silver  from  solutions  by  different  reducing  agents.  While  normal  silver 
is  white,  the  allotropic  forms  have  distinct  colors  —blue,  bluish-green,  red,  pur- 
ple, yellow — and  differ  also  in  many  other  respects.  Thus  they  are  converted 
into  silver  chloride  by  highly  diluted  hydrochloric  acid,  which  does  not  act 
on  common  silver;  they  are  soluble  in  ammonia  water,  and  act  as  reducing 
agents  upon  a  number  of  substances,  such  as  permanganates,  ferricyanides, 
etc.  Allotropic  silver  can  be  converted  into  the  common  form  by  dift 
ferent  forms  of  energy — for  instance,  by  heat,  electricity,  and  the  action  of 
strong  acids. 

This  allotropic  form  of  silver  is  known  as  colloidal  silver,  and  its  solution  in 
water  is  not  a  true,  but  a  colloidal  solution.  Such  a  solution  has  the  same  freez- 
ing- and  boiling-point  as  water  itself,  and  it  has  been  shown  that  the  colloid  is 
simply  suspended  in  the  liquid,  although  it  is  in  too  fine  a  state  of  division  to 
be  retained  by  a  filter-paper.  Colloidal  solutions  of  silver,  gold,  or  platinum 
result  when  electric  discharges  pass  between  wires  of  these  metals  held  under 
water. 

Collargol  (Argentum  Crede)  is  a  preparation  of  colloidal  (soluble) 
silver,  said  to  contain  85.87  per  cent,  of  silver  and  a  small  amount  of  albumin. 
It  is  bluish-black,  scale-like,  soluble  in  20  parts  of  water.  Albumin  is  added 
to  prevent  precipitation  of  silver  from  its  solution  by  acids  and  salts,  or  by 
heating.  It  is  incompatible  with  the  usual  silver  reagents. 

Collargol  Ointment  (Unguentum  Crede")  is  an  ointment  containing  15  per 
cent,  of  collargol,  of  a  dark,  bluish-gray  color. 

Silver  is  too  soft  for  use  as  coin  or  silverware,  and,  therefore,  is 
alloyed  with  from  5  to  25  per  cent,  of  copper,  which  causes  it  to  be- 
come harder,  and  consequently  gives  it  more  resistance  to  the  wear 
and  tear  by  friction. 

Pure  silver  may  be  obtained  by  dissolving  silver  coin  in  nitric  acid, 
when  a  blue  solution,  containing  the  nitrates  of  copper  and  silver,  is 
formed.  By  the  addition  of  sodium  chloride  to  the  solution  a  white 
curdy  precipitate  of  silver  chloride,  AgCl,  forms,  while  cupric  nitrate 


332  METALS  AND   THETR   COMBINATIONS. 

remains  in  solution.  The  silver  chloride  is  washed,  dried,  mixed 
with  sodium  carbonate,  and  heated  in  a  crucible,  when  sodium  chlo- 
ride is  formed,  carbon  dioxide  escapes,  and  a  button  of  silver  is  found 
at  the  bottom  of  the  crucible : 

2AgCl  +  Na2C03  =  2NaCl  +  CO2  +  2Ag  +  O. 

Experiment  43.  Dissolve  a  small  silver  coin  in  nitric  acid,  dilute  with  water, 
and  precipitate  the  clear  liquid  with  an  excess  of  solution  of  sodium  chloride. 
The  washed  precipitate  of  silver  chloride  may  be  treated  with  sodium  carbon- 
ate, as  stated  above,  or  may  be  converted  into  metallic  silver  by  the  following 
method :  Place  the  dry  chloride  in  a  small  porcelain  crucible  and  apply  a 
gentle  heat  until  the  chloride  has  fused ;  when  cold,  place  a  piece  of  sheet 
zinc  upon  the  chloride,  cover  with  water,  to  which  a  few  drops  of  sulphuric 
acid  have  been  added,  and  set  aside  for  a  day,  when  the  silver  chloride  will  be 
found  to  have  been  decomposed  with  liberation  of  metallic  silver  and  forma- 
tion of  zinc  chloride. 

A  simpler  method  is  to  heat  the  silver  chloride  with  a  solution  of  formal- 
dehyde and  a  few  drops  of  alkali,  or  with  glucose  and  alkali.  Metallic  silver 
in  a  finely  divided  state  is  obtained,  which,  after  washing,  may  be  fused  into 
a  lump. 

Silver  nitrate,  Arg-enti  nitras,  AgNO3  =  168.69.  Pure  silver  is 
dissolved  in  nitric  acid  : 

3Ag  +  4HN03  =  NO  +  2H2O  +  3AgNO3. 

The  solution  is  evaporated  to  dryness  with  the  view  of  expelling  all 
free  acid,  the  dry  mass  dissolved  in  hot  water  and  crystallized. 

If  the  silver  used  should  contain  copper,  the  latter  may  be  elimin- 
ated from  the  mixture  of  silver  and  cupric  nitrate  by  evaporating  to 
dryness  and  fusing,  when  the  latter  salt  is  decomposed,  insoluble 
cupric  oxide  being  formed.  The  fused  mass  is  dissolved  in  water, 
filtered,  and  again  evaporated  for  crystallization. 

When  silver  nitrate,  after  the  addition  of  4  per  cent,  of  hydro- 
chloric acid,  is  fused  and  poured  into  suitable  moulds  it  yields  the 
white  cylindrical  sticks  which  are  known  as  moulded  silver  nitrate, 
caustic,  lunar  caustic,  or  lapis  infernalis. 

When  fused  with  twice  its  weight  of  potassium  nitrate  and  formed 
into  similar  rods,  it  forms  the  mitigated  or  diluted  silver  nitrate  (mit- 
igated caustic)  of  the  U.  S.  P. 

Silver  nitrate  forms  colorless,  transparent,  tabular,  rhombic  crys- 
tals, or,  when  fused,  a  white,  hard  substance;  it  is  soluble  in  less 
than  its  own  weight  of  water,  the  solution  having  a  neutral  reaction. 
Exposed  to  the  light,  especially  in  the  presence  of  organic  matter, 
silver  nitrate  blackens  in  consequence  of  decomposition ;  when 


8IL  VER—MERCUR  Y.  333 

brought  in  contact  with  animal  matter,  it  is  readily  decomposed  into 
free  nitric  acid  and  metallic  silver,  which  produces  the  characteristic 
black  stain ;  it  is  this  decomposition,  and  the  action  of  the  free  nitric 
acid,  to  which  the  strongly  caustic  properties  of  silver  nitrate  are 
due. 

Silver  nitrate  is  used  for  various  kinds  of  indelible  inks  and  hair- 
dyes,  and  very  largely  in  the  manufacture  of  those  silver  compounds 
employed  for  photographic  purposes. 

Photography  is  the  art  of  obtaining  images  of  objects  by  means 
of  chemical  changes  produced  in  certain  substances  (chiefly  com- 
pounds of  silver  or  platinum)  by  the  action  of  light.  Three  separate 
operations  are  required  to  obtain  the  image ;  they  are  exposure,  devel- 
oping and  fixation. 

The  exposure  of  a  light-sensitive  surface  to  a  projected  image  of  the  object  to 
be  photographed  is  made  in  the  camera,  which  is  so  arranged  that  the  image 
can  be  thrown  upon  the  surface  by  means  of  a  lens.  The  surface  used  is  gen- 
erally that  of  a  glass  plate  or  a  gelatine  film,  sensitized  with  the  bromide  or 
iodide  of  silver. 

On  the  exposed  plate  a  chemical  change  has  taken  place  in  the  silver  salt 
wherever  light  has  acted  on  it.  The  exact  nature  of  this  change  is  not  under- 
stood, and  nothing  can  be  detected  on  the  plate  with  the  eye  after  exposure. 
But  when  the  exposed  plate  is  treated  with  certain  solutions,  called  developers, 
that  portion  of  the  silver  salt  which  has  been  acted  upon  by  light  is  decomposed 
with  the  formation  of  a  deposit  of  metallic  silver,  forming  the  visible  image. 
The  acting  constituent  of  developers  are  deoxidizing  agents,  such  as  pyrogallol, 
hydroquinone,  ferrous  sulphate,  etc. 

After  the  silver  image  has  appeared  there  yet  remains  on  the  plate  that  por- 
tion of  the  silver  salt  which  has  not  been  acted  on  by  light,  and  consequently 
not  by  the  developer.  This  portion  of  the  undecomposed  silver  salt  must  be 
removed  before  the  plate  can  be  taken  to  the  light,  and  this  removal,  called 
fixation,  is  accomplished  by  immersion  of  the  plate  in  a  fixing  solution  of 
sodium  thiosulphate,  Na2S203  (hyposulphite),  which  dissolves  the  salt  in  con- 
sequence of  the  formation  of  a  double  salt  of  the  composition  Ag2S203. 2Na2S203 ; 
this  is  eliminated  by  washing  in  water. 

The  image  thus  obtained  is  called  a  negative,  because  it  shows  dark  what 
ought  to  be  light,  and  vice  versa.  By  placing  this  negative  upon  sensitized 
material  (generally  paper)  and  permitting  light  to  pass  through  the  negative 
to  the  underlying  paper  the  light-sensitive  material  is  chemically  affected  most 
where  the  silver  deposit  in  the  negative  is  the  thinnest,  and  vice  versa.  By 
developing  and  fixing  the  exposed  paper  the  positive  picture  is  obtained. 

Silver  oxide,  Arg-enti  oxidum,  Ag2O  =  23O.12.  Made  by  the 
addition  of  an  alkali  hydroxide  to  silver  nitrate : 

2AgN03  +  2KOH  =  2KNO3  +  H2O  +  Ag2O 


334  METALS  AND  THEIR   COMBINATIONS. 

A  dark-brown,  almost,  black  powder,  but  very  sparingly  soluble 
in  water,  imparting  to  the  solution  a  weak  alkaline  reaction.  It  is  a 
strong  base,  and  easily  decomposed  into  silver  and  oxygen. 

Antidotes.    Sodium  chloride,  white  of  egg,  or  milk,  followed  by  an  emetic. 

Complex  silver  compounds.  A  great  many  combinations  of  silver 
with  organic  substances  have  been  introduced  and  a  few  are  extensively  em- 
ployed in  medicine.  These  compounds  usually  differ  in  properties  from  the 
inorganic  salts  of  silver.  They  are  antiseptic  and  less  irritating  than  silver 
nitrate. 

Argonin,  silver-casein,  is  a  soluble  casein  compound  containing  4.28  per  cent. 
of  silver.  It  is  a  nearly  white  powder,  soluble  in  water,  from  which  the  silver 
is  not  precipitated  by  sodium  chloride  or  hydrogen  sulphide.  It  is  also  soluble 
in  alkalies,  egg-albumin,  blood-serum,  etc. 

Argyrol,  silver  vitellin,  is  a  compound  of  a  derived  proteid  and  silver  oxide, 
containing  from  20  to  25  per  cent,  of  silver.  It  occurs  as  black,  glistening 
hygroscopic  scales,  freely  soluble  in  water  and  glycerin,  insoluble  in  oils  and 
alcohol.  It  is  said  to  be  incompatible  with  acids  and  most  of  the  neutral  and 
acid  salts  in  strong  solution. 

Protargol  is  a  compound  of  albumin  and  silver,  containing  8.3  per  cent,  of 
silver.  It  is  a  yellow  powder,  soluble  in  2  parts  of  cold  water.  The  silver  is 
not  precipitated  by  the  usual  reagents,  such  as  alkalies,  sulphides,  chlorides, 
bromides,  iodides,  nor  by  heat.  It  is  compatible  with  picric  acid  and  its  salts 
and  with  most  metallic  salts,  but  is  precipitated  by  cocaine  hydrochloride, 
which,  however,  may  be  prevented  by  addition  of  boric  acid.  It  is  a  non-irri- 
tant bactericide  and  antiseptic,  extensively  used  as  a  substitute  for  silver 
nitrate. 

Tests  for  Silver. 
(Use  a  1  per  cent,  solution  of  silver  nitrate  in  distilled  water.) 

1.  Add  to  the  solution  hydrogen  sulphide  or  ammonium  sulphide  : 
a  dark-brown  precipitate  of  silver  sulphide  is  produced  : 


2AgNO,    +    HaS    =    2HNO3    +    Ag2S. 

2.  Add  hydrochloric  acid,  or  solution  of  any  soluble  chloride  :  a 
white,  curdy  precipitate  of  silver  chloride  is  produced,  which  is  in- 
soluble in  dilute  acids,  but  soluble  in  ammonium  hydroxide  and  in 
potassium  cyanide  : 

AgN03    +    NaCl    =    NaN03    +    AgCl. 

3.  Add  potassium  chromate  or  dichromate  solution  :  a  red  precipi- 
tate of  silver  chromate,  Ag2CrO4,  is  formed  (Plate  II.,  7). 

4.  Add  sodium  phosphate  solution  :  a  pale-yellow  precipitate  of 
silver  phosphate,  Ag3PO4,  is   formed,  which  is  soluble  in  ammonia 
and  in  nitric  acid.     Free  phosphoric  acid  does  not  give  a  precipitate. 


SILVER— MERCURY.  335 

5.  Solution   of   alkali   hydroxides  precipitates  dark-brown  silver 
oxide,   soluble   in  ammonia   water,   forming  a  complex    hydroxide 
Ag(NH3)2.OH. 

6.  Solution  of   potassium  iodide  or  bromide  gives  a  pale-yellow 
precipitate. 

7.  Metallic  copper  or  zinc  precipitates  metallic  silver  from  solu- 
tions of  silver  in  any  form  of  combination.     (See  page  319.)      » 

Test  2  is  sufficient  to  identify  silver  in  ordinary  solutions,  for, 
although  mercurous  and  lead  chloride  are  insoluble  in  water  and 
dilute  acids,  silver  chloride  alone  of  these  three  insoluble  chlorides 
is  soluble  in  ammonia  water.  Silver  forms  a  number  of  complex 
combinations  with  organic  compounds  from  which  it  is  not  easily  pre- 
cipitated, but  by  reduction  of  the  silver  to  the  metallic  state,  and 
solution  of  the  metal  in  nitric  acid,  the  tests  may  be  applied.  The 
same  procedure  applies  also  to  inorganic  insoluble  silver  compounds, 
as  AgCl,  AgBr,  Agl,  Ag2S. 

All  silver  salts  are  soluble  in  ammonia  water,  except  the  iodide  and  sul- 
phide ;  hence  the  latter  alone  can  be  precipitated  from  an  ammoniacal  solution. 
In  these  solutions  complex  combinations,  as  Ag(NH3)2.NO3,  Ag(NH,)tCl,  are 
formed,  which  are  salts  of  the  hydroxide,  Ag(NH3)2.OH.  In  this  respect  silver 
acts  very  much  like  copper.  These  compounds  dissociate  thus: 

Ag(NH3)2N03  5±  Ag(NH3)2-  +  NO/. 

The  Ag(NH3)./  ions  yield  a  slight  amount  of  Ag*  ions,  but  not  enough  to  be 
precipitated  by  any  of  the  reagents  except  iodide  and  sulphide.  The  concen- 
tration of  Ag'  ions  given  by  the  latter  precipitates  is  less  than  that  given  by 
the  Ag(NH3)2*  ions,  hence  precipitation  takes  place.  (See  page  193.) 

Solutions  of  alkali  cyanides  and  thiosulphates  dissolve  all  silver  compounds, 
giving  complex  substances  of  the  form  KAg(CN)2  and  Na3Ag(S2O3)2.  The  ions 
of  these  are  K*  +  Ag(CN)/,  and  3Na*  -f  Ag(S2O3)///.  Such  a  slight  amount 
of  Ag*  ions  are  formed  from  these  compounds  that  no  reagent  will  give  a  pre- 
cipitate. That  there  are  some  Ag*  ions,  however,  is  shown  by  the  fact  that 
active  metals,  like  zinc,  separates  the  silver  from  the  solutions.  Also  that  in 
electroplating  silver  is  deposited  from  cyanide  solution. 

Soluble  silver  salts  are  not  hydrolyzed,  and  are,  therefore,  neutral. 

Mercury,  Hydrargyrum,  Hg  =  198.5  (Quicksilver).  Mercury  is 
found  sometimes  in  small  globules  in  the  metallic  state,  but  generally 
as  mercuric  sulphide  or  cinnabar,  a  dark-red  mineral.  The  chief 
supply  was  formerly  obtained  from  Spain  and  Austria ;  now,  how- 
ever, large  quantities  are  obtained  from  California ;  it  is  also 
imported  from  Peru  and  Japan. 

Mercury  is  obtained  from  cinnabar  either  by  roasting  it,  whereby 
the  sulphur  is  converted  into  sulphur  dioxide,  or  by  heating  it  with 
lime,  which  combines  with  the  sulphur,  while  the  metal  volatilizes, 
and  is  condensed  by  passing  the  vapors  through  suitable  coolers. 


336  METALS  AND   THEIR   COMBINATIONS. 

Mercury  is  the  only  metal  showing  the  liquid  state  at  the  ordinary 
temperature ;  it  solidifies  at  -40°  C.  (-40°  F.),  and  boils  at  357°  C. 
(675°  F.) ;  but  is  slightly  volatile  at  all  temperatures ;  it  is  almost 
silver-white,  and  has  a  bright  metallic  lustre ;  its  specific  gravity  is 
13.56  at  15°  C.  (59°  F.). 

Pure  mercury  should  present  a  bright  surface  even  after  agitation  with  air; 
when  dropped  on  paper  it  should  form  globules  which  roll  about  freely,  retain 
their  globular  form  and  leave  no  streaks.  Commercial  mercury  is  often  con- 
taminated with  tin,  lead,  bismuth  and  zinc.  Such  impurities  cause  a  trail  of 
dross  when  globules  are  made  to  roll  over  paper. 

Mercury  can  be  purified  by  repeated  distillation,  or  by  covering  the  metal 
with  nitric  acid  and  agitating  the  mass  frequently  during  two  days.  The  total 
of  the  base  metals,  with  some  mercury,  pass  in  solution,  which  is  washed  out  with 
water,  after  which  the  mercury  is  dried  by  setting  it  in  a  warm  place. 

Mercury  is  peculiar  in  that  its  molecule  contains  but  one  atom,  at 
least  when  in  the  state  of  a  gas ;  in  the  liquid  and  solid  states  it  may 
contain  two  atoms,  like  most  other  elements,  but  we  have  as  yet  no 
means  of  proving  this  fact. 

Mercury  forms,  like  copper,  two  series  of  compounds,  distinguished 
as  mercuric  and  mercurous  compounds.  In  the  former,  mercury  is 
bivalent,  while  in  mercurous  compounds  the  atom  exerts  a  valence  of 
one.  It  was  long  supposed  that  this  was  due  to  the  fact  that  two 
mercury  atoms  were  joined  together,  each  atom  thereby  losing  one 
of  its  points  of  affinity,  leaving  but  one  point  for  combining  Avith 
another  atom  or  radicle.  This  view  necessitated  the  existence  of  two 
mercury  atoms  in  the  molecule  of  every  mercurous  compound,  the 
composition,  for  instance,  of  mercurous  chloride  being  CIHg-HgCl  or 
Hg2Cl2.  There  are,  however,  good  reasons  to  believe  that  mercury  is 
univalent  in  mercurous  compounds,  the  composition  of  mercurous 
chloride  being,  consequently,  HgCL  Similarly,  copper  is  assumed  to 
be  univalent  in  cuprous  compounds. 

Mercury  is  not  affected  by  the  oxygen  of  the  air,  nor  by  hydro- 
chloric acid,  while  chlorine,  bromine,  and  iodine  combine  with  it 
directly,  and  warm  sulphuric  and  nitric  acids  dissolve  it. 

Mercury  is  used  in  the  metallic  state  for  many  scientific  instruments 
(thermometer,  barometer,  etc.);  for  making  amalgams;  for  extracting 
gold  from  the  ore  ;  for  manufacturing  from  it  all  of  the  various  mer- 
cury compounds,  and  those  official  preparations  in  which  mercury 
exists  in  the  metallic  state. 

These  latter  preparations  are  :  Mercury  with  chalky  mass  of  mercury, 
or  blue  pill,  mercurial  ointment,  and  mercurial  plaster.  Mercury  exists 
in  a  metallic,  but  highly  subdivided,  state  in  these  preparations,  which 
are  made  by  intimately  mixing  (triturating)  metallic  mercury  with 


SILVER— MERCURY.  337 

the  different  substances  used  (viz.,  chalk,  pill-mass,  fat,  lead -pi  aster). 
It  is  most  probable  that  the  action  of  these  agents  upon  the  animal 
system  is  chiefly  due  to  the  conversion  of  small  quantities  of  mercury 
into  mercurous  oxide,  which,  in  contact  with  the  acids  of  the  gastric 
juice  or  with  perspiration,  are  converted  into  soluble  compounds 
capable  of  being  absorbed. 

Amalgams.  Alloys  containing  mercury  are  termed  amalgams.  Mercury 
unites  with  most  metals,  and  with  some  of  them  it  forms  definite  compounds. 
Dental  alloys  used  for  amalgamation  are  composed  chiefly  of  silver  and  tin  with 
one  or  more  of  the  following  metals :  gold,  platinum,  copper,  zinc.  Dental 
amalgams  are  made  by  reducing  the  alloy  ingot  to  fine  shavings  or  filings, 
which  are  triturated  with  the  necessary  quantity  of  mercury  to  form  a  plastic 
mass,  which  becomes  hard  or  sets. 

The  properties  most  essential  for  a  good  amalgam  are  strength,  immutability 
as  to  volume,  freedom  from  discoloration,  and  resistance  to  the  action  of  the 
oral  secretions.  Many  formulas  have  been  suggested  to  obtain  these  results. 

The  addition  of  either  gold,  platinum,  copper  or  zinc  to  a  silver-tin  alloy 
facilitates  setting,  while  this  is  retarded  by  an  excess  of  mercury  or  by  the  em- 
ployment of  an  alloy  that  has  been  long  exposed  to  the  air  or  has  been  annealed. 
The  change  in  form — i.  e.,  expansion  or  contraction — which  an  amalgam  under- 
goes in  hardening  is  very  objectionable  and  difficult  to  completely  overcome. 

The  discoloration  of  amalgams  is  in  great  measure  due  to  the  formation  of 
sul  phides,  particularly  upon  those  amalgams  in  which  there  is  not  complete  chem- 
ical union  of  the  metallic  constituents.  A  proper  proportion  of  zinc  in  an  alloy 
prevents  discoloration  considerably,  making,  however,  the  alloy  difficult  to  amal- 
gamate, while  the  presence  of  copper  greatly  increases  the  tendency  to  discolor. 

Mercurous  oxide,  Hg^O  (Black  oxide  or  suboxide  of  mercury).  An 
almost  black,  insoluble  powder,  made  by  adding  an  alkaline  hydroxide 
to  a  solution  of  mercurous  nitrate  : 

2HgN03  +  2KOH  ==  2KNO3  +  H2O  -f  Hg.2O. 

A  similar  decomposition  takes  place  when  alkaline  hydroxides  are 
added  to  insoluble  mercurous  chloride.  A  mixture  of  lime-water  and 
mercurous  chloride  (calomel)  is  known  as  black-wash ;  when  the  two 
substances  are  mixed,  calomel  is  converted  into  mercurous  oxide,  while 
calcium  chloride  is  formed : 

2HgCl  +  Ca(OH)2  =  CaCl2  -f  H2O  +  Hg2O. 

Mercuric  oxide,  HgO  =  214.38.  There  are  two  mercuric  oxides 
which  are  official ;  they  do  not  differ  in  their  chemical  composition, 
but  in  their  molecular  structure. 

The  yellow  mercuric  oxide,  Hydrargyrioxidumflavum,  is  made  by  pour- 
ing a  solution  of  mercuric  chloride  into  a  solution  of  sodium  hydroxide, 
when  an  orange-yellow,  heavy  precipitate  is  produced,  which  is  washed 
and  dried  at  a  temperature  not  exceeding  30°  C.  (86°  F.)  (Plate  IV.,  3) : 
HgCl2  +  2NaOH  =  HgO  +  SNaCl  +  H2O. 

The  red  mercuric  oxide,  Hydrargyri  oxidum  rubrum,  is  made  by 

22 


338  METALS  AND  THEIR   COMBINATIONS. 

heating  mercuric  nitrate,  either  by  itself  or  after  it  has  been  intimately 
mixed  with  an  amount  of  metallic  mercury  equal  to  the  mercury  in 
the  nitrate  used  (Plate  IV.,  4).  In  the  first  case,  nitrous  fumes  and 
oxygen  are  given  off,  mercuric  oxide  remaining  : 

Hg(N03)2  =  HgO  +  2N02  -f  O. 
In  the  other  case,  no  oxygen  is  evolved : 

Hg(N08),  +  Hg  =  2HgO  +  2N02. 

The  red  oxide  of  mercury  differs  from  the  yellow  oxide  in  being 
more  compact,  and  of  a  crystalline  structure;  while  the  yellow  oxide 
is  in  a  more  finely  divided  state,  and  consequently  acts  more  energeti- 
cally when  used  in  medicine.  Yellow  oxide,  when  digested  on  a 
water-bath  with  a  strong  solution  of  oxalic  acid,  is  converted  into 
white  mercuric  oxalate  within  fifteen  minutes,  while  red  oxide  is  not 
acted  upon  by  oxalic  acid  under  the  same  conditions. 

When  mercuric  chloride  is  added  to  lime-water,  a  mixture  is 
formed  holding  in  suspension  yellow  mercuric  oxide;  this  mixture 
is  known  as  yellow-wash. 

Experiment  44.  Shake  a  small  knifepointful  of  mercurous  chloride  (calomel) 
with  50  c.c.  of  lime-water.  Note  that  the  chloride  instantly  turns  dark,  due  to 
formation  of  mercurous  oxide  (see  reaction  in  text).  The  lime-water  must  be 
in  excess. 

Add  about  1  c.c.  of  reagent  solution  of  mercuric  chloride  to  50  c.c.  of  lime- 
water  and  stir.  Yellow  mercuric  oxide  is  formed  at  once  (see  reaction  in  text). 
If  the  lime-water  is  not  in  excess,  the  precipitate  will  not  be  pure  yellow,  but 
whitish,  due  to  formation  of  an  oxychloride,  Hg2OCl2. 

Caustic  alkalies  produce  the  same  results  as  above,  but  any  excess  of  these 
stronger  alkalies  is  objectionable  for  the  purposes  for  which  these  "  washes  "  are 
used. 

Experiment  45.  Heat  some  mercuric  nitrate  in  a  porcelain  dish,  placed  in  a 
ftime  chamber,  until  red  fumes  no  longer  escape.  The  remaining  red  powder 
is  mercuric  oxide,  which,  by  further  heating,  may  be  decomposed  into  its  ele- 
ments. 

Mercurous  chloride,  Hydrargyrum  chloridum  mite,  HgCl  = 
233.68  (Calomel ,  Mild  chloride  of  mercury,  Subchloride  or  proto- 
chloride  of  mercury).  Mercurous  chloride,  like  mercurous  oxide, 
may  be  made  by  different  processes,  but  the  article  used  medicinally 
is  the  one  obtained  (except  it  be  otherwise  stated)  by  sublimation 
and  the  rapid  condensation  of  the  vapor  in  the  form  of  powder. 

It  is  made  either  by  subliming  a  mixture  of  mercuric  chloride 
and  mercury: 

HgCl,  +  Hg  =  2HgCl. 


SILVER— MERCURY.  339 

or  by  thoroughly  mixing  with  mercuric  sulphate  a  quantity  of  mer- 
cury equal  to  that  contained  in  the  sulphate ;  by  this  operation  mer- 
curous sulphate  is  obtained,  which  is  mixed  with  sodium  chloride, 
and  sublimed  from  a  suitable  apparatus  into  a  large  chamber,  so  that 
the  sublimate  may  fall  in  powder  to  the  floor : 

HgS04  -f  Hg  +  2NaCl  =  Na2SO4  +  2HgCl. 

Precipitated  calomel,  being  in  a  finer  state  of  subdivision,  acts 
more  energetically  when  used  medicinally.  It  is  obtained  by  pre- 
cipitation of  a  soluble  mercurous  salt  by  any  soluble  chloride: 

HgNO3  +  NaCl  =  NaNO8  +  HgCl. 

Mercurous  chloride,  made  by  either  process,  generally  contains 
traces  of  mercuric  chloride,  and  should,  therefore,  be  washed  with 
hot  water  until  the  washings  are  no  longer  acted  upon  by  ammonium 
sulphide  or  silver  nitrate. 

Mercurous  chloride  is  a  white,  impalpable,  tasteless  powder,  in- 
soluble in  water  and  alcohol ;  it  volatilizes  without  fusing  previously ; 
when  given  internally,  it  should  not  be  mixed  with  either  mineral 
acids,  alkali  bromides,  iodides,  hydroxides,  or  carbonates,  except  the 
action  of  the  decomposition  products  be  desired. 

Mercuric  chloride,  Hydrargyri  chloridum  corrosivum,  Hg-CL, 
—  268.86  (Corrosive  chloride  of  mercury,  Corrosive  sublimate,  Perchlo- 
ride  or  bichloride  of  mercury).  Made  by  thoroughly  mixing  mercuric 
sulphate  with  sodium  chloride,  and  subliming  the  mixture,  when 
mercuric  chloride  is  formed,  and  passes  off  in  white  fumes  which  are 
condensed  in  the  cooler  part  of  the  apparatus,  while  sodium  sulphate 

is  left : 

HgSO,  +  2NaCl  =  Na2SO4  +  HgCl2. 

Mercuric  chloride  is  a  heavy,  white  powder,  or  occurs  in  heavy, 
colorless,  rhombic  crystals  or  crystalline  masses;  it  is  soluble  in  16 
parts  of  cold  and  2  parts  of  boiling  water,  and  in  about  3  parts  of 
alcohol,  in  4  parts  of  ether,  and  in  about  14  parts  of  glycerin;  when 
heated,  it  fuses  and  is  volatilized ;  it  has  an  acrid,  metallic  taste,  an 
acid  reaction,  and  strongly  poisonous  and  antiseptic  properties. 

The  halogen  salts  of  mercury  are  very  little  ionized  in  solution.  On  this 
account,  mercuric  chloride  is  much  less  hydrolyzed  than  mercuric  nitrate,  that 
is,  there  is  not  so  much  tendency  to  precipitate  a  basic  salt.  Mercuric  chloride 
also  has  the  tendency  to  form  complex  salts.  Thus  sodium  chloride  increases  its 
solubility  in  water  and  causes  the  solution  to  become  neutral,  because  of  the 
formation  of  the  salt,  HgCl2.NaCl  or  NaHgCl3.  Mercuric  chloride  tablets  are 


340  METALS  AND  THEIR  COMBINATIONS. 

made  up  witih  sodium  chloride,  because  the  latter  prevents  the  formation  of  in- 
soluble chlorides  and  facilitates  solution,  although  the  activity  of  the  mercury 
compound  is  somewhat  lessened.  Mercuric  chloride  is  sometimes  used  as  a 
preservative  of  specimens.  It  forms  insoluble  compounds  with  albumin  and 
prevents  its  decay.  On  this  principle,  albumin  is  given  as  an  antidote  in  mer- 
curic chloride  poisoning. 

Mercurous  iodide,  Hydrargyri  iodidum  flavum,  Hgl  =  324.4 
(  Yellow  iodide,  green  iodide,  or  protiodide  of  mercury).  Both  iodides 
of  mercury  may  be  obtained  either  by  rubbing  together  mercury  and 
iodine  in  the  proportions  represented  by  the  respective  atomic  weights, 
or  by  precipitation  of  soluble  mercurous  or  mercuric  salts  by  potas- 
sium iodide. 

According  to  the  U.  S.  P.,  mercurous  iodide  is  made  by  the  pre- 
cipitation of  a  solution  of  mercurous  nitrate,  to  which  some  nitric  acid 
has  been  added,  by  a  solution  of  potassium  iodide  : 

HgNO3  +  KI  =  KNO3  H-  Hgl. 

The  precipitate  is  collected  on  a  filter,  well  washed  with  water  and 
alcohol,  and  dried  between  paper  at  a  temperature  not  exceeding 
40°  C.  (104°  F.).  During  the  whole  operation  light  should  be  ex- 
cluded as  much  as  possible,  as  it  decomposes  the  compound. 

Mercurous  iodide  is  a  yellow,  tasteless  powder,  almost  insoluble  in 
water.  It  is  easily  decomposed  into  mercuric  iodide  and  mercury, 
becoming  darker  and  assuming  a  greenish -yellow  to  green  tint,  due 
to  the  admixture  of  metallic  mercury,  which,  in  a  finely  divided 
state  is  blue,  and  consequently  causes  a  greenish  mixture  with  the 
yellow  iodide.  (Plate  IV.,  5.) 

Mercuric  iodide,  Hydrargyri  iodidum  rubrum,  Hg-I2  — 45O.3 
(Red  iodide  or  biniodide  of  mercury).  Made  by  mixing  solutions  of 
potassium  iodide  and  mercuric  chloride,  when  a  pale-yellow  precipi- 
tate is  formed,  turning  red  immediately  (Plate  IV.,  6) : 

HgCl2  +  2KI  =  2KC1  +  HgI2. 

Mercuric  iodide  is  soluble  both  in  solution  of  potassium  iodide  and 
mercuric  chloride,  for  which  reason  an  excess  of  either  substance  will 
cause  a  loss  of  the  salt  when  prepared.  It  is  a  scarlet-red,  tasteless 
powder,  almost  insoluble  in  water  and  but  slightly  soluble  in  alcohol ; 
on  heating  or  subliming  it  turns  yellow  in  consequence  of  a  molecular 
change  which  takes  place ;  on  cooling,  and,  more  quickly,  on  pressing 
or  rubbing  the  yellow  powder,  it  reassumes  the  original  condition 
and  the  red  color. 


SILVER— MERCUHY.  341 

When  mercuric  iodide  is  dissolved  in  potassium  iodide  solution,  a  complex 
salt  is  formed,  HgI2.2KI,  or  K2HgI4,  from  which  many  of  the  usual  reagents  fail 
to  precipitate  the  mercury.  For  example,  caustic  potash  has  no  effect  on  the 
compound,  and  such  an  alkaline  solution  is  known  as  Nessler's  reagent.  This 
reagent  gives  a  yellow  color  with  traces  of  ammonia,  and  a  brown  precipitate 
with  larger  amounts : 

2HgI2    +    4NH3  Hg2NI    +    3NHJ. 

Nessler's  reagent  is  used  in  water  analysis  for  detecting  traces  of  ammonia. 
The  compound,  Hg2NI,  is  called  dimercur-ammonium  iodide. 

Mercuric  sulphate,  Hg-SO4.  When  mercury  is  heated  with  strong 
sulphuric  acid  (the  presence  of  nitric  acid  facilitates  the  formation) 
chemical  action  takes  place  between  the  two  substances,  sulphur 
dioxide  being  liberated  and  mercuric  sulphate  formed,  which  upon 
evaporation  of  the  solution  is  obtained  as  a  heavy,  white,  crystalline 
powder : 

Hg  +  2H2S04  =  HgS04  +  2H20  +  SO2. 

Yellow  mercuric  subsulphate,  Hg-SO4.(Hg-O)2  (Basic  mercuric 
sulphate,  Turpeth  mineral,  Mercuric  oxy-sulphate).  When  mercuric 
sulphate,  prepared  as  directed  above,  is  thrown  into  boiling  water,  it 
is  decomposed  into  an  acid  salt  which  remains  in  solution,  and  a  basic 
salt  which  is  precipitated.  As  shown  by  its  composition,  it  may  be 
looked  upon  as  mercuric  sulphate  in  combination  with  mercuric  oxide. 
It  is  a  heavy,  lemon-yellow,  tasteless  powder,  almost  insoluble  in 
water. 

Mercurous  sulphate,  Hg2SO4.  When  mercuric  sulphate  is  triturated 
with  a  sufficient  quantity  of  mercury,  direct  combination  takes  place, 
and  the  mercurous  salt  is  formed  : 

HgS04  +  Hg  =  Hg2S04. 

Nitrates  of  mercury.  Mercurous  nitrate,  HgNO3,  and  Mer- 
curic nitrate,  Hg(NO3)2,  may  both  be  obtained  as  white  salts  by  dis- 
solving mercury  in  nitric  acid.  The  relative  quantities  of  the  two 
substances  present  determine  whether  mercurous  or  mercuric  nitrate 
be  formed.  If  mercury  is  present  in  excess  the  mercurous  salt,  if  nitric 
acid  is  present  in  excess  the  mercuric  salt,  is  formed,  the  latter  espe^ 
cially  on  heating.  Both  salts  are  white  and  soluble  in  water  contain- 
ing free  acid.  Water  alone  causes  decomposition  of  the  nitrates, 
similar  to  that  of  the  sulphates,  resulting  in  the  formation  of  insoluble 
basic  salts,  the  composition  of  which  depends  on  the  relative  propor- 
tions of  the  mercury  salt  and  water  used. 

Experiment  46.— Heat  gently  a  small  globule  (about  1  gramme)  of  mercury 
with  2  c.c.  of  nitric  acid  until  red  fumes  cease  to  escape.  If  some  of  the  mer- 


342  METALS  AND  THEIR   COMBINATIONS. 

cury  remains  undissolved,  the  solution  will  deposit  crystals  of  mercurous 
nitrate  on  cooling.  Use  some  of  the  solution,  after  being  diluted  with  much 
water,  for  mercurous  tests.  Use  another  portion  as  follows :  Heat  the  solution, 
or  some  of  the  crystals,  with  about  an  equal  weight  of  nitric  acid  until  no  more 
red  fumes  escape.  Add  to  a  few  drops  of  the  diluted  liquid  a  little  hydro- 
chloric acid,  which,  if  the  conversion  of  the  mercurous  into  mercuric  salt  has 
been  complete,  will  give  no  precipitate.  If,  however,  one  should  be  formed,  the 
solution  is  heated  with  more  nitric  acid  until  no  precipitate  is  formed  by  hydro- 
chloric acid,  when  the  solution  is  evaporated  and  set  aside  for  crystallization. 
The  respective  changes  may  be  represented  by  the  following  equations : 

3Hg  +  4HN03  ==  3HgNO3       +  2H2O  +  NO  ; 
3HgNO3  +  4HN03  =  3Hg(NO3)2  -f  2H2O  +  NO. 

Mercuric  sulphide,  HgS.  This  compound  has  been  mentioned  as 
the  chief  ore  of  mercury,  occurring  crystallized  as  cinnabar,  which 
has  a  red  color  (Plate  IV.,  2).  The  same  compound  may,  however, 
be  obtained  by  passing  hydrogen  sulphide  through  mercuric  solutions, 
when  at  first  a  white  precipitate  is  formed  (a  double  compound  of  the 
sulphide  of  mercury  in  combination  with  the  mercuric  salt),  which 
soon  turns  black  (Plate  IV.,  1) : 

HgCl2  +  H-jS  =  2HC1  +  HgS. 

The  black,  amorphous,  mercuric  sulphide  may  be  converted  into  the 
red,  crystallized  variety  by  sublimation,  and  is  then  the  preparation 
known  as  red  sulphide  of  mercury,  cinnabar,  or  vermilion.  It  forms 
brilliant  dark-red  crystalline  masses,  or  a  fine  bright  scarlet  powder, 
which  is  insoluble  in  water,  hydrochloric  or  nitric  acid,  but  soluble 
in  nitro-hydrochloric  acid. 

Mercuric  and  mercurous  sulphides  may  be  made  also  by  triturating 
the  elements  mercury  and  sulphur  in  the  proper  proportions,  when 
they  combine  directly. 

Ammoniated  mercury,  Hydrargyrum  ammoniatum,  NH^HgCl 
=  249.61  (  White,  precipitate,  Mercuric-ammonium  chloride).  This  com- 
pound is  made  by  pouring  solution  of  mercuric  chloride  into  ammonia 
water,  when  a  white  precipitate  falls,  which  is  washed  with  highly 
diluted  ammonia  water  and  dried  at  a  low  temperature  : 

HgCl2    +    2NH4OH    ==    NH2HgCl    +    NH4C1    +    2H2O. 

As  shown  by  the  composition  of  this  compound,  it  may  be  re- 
garded as  ammonium  chloride,  NH4C1,  in  which  two  atoms  of  hydro- 
gen have  been  replaced  by  one  atom  of  the  bivalent  mercury.  The 
mercuric-ammonium  salts  are  of  a  different  type  from  those  combina- 


SIL  VER—MERCUR  Y. 


343 


tions  formed  when  copper,  silver,  zinc,  etc.,  salts  are  dissolved  in  am- 
monia water.  The  former  are  all  insoluble  in  water. 

Ammoniated  mercury  is  a  white,  tasteless,  insoluble  powder. 

Mercurous  salts  with  ammonia  water  give  black  insoluble  precipi- 
tates consisting  of  a  mixture  of  mercuric-ammonium  salts  and  mercury, 
which  causes  the  black  appearance.  For  mercurous  chloride  and 
nitrate  the  reactions  are  : 

2HgCl  +   2NH3   =  HgNH2.Cl       -f   Hg  -f   NH4C1. 
2HgN03  -f   2NH3   =  HgNH2.N03  +   Hg  +   NH4NO3. 

It  should  be  noted  that  in  the  case  of  mercury  salts,  ammonia  water 
does  not  precipitate  hydroxides,  as  it  does  in  other  cases. 

Tests  for  mercury. 


Mercurous  salts. 

(Mercurous  nitrate,  HgNO3  may 
be  used. ) 


1.  Hydrogen  sul- 
phide, or  ammo- 
nium sulphide. 


2.  Potassium  iodide. 


3.  Potassium  or  so- 
dium hydroxide. 

4.  Ammonium   hy- 
droxide. 


5.  Potassium  or  so- 
dium carbonate. 

6.  Hydrochloric 
acid  or  soluble 
chlorides. 


Black  precipitate  of  mercuric 
sulphide,  with  mercury. 
2HgN03  -f  HaS  = 
2HN03  +  HgS  +  Hg. 

Green  precipitate  of  mercurous 
iodide  (Plate  IV.,  7): 


KN03  +  Hgl. 

Dark-brown  precipitate  of  mer 
curous  oxide,  Hg2O  (Plate 
IV.,  5). 

Black  precipitate  of  a  mixture 
of  mercury  and  mercuric-am- 
monium chloride  (see  expla- 
nation above). 

Yellowish  precipitate  of  mer- 
curous carbonate,  which  is 
unstable. 

White  precipitate  of  mercurous 
chloride  is  produced : 
HgN03  +  HC1  = 
HN03  -f-  HgCl. 


Mercuric  salts. 

(Mercuric  chloride,  HgCl2,  may 
be  used.) 

Black  precipitate  of  mercuric 
sulphide.  (Precipitate  may  be 
white  or  gray,  with  an  insuffi- 
cient quantity  of  the  reagent.) 
(See  above)  (Plate  IV.,  1.) 

Red  precipitate  of  mercuric 
iodide  (See  above.)  (Plate 
IV,  6.) 

Yellow  precipitate  of  mercuric 

oxide      HgO.      (See  above.) 

(Plate  IV.,  3.) 
White  precipitate  of  a  mercuric 

ammonium    salt    is   formed. 

( See  explanation  above.) 


Brownish-red  precipitate  of 
basic  mercuric  carb.,  mixed 
with  mercuric  oxychloride. 

No  change. 


7.  Stannous-  chloride  produces,  in  solutions  of  mercury,  a  white 
precipitate,  which  turns  dark-gray  on  heating  with  an  excess  of  the 
reagent.  The  reaction  is  due  to  the  strong  reducing  or  deoxidizing 
property  of  the  stannous  chloride,  which  itself  is  converted  into  stannic 
chloride,  while  the  mercury  salt  is  first  converted  into  a  mercurous 
salt  and  afterward  into  metallic  mercury  : 

2HgCl2  +  SnCl2  =  2HgCl  -f  SnCl4; 
2HgCl  +  SnCl2  =  2Hg      +  SnCl,. 


344 


METALS  AND  THEIR  COMBINATIONS. 


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MERCURY.    SILVER. 


PLATE  IV. 


Mercuric  sulphide,  precipitated  fro 
mercuric  solutions  by  hydrogen  sulphid 


Mercuric  sulphide,  Cinnabar. 


Yellow  mercuric  oxide,  precipitat* 
from  mercuric  solutions  by  potassium  h 
droxide. 


Red    mercuric    oxide,    obtained    1 
heating  mercuric  nitrate. 


Mercurous  oxide,  precipitated  fro 
mercurous  solutions  by  potassium  hydro: 
ide. 

Silver  sulphide,  precipitated  fro 
silver  solutions  by  hydrogen  sulphide. 


flercuric    iodide,    precipitated    froi 
mercuric  solutions  by  alkali  iodides. 


Mercurous  iodide,  precipitated  froi 
mercurous  solutions  by  alkali  iodides. 


8 


Mercuric  solutions  with  ammoniui 
hydroxide,  flercurous  solutions  wit 
soluble  chlorides.  Silver  solutions  wit 
soluble  chlorides. 


A.Hoen&CftLith 


ARSENIC.  345 

8.  Dry  mercury  compounds,  when  mixed  with  sodium  carbonate 
and  potassium  cyanide,  and  heated  in  a  narrow  test-tube,  are  decom- 
posed with  liberation  of  metallic  mercury,  which  condenses  in  small 
globules  in  the  cooler  part  of  the  tube. 

9.  A  piece  of  bright  metallic  copper  when  placed  in  a  slightly  acid 
mercury  solution  becomes  coated  with   a  dark  film  of  metallic  mer- 
cury, which  by  rubbing  becomes  bright  and  shining,  and   may  be 
volatilized  by  heat.      (See  Solution  tension,  page  319.) 

10.  All  compounds  of  mercury  are  completely  volatilized  by  heat, 
either  with  or  without  decomposition. 

Tests  2,  4,  7,  8,  and  9  will  show  the  presence  of  mercury  in  any  of 
its  compounds.  Those  that  are  insoluble  in  water  may  be  dissolved 
by  a  little  concentrated  hydrochloric  with  a  few  drops  of  nitric  acid, 
forming  mercuric  chloride.  Excess  of  acid  is  removed  by  evaporation . 

Antidotes.  Albumen  (white  of  egg),  of  which,  however,  not  too  much  should 
be  given  at  one  time,  lest  the  precipitate  formed  by  the  mercuric  salt  and 
albumin  be  redissolved.  The  antidote  should  be  followed  by  an  emetic  to 
remove  the  albuminous  mercury  compound. 

Ionic  conditions.  The  simple  mercury  compounds  give  mercurous  ions,  Hg", 
and  mercuric  ions,  Hg",  which  show  different  behaviors  toward  reagents,  as 
seen  in  the  tests  above.  The  mercury  ions  are  colorless,  and  are  not  formed 
extensively  from  any  compound.  The  disinfecting  and  poisonous  properties  of 
mercury  compounds  depend  upon  the  presence  of  the  ions.  Mercuric  chloride 
in  the  dry  state  is  inactive,  and  its  solution  in  alcohol  or  ether  is  almost  inert 
as  a  disinfectant,  because  there  are  practically  no  mercury  ions  formed. 

Salts  in  general  have  a  high  degree  of  ionization,  but  salts  of  mercury  and 
cadmium  are  remarkable  exceptions.  For  this  reason  mercury  salts  show  some 
peculiar  behaviors.  For  example,  the  halogen  salts  of  mercury  dissociate  so 
little  (the  bromide  and  iodide  less  than  the  chloride)  that  they  are  scarcely 
affected  by  sulphuric  or  nitric  acid.  Sodium  chloride  with  sulphuric  acid  gives 
hydrochloric  acid,  and  with  nitric  acid  it  gives  chlorine.  Mercuric  cyanide, 
Hg(CN)2,  is  so  minutely  dissociated,  that  the  presence  of  either  Hg"  ions  or 
(CN)'  ions  cannot  be  shown  by  precipitation  with  many  reagents.  Thus,  silver 
nitrate  does  not  precipitate  the  (ON)7  ions,  as  AgCN,  nor  do  alkalies  precipitate 
Hg*  *  ions,  as  HgO.  But  hydrogen  sulphide  precipitates  mercury  from  any  of 
its  soluble  compounds,  because  mercuric  sulphide  is  practically  completely  in- 
soluble and  unionized.  It  is  for  this  reason  that  the  sulphide  is  not  dissolved 
by  any  acid,  even  when  concentrated  and  heated,  except  nitrohydrochloric. 

Mercury  is  deposited  from  all  its  compounds,  whether  soluble  in  water  or 
not,  by  the  metals  higher  up  in  the  electrochemical  series.  Hence,  it  is  not 
advisable  to  use  vermilion  in  paint  to  be  applied  to  metallic  surfaces.  Eed  lead 
is  better  for  this  purpose. 

The  complex  salts  which  mercuric  chloride  forms  with  alkali  chlorides  dis- 
sociate in  part  so  that  mercury  is  contained  in  the  complex  negative  ion,  and 
to  this  extent  loses  its  disinfectant  property.  The  ionization  equation  for  this 


346  METALS  AND   THEIR   COMBINATIONS. 

type  of  compound  is  illustrated  in  the  case  of  the  sodium  compounds,  NaCl.- 
HgCl2  or  NaHgCl3,  and  2NaCl.HgCl2  or  Na2HgCl4: 

NaHgCl3  Z±     Na*  -f  HgCL,'; 
Na2HgCl4  ^±  2Na*  +  HgCl/'. 

But  there  is  considerable  dissociation  also  into  Hg*  •  ions  and  Cl'  ions.  Hence 
with  not  too  much  sodium  chloride  present  and  in  very  dilute  solution,  the 
mercuric  chloride  tablets  containing  sodium  or  ammonium  chloride  do  not 
lose  materially  in  germicidal  power,  since  a  relatively  large  proportion  of  the 
ions  are  the  active  Hg*  •  ions. 

The  complex  potassium  mercuric  iodide,  K2HgI4,  gives  K*  ions  and  Hgl/7 
ions,  but  very  few  Hg*  *  ions.  Hence  the  failure  of  some  reagents,  as  alkalies 
and  carbonates,  to  give  a  precipitate  in  a  solution  of  the  compound. 

32.  ARSENIC. 
As  =  74.4. 

General  remarks  regarding1  the  metals  of  the  arsenic  group. 
The  metals  belonging  to  either  of  the  five  groups,  considered  hereto- 
fore, show  much  resemblance -to  each  other  in  their  chemical  prop- 
erties, and  consequently  in  their  combinations.  This  is  much  less 
the  case  among  the  six  metals  (As,  Sb,  Sn,  Au,  Pt,  Mo)  which  are 
classed  together  in  this  group.  In  fact,  the  chief  resemblance  which 
unites  these  metals  is  the  insolubility  of  their  sulphides  in  dilute 
acids  and  the  solubility  of  these  sulphides  in  ammonium  sulphide 
(or  alkali  hydroxides),  with  which  they  form  soluble  double  com- 
pounds ;  the  oxides  have  also  a  tendency  to  form  acids.  In  most 
other  respects  no  general  resemblance  exists  between  these  metals. 
On  the  other  hand,  arsenic  and  antimony  have  many  properties  in 
common,  and  resemble  in  many  respects  the  non-metallic  elements 
phosphorus  and  nitrogen,  as  may  be  shown  by  a  comparison  of  their 
hydrides,  oxides,  acids,  and  chlorides. 

QUESTIONS. — How  is  silver  obtained  from  the  native  ores,  and  how  may  it 
be  prepared  from  silver  coin?  State  of  silver  nitrate:  its  composition,  mode 
of  preparation,  properties,  and  names  by  which  it  is  known.  Give  analytical 
reactions  for  silver.  How  is  mercury  found  in  nature ;  how  is  it  obtained  from 
the  native  ore ;  what  are  its  physical  and  chemical  properties?  Mention  the 
three  oxides  of  mercury;  how  are  they  made,  what  is  their  composition,  what 
is  their  color  and  solubility  ?  State  of  the  two  chlorides  of  mercury :  their 
names,  composition,  mode  of  preparation,  solubility,  color,  and  other  proper- 
ties. Mention  the  same  of  the  two  iodides,  as  above,  for  the  chlorides.  State 
the  difference  between  mercuric  sulphate,  basic  mercuric  sulphate,  and  mer- 
curous  sulphate.  What  is  formed  when  ammonium  hydroxide,  calcium  hydrox- 
ide, potassium  or  sodium  hydroxide  is  added  to  either  mercurous  or  mercuric 
chloride  ?  Give  tests  answering  for  any  mercury  compound,  and  tests  by  which 
mercuric  compounds  may  be  distinguished  from  mercurous  compounds. 


ARSENIC.  347 

NH3  N203  NA  NC13. 

PH3  P20S  PA  H3P04  PC13. 

AsH3  As2O3  As2O5  H3AsO4  AsCl3. 

SbH.  SbA  Sb205  SbCl3. 

Arsenic.  Found  in  nature  sometimes  in  the  native  state,  but 
generally  as  sulphide  or  arsenide.  One  of  the  most  common  arsenic 
ores  is  the  arsenio-sulphide  of  iron,  or  mispiekel,  FeSAs.  Realgar  is 
the  native  red  sulphide,  As2S2,  and  orpiment  or  aurijrigment,  the  native 
yellow  sulphide,  As2S3.  Arsenides  of  cobalt,  nickel,  and  other  metals 
are  not  infrequently  met  with  in  nature.  Certain  mineral  waters 
contain  traces  of  arsenic  compounds. 

Arsenic  may  be  obtained  easily  by  heating  arsenous  oxide  with 
charcoal,  or  by  allowing  vapors  of  arsenous  oxide  to  pass  over  char- 
coal heated  to  redness  : 

AsA  +  3C  =  SCO  +  2As. 

In  both  cases  the  arsenic,  when  liberated  by  the  reducing  action  of 
the  charcoal,  exists  in  the  form  of  vapor,  which  condenses  in  the 
cooler  part  of  the  apparatus  as  a  steel-gray  metallic  mass,  which 
when  exposed  to  the  amospheric  air,  loses  the  metallic  lustre  in  conse- 
quence of  the  formation  of  a  film  of  oxide. 

Experiment  47.  Eub  together  in  a  mortar  a  small  quantity  of  arsenous  oxide 
and  about  ten  times  as  much  charcoal.  Heat  the  mixture  in  a  covered  porce- 
lain crucible  with  a  small  flame.  After  a  time  examine  the  cover  for  a  dark 
deposit  of  arsenic. 

When  pure,  arsenic  is  odorless  and  tasteless ;  it  is  very  brittle,  and 
volatilizes  unchanged  and  without  melting  when  heated  to  180°  C. 
(356°  F.),  without  access  of  air.  Heated  in  air,  it  burns  with  a 
bluish-white  light,  forming  arsenous  oxide.  Although  insoluble  in 
water,  yet  water  digested  with  arsenic  soon  contains  some  arsenous 
acid  in  solution,  the  oxide  of  arsenic  being  formed  by  oxidation  of 
the  metal  by  the  oxygen  absorbed  in  the  water. 

Arsenic  is  used  in  the  metallic  state  as  fly-poison,  and  in  some 
alloys,  chiefly  in  shot,  an  alloy  of  lead  and  arsenic. 

The  molecule  of  arsenic  contains  four  atoms,  and  not  two,  like 
most  elements.  It  is  trivalent  in  some  compounds,  quinquivalent  in 
others. 

Although  arsenic  is  grouped  with  the  metals  in  the  analytical  system  of 
classification,  in  nearly  all  respects  it  behaves  like  a  non-metal  and  should  prop- 
erly be  classed  as  such.  The  oxides  have  only  acidic  character,  and  do  not  form 
salts  with  acids,  as  nitrates,  sulphates,  etc.  The  chloride,  AsCl3,  can  be  obtained, 


348  METALS  AND  THEIR  COMBINATIONS. 

but  it  decomposes  at  once  in  water,  giving  arsenous  acid.  It  exists  in  solution 
only  in  the  presence  of  excess  of  hydrochloric  acid.  When  the  solution  is 
evaporated  to  dryness,  arsenous  oxide  remains. 

Arsenic  trioxide,  Arseni  trioxidum,  As2O3  =  196.44  (Arsenous 
oxide.  White  arsenic,  Arsenous  anhydride,  improperly  Arsenous  acid). 
This  compound  is  frequently  obtained  as  a  by-product  in  metallurgical 
operations  during  the  manufacture  of  metals  from  ores  containing 
arsenic  Such  ores  are  roasted  (heated  in  a  current  of  air),  when 
arsenic  is  converted  into  arsenous  oxide,  which,  at  that  temperature. 
is  volatilized  and  afterward  condensed  in  chambers  or  long  flues. 

Arsenous  oxide  is  a  heavy,  white  solid,  occurring  either  as  an 
opaque,  slightly  crystalline  powder,  or  in  transparent  or  semi-trans- 
parent masses  which  frequently  show  a  stratified  appearance; 
recently  sublimed  arsenous  oxide  exists  as  the  amorphous  semi- 
transparent  glassy  mass  known  as  vitreous  arsenous  oxide,  which 
gradually  becomes  opaque  and  ultimately  resembles  porcelain.  This 
change  is  due  to  a  rearrangement  of  the  molecules  into  crystals  which 
can  be  seen  under  the  microscope. 

The  two  modifications  of  arsenous  oxide  differ  in  their  solubility 
in  water,  the  amorphous  or  glassy  variety  dissolving  more  freely  than 
the  crystallized.  One  part  of  arsenous  oxide  dissolves  in  from  30  to 
80  parts  of  cold  and  in  15  parts  of  boiling  water,  the  solution  having 
at  first  a  faint  acrid  and  metallic,  and  afterward  a  sweetish  taste. 
This  solution  contains  the  arsenous  oxide  not  as  such,  but  as  arsenous 
add,  H3AsO3,  which  compound,  however,  cannot  be  obtained  in  an 
isolated  condition,  but  is  known  in  solution  only  : 

3H20  =  2H3As03. 


A  second  arsenous  acid,  termed  met-arsenous  acid  or  meta-arsenous  acid, 
s02,  is  known  in  some  salts,  as,  for  instance,  in  sodium  metarsenite,  NaAsO* 
which  salt  may  be  obtained  by  the  action  of  arsenous  oxide  on  the  carbonate, 
bicarbonate,  or  hydroxide  of  sodium  : 

As203  +  2NaOH  =  2NaAsO2  +  H2O. 

When  heated  to  about  218°  C.  (424°  F.)  arsenous  oxide  is  volatil- 
ized without  melting;  the  vapors,  when  condensed,  form  small, 
shining^  eight-sided  crystals;  when  heated  on  charcoal,  it  is  deoxi- 
dized, giving  off,  at  the  same  time,  an  odor  resembling  that  of  garlic. 

Arsenous  oxide  is  frequently  used  in  the  arts  and  for  manufacturing 
purposes,  as,  for  instance,  in  the  manufacture  of  green  colors,  of 
opaque  white  glass,  in  calico-printing,  as  a  powerful  antiseptic  for 
the  preservation  of  organic  objects  of  natural  history,  and,  finally,  as 
the  substance  from  which  all  arsenic  compounds  are  obtained. 


ARSENIC.  349 

The  official  Solution  of  arsenous  acid,  Liquor  acidi  arxcnosi,  is  a 

1  per  cent,  solution  of  arsenous  oxide  in  water  to  which  5  per  cent, 
of  diluted  hydrochloric  acid  has  been  added. 

The  official  Solution  of  potassium  arsenite,  Liquor  potassii  arsenitis,  or 
Fowler's  solution,  is  made  by  dissolving  1  part  of  arsenous  oxide  and 

2  parts  of  potassium  bicarbonate  in  94  parts  of  water  and  adding 

3  parts  of  compound  tincture  of  lavender ;  the  solution  contains  the 
arsenic  as  potassium  met-arsenite. 

Arsenic  oxide,  As2O5  (Arsenic  pentoxide,  Arsenic  acid  anhydride). 
When  arsenous  oxide  is  heated  with  nitric  acid,  it  becomes  oxidized 
and  is  converted  into  arsenic  acid,  H3AsO4,  from  which  the  water 
may  be  expelled  by  further  heating,  when  arsenic  oxide  is  left : 
2H3AsO4  =  As2O5  +  3H2O. 

Arsenic  oxide  is  a  heavy,  white,  solid  substance  which,  in  contact 
with  water,  is  converted  into  arsenic  acid.  This  acid  resembles  phos- 
phoric acid  in  composition,  but  diifers  from  it  in  not  forming  pyro- 
and  metarsenic  acids.  Arsenic  acid  when  moderately  heated  loses  all 
its  water  and  leaves  the  pentoxide,  which  at  higher  heat  is  decom- 
posed into  the  trioxide  and  oxygen.  Phosphoric  acid,  however,  when 
heated  is  converted  into  metaphosphoric  which  can  be  volatilized, 
and  phosphorus  pentoxide  does  not  decompose  by  heating.  Sodium 
pyroarsenate,  perhaps,  is  formed  when  sodium  arsenate  is  heated, 
but  when  the  mass  is  dissolved  in  water  arsenate  is  formed  at  once, 
whereas  the  pyrophosphate  can  be  crystallized  from  water. 

Arsenic  oxide  and  arsenic  acid  are  used  largely  as  oxidizing  agents 
in  the  manufacture  of  aniline  colors. 

Disodium  hydrogen  arsenate,  Sodii  arsenas,  Na2HAsO4.7H2O 
=  3O9.84  (Sodium  arsenate).     This  salt  is  made  by  fusing  arsenous 
oxide  with  carbonate  and  nitrate  of  sodium. 

As2O3  -f  2NaNO3  +  Na2CO3  =  Na4As2O7  +  N2O3  +  CO,. 

Sodium  pyroarsenate  is  formed,  nitrogen  trioxide  and  carbon  dioxide 
escaping.  By  dissolving  in  water  and  crystallizing,  the  official  salt  is 
obtained  in  colorless,  transparent  crystals  : 

Na4As207  -f  15H2O  =  2(Na2HAsO4.7H2O). 

Exsiccated  sodium  arsenate,  Sodii  arsenas  exsiceatus,  Na2HAsO4,  is 
the  product  obtained  by  driving  off  all  the  water  of  crystallization  at 
150°  C.  (302°  F.).  Liquor  sodii  arsenatis  is  a  1  per  cent,  solution  of 


350  METALS  AND   THEIR   COMBINATIONS. 

exsiccated  sodium  arsenate  in  water,  corresponding  to  1.68  per  cent, 
of  the  crystallized  salt. 

Lead  arsenate,  Pb3(AsO4)2,  is  used  for  spraying  plants  to  exterminate 
moths.  It  is  a  white,  fusible  powder,  insoluble  in  water,  ammonia,  and  ammo- 
nium salts.  It  is  obtained  by  precipitation  of  basic  lead  acetate  (subacetate) 
with  sodium  arsenate,  or  lead  nitrate  with  excess  of  sodium  arsenate : 

3Pb(NO3)2  +  4Na2HAsO4  =  Pb3(AsO4)2  -f  6NaNO3  +  2NaH2AsO4. 

Hydrogen  arsenide,  AsH3  .(Arsine,  Arsenetted  or  arseniuretted 
hydrogen).  This  compound  is  formed  always  when  either  arsenous 
or  arsenic  oxides  or  acids,  or  any  of  their  salts,  are  brought  in  con- 
tact with  nascent  hydrogen,  for  instance,  with  zinc  and  diluted 
sulphuric  acid,  which  evolve  hydrogen  : 

As2O3  +  12H  =  2AsH3  +  3H2O. 
As-A  +  16H  =  2AsH3  +  5H2O. 
AsCl3  +  6H  =  AsH3  +  3HC1. 

Hydrogen  arsenide  is  a  colorless,  highly  poisonous  gas,  having  a 
strong  garlic  odor.  Ignited,  it  burns  with  a  bluish  flame,  giving  off 
white  clouds  of  arsenous  oxide  : 

2AsH3  +  6O  =  As2O3  +  3H2O. 

When  a  cold  plate  (porcelain  answers  best)  is  held  in  the  flame  of 
arsenetted  hydrogen,  a  dark  deposit  of  metallic  arsenic  (arsenic  spots) 
is  produced  upon  the  plate  (in  a  similar  manner  as  a  deposit  of 
carbon  is  produced  by  a  common  luminous  flame).  The  formation  of 
this  metallic  deposit  may  be  explained  by  the  fact  that  the  heat  of  the 
flame  decomposes  the  gas,  and  that,  furthermore,  of  the  two  liberated 
elements,  arsenic  and  hydrogen,  the  latter  has  the  greater  affinity  for 
oxygen.  In  the  centre  of  the  flame,  to  which  but  a  limited  amount 
of  oxygen  penetrates,  the  latter  is  taken  up  by  the  hydrogen,  arsenic 
being  present  in  the  metallic  state  until  it  burns  in  the  outer  cone  of 
the  flame.  It  is  this  liberated  arsenic  which  is  deposited  upon  a  cold 
substance  held  in  the  flame. 

Arsenetted  hydrogen,  when  heated  to  redness,  is  decomposed  into 
its  elements  ;  by  passing  the  gas  through  a  glass  tube  heated  to  red- 
ness, the  liberated  arsenic  is  deposited  in  the  cooler  part  of  the  tube, 
forming  a  bright  metallic  ring. 

Sulphides  of  arsenic.  Three  sulphides  of  arsenic  are  known.  Two 
have  been  mentioned  above  as  the  native  disulphide  or  realgar,  As2S2, 


ARSENIC.  351 

and  the  bisulphide  or  orpiment,  As2S3.  Bisulphide  of  arsenic  is  an 
orange-red,  fusible,  and  volatile  substance,  used  as  a  pigment;  it 
may  be  made  by  fusing  together  the  elements  in  the  proper  propor- 
tions. Trisulphide  is  a  golden-yellow,  fusible,  and  volatile  substance, 
which  also  may  be  obtained  by  fusing  the  elements,  or  by  precipitating 
an  arsenic  solution  by  hydrogen  sulphide  (Plate  V.,  1). 

The  pentasulphide,  As2S5,  has  the  same  color  as  the  trisulphide,  and 
is  most  readily  obtained  by  acidifying  a  solution  of  a  sulph-arsenate : 

2(NH4)3AsS4    4-    6HC1  2H3AsS4    +    6NH4C1. 

2H3AsS4    =    3H2S          +    As2S5. 

The  tri-  and  pentasulphide  of  arsenic  have  acid  properties,  similar  to 
the  corresponding  oxides.  They  unite  with  alkali  sulphides  to  form 
soluble  meta-sulph-arsenites  and  sulph-arsenates  : 

As.2S3    +    (NH4)2S      =    2NH4AsS2. 
As2S5    +    3(NH4)2S    =  •  2(NH4)3AsS4. 

When  the  trisulphide  is  dissolved  in  a  solution  of  a  polysulphide 
(yellow  ammonium  sulphide),  a  sulph-arsenate  is  formed, 

As2S3    4-    3(NH4)2S    4-    S,    =       2(NH4)3AsS4, 

from  which  acids  precipitate  the  pentasulphide.  Both  sulphides  are 
also  soluble  in  solutions  of  alkali  hydroxides  or  carbonates,  forming  a 
mixture  of  met-arsenite  and  meta-sulph-arsenite,  and  arsenate  and 
sulph-arsenate  respectively. 

Arsenous  iodide,  Arseni  iodidum,  AsI3  =  454.5  (Iodide  of  arsenic),  may 
be  obtained  by  direct  combination  of  the  elements,  and  forms  orange-red  crys- 
talline masses,  soluble  in  water  and  alcohol,  but  decomposed  by  boiling  with 
either  of  these  liquids.  It  is  used  in  the  official  preparation,  Solution  of  arsenous 
and  mercuric  iodides,  Donovan's  solution,  which  is  made  by  dissolving  one  part 
each  of  arsenous  iodide  and  mercuric  iodide  in  98  parts  of  water. 

Tests  for  arsenic. 

(For  arsenous  compound,  use  a  solution  of  arsenous  oxide  made  by  dissolving  0.5 
gramme  in  100  c.c.  of  hot  water  and  allowing  to  cool ;  for  arsenic  compound,  use  a  5 
per  cent,  solution  of  sodium  arsenate.) 

1.  Hydrogen  sulphide  produces  in  the  solution  of  arsenous  acid  a 
yellowish  coloration,  but  no  precipitate.  This  is  due  to  the  fact  that 
the  arsenic  trisulphide  remains  in  solution  in  the  colloidal  state  and  is 
precipitated  only  after  a  long  time.  Addition  of  some  hydrochloric 
acid  causes  precipitation  immediately  of  the  yellow  trisulphide  (Plate 

V,  1): 

2H3AsO3    4-    3H8S    ~    6H.p    4-    As2S3. 


352  METALS  AND   THEIR   COMBINATIONS. 

When  a  rapid  stream  of  hydrogen  sulphide  is  passed  into  a  hot  acid-. 
ified  solution  of  an  arsenate,  a  yellow  precipitate  of  arsenic  pentasul- 
phide  is  gradually  formed  : 


2H3AsO4    +    5H2S  8H2O     +     As2S5. 

Solution  of  ammonium  sulphide  or  caustic  alkali  readily  dissolves 
both  sulphides  of  arsenic.  Addition  of  acid  reprecipitates  the 
sulphides. 

2.  Add   1  or  2  c.c.  of  silver  nitrate  solution  to  about  5   c.c.  of  the 
arsenousacid  solution  ;  no  precipitate  results.   Now  pour  carefully  upon 
the  surface  of  the  mixture  a  little  very  dilute  ammonia  water  ;  a  yellow 
precipitate  of  silver  arsenite  (Plate  V.,  3)  is  formed  at  the  line  of  con- 
tact of  the  two  liquids,  which  may  be  increased  by  cautiously  mixing 
the  liquids.     The  precipitate  is  soluble  in  excess  of  ammonia  or  in 
nitric  acid.     When  solution  of  an  arsenite  instead  of  free  arsenous 
acid  is  used,  silver  nitrate  gives  a  precipitate  at  once,  without  addition 
of  ammonia  water  : 

H3As03  +  3AgN03  +  3NH4OH  ==  Ag3AsO3  +  3NH4NO8  +  3H2O. 

Na3AsO3  +  3AgNO3    ==  Ag3AsO3  +  3NaNO3. 

Dissolve  the  precipitate  in  a  slight  excess  of  ammonia  water,  add  a 
few  drops  of  caustic  soda,  and  apply  heat  ;  a  mirror  of  metallic  silver 
is  formed,  due  to  the  reducing  action  of  the  arsenite,  which  becomes 
arsenate. 

When  silver  nitrate  is  added  to  the  sodium  arsenate  solution  (about 
3  c.c.),  a  reddish-brown  precipitate  of  silver  arsenate  is  formed,  which 
is  soluble  in  ammonia  water  or  nitric  acid  (Plate  V.,  4)  : 

Na2HAsO4  4-  3AgNO3  =  Ag3AsO4  +  2NaNO3  +  HNO3. 

3.  Add  2  or  3  drops  (avoid  excess)  of  copper  sulphate  solution  to 
about  5  c.c.  of  the  arsenous  acid,  and  overlay  the  mixture  with  very 
dilute  ammonia  water  as  in  test  2   (if  an  arsenite  is  used,   ammonia 
water  is  unnecessary)  ;  a  green  precipitate  of  copper  arsenite,  Scheele's 
green,  CuHAsO3,  is  produced  (Plate  V.,  2).     Add  some  caustic  alkali 
solution  to  the  precipitate  and  boil  ;  red  cuprous  oxide  is  formed,  due  to 
reduction  by  the  arsenite,  which  becomes  arsenate.     (Schweinfurt  green, 
copper  aceto-arsenite,  3Cu(AsO2)2.Cu(C2H3O2)2,  is  obtained  by  adding 
solution  of  copper  acetate  to  a  boiling  solution  of  an  arsenite.       This 
and  Scheele's  green  are  often  called  Paris  green.) 

When  copper  sulphate  solution  is  added  to  the  sodium  arsenate  solu- 
tion, a  greenish-blue  precipitate  of  copper  arsenate,  CuHAsO4,  is 


ARSENIC    ANTIMONY,    TIN. 


PLATE  V 


Arscnous  sulphide,  precipitated  fr< 
arsenous  solutions  by  hydrogen  sulphii 


Cupric  arsenite,  precipitated  fr< 
arsenous  solutions  by  cupric-ammonh 
sulphate. 


Silver    arsenite,    precipitated     frc 
arsenous  solutions  by  silver  nitrate. 


Silver     arsenate,    precipitated    fro 
arsenic  solutions  by  silver  nitrate. 


Antimonous  sulphide,  precipital 
from  solutions  of  antimony  by  hydrog 
sulphide. 


Native  or  crystallized  antimono 
sulphide. 


Stannous  sulphide,  precipitated  frc 
stannous  solutions  by  hydrogen  sulphic 


Stannic    sulphide,   precipitated   fn 
stannic  solutions  by  hydrogen  sulphide. 


Affoen  &  Co  LiUi.  Baltimore, . 


ARSENIC.  353 

formed.      All  these  precipitates  are  soluble  in  ammonia  water  and  in 
acids. 

4.  Add  to  a  little  of  the  arsenate  solution,  a  clear  mixture  of  mag- 
nesium sulphate,  ammonium  chloride  and  ammonia  water,  and  shake  ; 
a   white  precipitate   of  ammonium   magnesium  arsenate  is  formed, 
NH4MgAsO4  (see  test  1  under  phosphoric  acid). 

Magnesium  arsenite  is  insoluble  in  water,  but  soluble  in  ammonia 
water  and  in  ammonium  chloride  solution. 

5.  Add  to  a  few  drops  of  the  arsenate  solution,  excess  of  ammonium 
molybdate  solution  (about  5  c.c.)  and  warm  gently  ;  a*  yellow  precipi- 
tate of  ammonium  arseno-molybdate  is  formed,  similar  in  all  respects 
to  the  corresponding  phosphorus  compound.     (Arsenic  is  the  only 
other  element  which  behaves  like  phosphorus  toward  the  molybdate 
reagent.)     Arsenites  give  no  precipitate  with  the  reagent. 

6.  Heat  any  dry  arsenic  compound,  after  being  mixed  with  some 
charcoal  and  dry  potassium  carbonate  in  a  very  narrow  test-tube  (or, 
better,  in  a  drawn-out  glass  tube  having  a  small  bulb  on  the  end)  :  the 
arsenic  compound  is  decomposed  and  the  element  arsenic  deposited 
as  a  metallic  ring  in  the  upper  part  of  the  contraction.     (Fig.  44.) 

FIG.  44. 


7.  Heat  arsenous  or  arsenic  oxide  upon  a  piece  of  charcoal  by 
means   of  a   blow-pipe  :  a   characteristic   odor   of  garlic  is  percep- 
tible. 

8.  Reimch's  test.     A  thin  piece  of  copper,  having  a  bright  metallic 
surface,  placed  in  a  solution  of  arsenic,  strongly  acidified  with  con- 
centrated hydrochloric  acid,  becomes,  upon  heating  the  solution,  coated 

23 


354  METALS  AND   THEIR  COMBINATIONS. 

with  a  dark  steel-gray  deposit  of  arsenic,  which  can  be  vaporized  by 
application  of  heat.     Antimony  also  responds  to  this  test. 

9.  Bettendorf's  test,  U.  S.  P.  Add  to  any  arsenic  compound,  dis- 
FIG  45  solved  in  concentrated  hydrochloric  acid,  an  equal  vol- 
ume of  freshly  prepared  saturated  solution  of  stannous 
chloride  in  concentrated  hydrochloric  acid,  and  heat  in 
boiling  water  for  15  minutes  ;  a  brown  color  or  precipi- 
tate is  formed,  due  to  separation  of  the  arsenic.  Anti- 
mony does  not  respond  to  this  test. 

10.  Gutzeit's  test.  Place  a  small  piece  (about  1 
gramme)  of  pure  zinc  in  a  test-tube,  add  about  5  c.c. 
of  dilute  (5  per  cent.)  sulphuric  acid  and  a  few  drops 
of  any  arsenic  solution,  which  should  not  be  alkaline. 
Fasten  over  the  mouth  of  the  test-tube  a  cap  made  of 
three  thicknesses  of  pure  filter-paper,  and  moisten  the 
upper  paper  with  a  drop  of  a  saturated  solution  of 
silver  nitrate  in  water  acidulated  with  about  1  per 
cent,  of  nitric  acid.  (Fig.  45.)  Place  the  tube  in  a 
box  so  as  to  exclude  all  light,  and  examine  the  paper 
cap  after  awhile.  Upon  it  will  appear  a  bright-yellow 
stain,  rapidly  if  the  quantity  of  arsenic  be  considerable, 
slowly  if  it  be  small.  Upon  moistening  the  yellow 
stain  with  water  the  color  changes  to  brown  or  black. 
The  action  of  hydrogen  arsenide  upon  silver  nitrate  in 
the  absence  of  water  takes  place  with  the  formation  of  a  yellow  com- 
pound, thus : 

AsH3  +  6AgNO3  =  3HNO,  -f  Ag3As.(AgNO3)3. 

In  the  presence  of  water  metallic  silver  is  separated,  showing  a 
black  or  brown  color : 

AsH3  +  6AgN03  +  3H20  =--  6HNO,  +  H3AsO3  +  6Ag. 

Compounds  of  antimony  treated  in  the  above  manner  produce  a 
dark  spot  upon  the  paper,  but  cause  no  previous  yellow  color. 

Modified  Gutzeit's  test,  U.  S.  P.  This  is  employed  in  nearly  all 
instances  in  the  U.  S.  P.  where  traces  of  arsenic  are  tested  for  in  official 
products.  It  cannot  be  used  in  the  case  of  bismuth  or  antimony 
compounds,  for  which  Bettendorf's  test  is  employed.  The  test  is 
carried  out  as  follows  : 

All  the  tests  for  arsenic  bearing  proper  names  are  intended  to  be 
applied  for  the  detection  of  minute  quantities  of  arsenic.  If  arsenic 


ARSENIC.  355 

compounds  themselves  are  used,  only  very  dilute  solutions  should  be 
tested,  in  order  to  appreciate  the  delicacy  of  the  tests.  The  arsenic 
should  be  in  the  form  of  an  arsenows  compound  for  the  above  test,  as 
in  this  condition  it  is  more  readily  reduced  to  arsine.  This  is  insured 
by  adding  to  5  c.c.  of  a  10  per  cent,  aqueous  solution  of  the  chemical 
to  be  tested  (in  some  instances  special  previous  treatment  is  neces- 
sary, which  may  be  seen  in  the  U.  S.  P.)  1  c.c.  of  a  mixture  of  equal 
volumes  of  concentrated  sulphuric  acid  and  water,  and  10  c.c.  of 
fresh  saturated  solution  of  sulphur  dioxide.  The  liquid  is  evaporated 
over  boiling  water  until  it  is  free  from  sulphur  dioxide  and  has  been 
reduced  to  5  c.c.  in  volume.  It  is  then  introduced  into  a  75  c.c.  flask 
containing  2  or  3  grammes  of  granular  zinc  and  20  c.c.  of  8  per  cent, 
hydrochloric  acid,  a  small  wad  of  clean  dry  gauze  is  inserted  into  the 
lower  end  of  the  neck  of  the  flask,  followed  by  a  wad  moistened  with 
lead  acetate  solution.  The  mouth  of  the  flask  is  then  covered  by 
folding  over  it  a  filter-paper,  the  center  of  which  has  previously  been 
three  times  successively  wet  with  a  saturated  alcoholic  solution  of 
mercuric  chloride  and  dried.  After  one-half  to  one  hour,  the  paper  cap 
is  examined  for  a  yellow  stain,  which  indicates  arsenic.  The  presence 
of  arsenic  much  in  excess  of  the  permissible  limit  of  the  U.  S.  P. 
(1  in  100,000)  is  shown  by  a  distinct  yellow  to  orange  spot.  All  the 
reagents  used  must  be  free  from  arsenic,  which  is  determined  by 
making  a  blank  test,  omitting  the  chemical  to  be  tested.  The  stu- 
dent should  carry  out  the  test  on  2  or  3  c.c.  of  a  -§\-$  per  cent,  solu- 
tion of  arsenic  trioxide,  which  need  not  be  submitted  to  the  reduc- 
tion with  sulphur  dioxide.  Antimony  gives  a  dark  coloration. 

11.  Fleitmann's  test.     This  is  similar  to  the  Gutzeit's  test,  the 
chief  difference  being  that  hydrogen  is  evolved  in  alkaline  solution, 
which  has  the  advantage  that  the  presence  of  antimony  does  not 
interfere,  because  this  metal  does  not  form  antimonetted  hydrogen  in 
alkaline  solutions. 

Place  about  1  gramme  of  pure  zinc  in  a  test-tube,  add  about  5  c.c. 
of  potassium  hydroxide  solution  and  a  few  drops  of  the  arsenic  solu- 
tion, which  should  not  be  acid.  Provide  paper  cap  as  described  in 
Gutzeit's  test,  and  set  the  test-tube  in  a  box  containing  sand  heated 
to  about  90°  C.  (194°  F.).  A  brown  or  black  stain  of  metallic  silver 
will  appear  upon  the  paper. 

12.  Marsh's  test.     While  this  test  is  not  used  now  for  qualitative 
determinations  as  much  as  formerly,  it  is  of  great  value  because  it 
may  serve  for  collecting  the  total  amount  of  arsenic  present  in  a 
specimen,  thus  permitting  quantitative  estimation.     The  apparatus 


356  METALS  AND   THEIR   COMBINATIONS. 

(Fig.  46)  used  for  performing  this  test  consists  of  a  glass  vessel  (flask 
or  WoulPs  bottle)  provided  with  a  funnel-tube  and  delivery-tube 
(bent  at  right  angles),  which  is  connected  with  a  wider  tube,  filled 
with  pieces  of  calcium  chloride  or  plugs  of  asbestos;  this  drying-tube 
is  again  connected  with  a  piece  of  hard  glass  tube,  about  one  foot 
long,  having  a  diameter  of  J  inch,  drawn  out  at  intervals  of  about 
3  inches,  so  as  to  reduce  its  diameter  to  J  inch.  Hydrogen  is  gener- 
ated in  the  flask  by  the  action  of  sulphuric  acid  on  zinc,  and  ex- 
amined for  its  purity  by  heating  the  glass  tube  to  redness  at  one  of 
its  wide  parts  for  at  least  30  minutes ;  if  no  trace  of  a  metallic  mirror 
is  formed  at  the  constriction  beyond  the  heated  point,  the  gas  and  the 
substances  used  for  its  generation  may  be  pronounced  free  from 
arsenic.  (Both  zinc  and  sulphuric  acid  often  contain  arsenic.) 

FIG.  46. 


lllillllillllllllMIMII1!linil1lll1tl)l1limnilinnitiiMiiiiitiiiiimni» 

uliliililiilllillllillliilllllllllM 

Marsh's  apparatus  for  detection  of  arsenic. 

After  having  thus  demonstrated  the  purity  of  the  hydrogen,  the 

uspected  liquid,  which  must  contain  the  arsenic  either  as  oxide  or 

chlonde  (not  as  sulphide),  is  poured  into  the  flask  through  the  funnel- 

If  arsenic  is  present  in  not  too  small  quantities,  the  gas  ignited 

the  end  of  the  glass  tube  shows  a  flame  decidedly  different  from 

tiiut  ot  Durnino*  hvdroo'pn      TM      fl          K  i 

appt^whichfs'ml^  "  f  °Pf  ^^^it  a  wSdteud 

ovpr  tli    fl  °r     SS         se  >  a  c°ld  test-tube  held  inverted 

lame  will  be  covered  upon  its  walls  with  a  white  deposit  of 
ctahedral  crystals  of  n,senous  oxide.  a  piece  rf  coIdPporce. 

coated  with  a  brown  stain  (arsenic 
above  in  connection  with 


ARSENIC. 


357 


> 


The  glass  tube  heated,  as  above  mentioned,  at  one  of  its  wide  parts, 
will  show  a  bluish-black  metallic  mirror  at  the  constriction  beyond. 

If  quantitative  determination  is  desired,  the  glass  tube  is  heated  in  two 
places  so  as  to  cause  all  hydrogen  arsenide  to  be  decomposed.  To  collect, 
however,  the  arsenic  from  any  gas  that  might  escape,  the  end  of  the  tube 
is  inverted  and  placed  into  solution  of  nitrate  of  silver,  which  is  decomposed 
by  the  hydrogen  arsenide,  silver  and  arsenous  acid  being  formed.  The  arsenic 
solution  should  be  introduced  into  the  hydrogen  generator  in  small  portions, 
so  as  not  to  produce  more  hydrogen  arsenide  at  a  time  than  can  be  decom- 
posed by  the  method  given. 

The  only  element  which,  under  the  same  conditions,  forms  spots  and  mirrors 
similar  to  arsenic,  is  antimony  ;  there  are,  however,  sufficiently  reliable  tests 
to  distinguish  arsenic  spots  from  those  of  antimony. 

Arsenic  spots  treated  with  solution  of  hypochlorites  (solution  of  bleaching- 
powder)  dissolve  readily  ;  antimony  spots  are  not  affected.  When  nitric  acid 
is  added  to  an  arsenic  spot  and  evaporated  to  dryness  and  the  spot  moistened 
with  a  drop  of  silver  nitrate,  it  turns  brick-red  ;  antimony  spots  treated  in  like 
manner  remain  white.  Arsenic  spots  dissolved  in  ammonium  sulphide  and 
evaporated  to  dryness  show  a  bright-yellow,  antimony  spots  an  orange-red, 
residue.  Fig.  47  represents  a  simpler  form  of  Marsh's  appara- 
tus, which  generally  will  answer  for  students'  tests. 

Preparatory  treatment  of  organic  matter  for  arsenic 
analysis.  If  organic  matter  is  to  be  examined  for  arsenic 
(or  for  any  other  metallic  poison),  it  ought  to  be  treated  as 
follows  :  The  substance,  if  not  liquid,  is  cut  into  pieces,  well 
mashed  and  mixed  with  water;  the  liquid  or  semi-liquid  sub- 
stance is  heated  in  a  porcelain  dish  over  a  steam  bath  with 
hydrochloric  acid  and  potassium  chlorate  until  the  mass  has  a 
uniform  light  yellow  color  and  has  no  longer  the  odor  of 
chlorine.  By  this  operation  all  poisonous  metals  (lead  and 
silver  excepted,  because  insoluble  silver  chloride  and  possibly 
insoluble  lead  sulphate  are  formed)  are  rendered  soluble  evgn 
when  present  as  sulphides,  and  may  now  be  separated  by  filtra- 
tion from  the  remaining  solid  matter  The  clear  solution  is 
heated  and  treated  with  hydrogen  sulphide  gas  for  several 
hours,  when  arsenic  and  all  metals  of  the  arsenic  and  lead 
groups  are  precipitated  as  sulphides,  a  little  organic  matter 
also  being  precipitated  generally. 

The  precipitate  is  collected  upon  a  small  filter  and  treated  with  warm  ammo- 
nium sulphide,  which  dissolves  the  sulphides  of  arsenic  and  antimony,  leaving 
behind  the  sulphides  of  the  lead  group,  which  may  be  dissolved  in  nitric,  or,  if 
mercury  be  present,  in  nitro-hydrochloric  acid,  and  the  solution  tested  by  the 
methods  mentioned  for  the  respective  metals.  The  ammonium  sulphide  solu- 
tion is  evaporated  to  dryness,  this  residue  mixed  with  nitrate  and  carbonate  of 
sodium,  and  the  mixture  fused  in  a  small  porcelain  crucible.  By  the  oxidizing 
action  of  the  nitrate,  both  sulphides  are  converted  into  the  higher  oxides, 
arsenic  forming  sodium  arsenate,  antimony  forming  antimonic  oxide.  By 
treating  the  mass  with  warm  water,  sodium  arsenate  is  dissolved  and  may  be 


358  METALS  AND   THEIR  COMBINATIONS, 

filtered  off,  while  antimonic  oxide  remains  undissolved,  and  may  be  dissolved  in 
hydrochloric  acid.  Both  solutions  may  now  be  used  for  making  the  respective 
tests  for  arsenic  or  antimony. 

Comments.  Tests  1,  6,  and  3  are  sufficient  to  identify  arsenic  compounds. 
Test  3  will  detect  an  arsenite  in  presence  of  an  arsenate,  and  tests  4  and  5  an 
arsenate  in  presence  of  an  arsenite.  Test  10,  especially  in  the  modified  form, 
and  Test  12  are  most  often  used  to  detect  traces  of  arsenic. 

Alkali  arsenites  are  soluble  in  water;  all  others  are  either  insoluble  or  diffi- 
cultly soluble  in  water.  Alkali  arsenates  and  acid  arsenates  of  the  alkaline 
earths  are  soluble  in  water.  All  the  salts  are  soluble  in  mineral  acids. 

Arsenous  acid  dissociates  very  slightly,  and  is  therefore  a  weak  acid.  Its 
soluble  salts  are  hydrolyzed  to  a  considerable  extent,  and  show  an  alkaline 
reaction.  Boiling  a  solution  of  arsenous  acid  or  its  salts  in  hydrochloric  acid 
results  in  a  loss  of  arsenic  by  volatilization  as  arsenous  chloride.  Solutions 
of  arsenic  acid  or  its  salts  suffer  no  loss  of  arsenic  in  this  manner. 

Arsenic  acid  dissociates  very  much  like  phosphoric  acid,  but  to  a  little  less 
extent  than  the  latter  in  solutions  of  equal  concentration.  Even  in  high  dilu- 
tion the  dissociation  is  mainly  thus : 

H3AsO4  ^  H-  -f  H2AsO4'. 
Further  dissociation  into  HAsO/'  and  AsO/"  ions  is  very  slight. 

Antidotes.  Moist,  recently  prepared  ferric  hydroxide  or  dialyzed  iron  are 
the  best  antidotes.  Vomiting  should  be  induced  by  tickling  the  fauces  or  by 
administering  zinc  sulphate,  but  not  tarter  emetic. 


33.  ANTIMONY— TIN-GOLD— PLATINUM— MOLYBDENUM. 

Antimony,  Sb  :  =  119.3  (Stibium).  This  metal  is  found  in  nature 
chiefly  as  the  trisulphide,  Sb2S3,  an  ore  which  is  known  as  black  anti- 
mony, crude  antimony,  or  stibnite. 

The  metal  is  obtained  from  the  sulphide  by  roasting,  when  it  is 
converted  into  oxide,  which  is  reduced  by  charcoal.  Antimony  is  a 
brittle,  bluish-white  metal,  having  a  crystalline  structure ;  it  fuses  at 

QUESTIONS.— Which  metals  belong  to  the  arsenic  group ;  what  are  their 
characteristics?    Which  non-metallic  elements  does  arsenic  resemble?    Men- 
tion  some  of  the  compounds  showing  this  analogy.     How  is  arsenic  obtained 
in  the  free  state;  what  are  its  physical  and  chemical  properties;  how  does 
leat  act  upon  it?     What  is  white  arsenic?    State  its  composition,  mode  of 
manufacture,  appearance,  solubility,  and  other  properties.     Which  three  solu- 
ns,  containing  arsenic,  are  official,  and  what  is  their  composition  ?    How  is 
3  acid  obtained  from  arsenous  oxide,  and  which  arsenate  is  official? 
composition  and  properties  of  arsenetted  hydrogen,  and  explain  its  for- 
mation.   What  use  is  made  of  it  in  testing  for  arsenic  ?    State  the  composition 
realgar,  orpiment,  Scheele's  green,  and  Schweinfurth  green.    Give  a  detailed 
tion  of  the  process  by  which  arsenic  can  be  detected  in  organic  matter. 
Describe  in  detail  the  principal  tests  for  arsenic. 


ANTIMONY.  359 

450°  C.  (842°  F.),  and  may  at  a  higher  temperature  be  distilled  without 
change,  provided  air  is  excluded  ;  heated  in  air  it  burns  brilliantly. 

Antimony  is  used  in  a  number  of  important  alloys,  for  instance,  in 
type-metal,  an  alloy  of  lead,  tin,  and  antimony. 

The  best  solvent  for  antimony  is  hydrochloric  acid,  containing  a 
little  nitric  acid,  whereby  antimonous  or  antimonic  chloride  is 
formed.  Nitric  acid  converts  it  into  antimonous  or  antimonic  oxide, 
which  are  almost  insoluble  in  the  liquid. 

Three  oxides  of  antimony  are  known,  namely,  trioxide,  Sb2O3, 
pentoxide,  Sb2O5,  and  tetroxide,  Sb2O4.  Antimony  differs  from 
arsenic  in  that  the  trioxide  is  more  basic  than  acidic,  forming  salts 
with  mineral  and  organic  acids.  The  salts  with  mineral  acids,  how- 
ever, are  decomposed  by  water,  and  require  the  presence  of  free  acid 
for  solution.  Antimony  pentoxide  is  exclusively  acidic  in  character, 
forming  met-antimonates  and  pyro-antimonates  with  caustic  alkalies. 
The  tetroxide  is  neither  basic  nor  acidic.  It  is  formed  when  either 
of  the  other  oxides  is  heated  in  air  to  a  dull  redness  for  a  long  time. 

The  compounds  of  antimony  commonly  met  with  are  the  chloride, 
sulphide,  and  double  tartrate  (tartar  emetic). 

Antimony  trisulphide,  Sb2S3  (Antimonous  sulphide).  The  above- 
mentioned  native  sulphide,  the  black  antimony,  is  found  generally 
associated  with  other  ores  or  minerals,  from  which  it  is  freed  by  heat- 
ing the  masses,  when  the  antimony  sulphide  fuses  and  is  made  to  run 
off  into  suitable  vessels  for  cooling.  Thus  obtained  it  forms  steel- 
gray  masses  of  a  metallic  lustre,  and  a  striated,  crystalline  fracture, 
forming  a  grayish-black,  lustreless  powder,  which  is  insoluble  in 
water,  but  soluble  in  hydrochloric  acid  with  liberation  of  hydrogen 
sulphide. 

Antimonous  sulphide  found  in  nature  is  crystallized  and  steel-gray 
(Plate  V.,  6),  but  it  may  be  obtained  also  in  an  amorphous  condition 
as  an  orange-red  (Plate  V.,  5)  powder  by  passing  hydrogen  sulphide 
through  an  antimouous  solution.  By  heating  the  orange-red  sul- 
phide, it  is  converted  into  the  black  variety. 

The  sulphides  and  oxides  of  antimony,  like  those  of  arsenic,  combine  with 
many  metallic  sulphides  or  oxides  to  form  sulpho-salts  or  oxy-salts.  Thus  the 
sodium  sulph-antimonite,  Na3SbS3,  and  the  sodium  antimonite,  NaSb02,  are 
formed  when  antimonous  sulphide  is  boiled  with  sodium  hydroxide. 

Sb2S3  +  4NaOII  =  Na3SbS3  +  NaSbO,  +  2H2O. 

By  the  addition  of  sulphuric  acid,  both  salts  are  decomposed,  sodium  sulphate 
is  formed,  and  antimonous  sulphide  is  precipitated : 

Na3SbS3  +  NaSbO2  +  2H2SO4  =  Sb2S3  +  2Na2SO4  +  2H2O. 


360  METALS  AND   THEIR   COMBINATIONS. 

While  the  above  is  the  principal  reaction,  there  is  formed  also  some  anti- 
mony oxide. 

Experiment  48.  Intimately  mix  about  0.5  gramme  of  finely  powdered  black 
antimony  sulphide  with  some  sodium  carbonate  and  potassium  cyanide. 
Heat  this  mixture  with  a  blowpipe  flame  on  charcoal  till  it  fuses  thoroughly 
and  a  bead  of  metallic  antimony  is  obtained.  Drop  the  molten  antimony 
from  the  height  of  about  a  foot  upon  a  sheet  of  paper  and  notice  that 
characteristic  grayish-white  streaks  are  formed,  radiating  in  all  directions. 
Test  the  crust  (left  on  the  charcoal)  on  a  silver  coin  for  sulphur.  Examine 
another  bead  of  antimony  for  cplor,  hardness,  malleability,  etc. ;  then  try  its 
solubility  in  acids  in  the  order  of  hydrochloric,  dilute  sulphuric,  nitric,  and 
nitre-hydrochloric  acids. 

Antimony  pentasulphide,  Sb2S5  (Golden  sulphur et  of  antimony). 
A  red  powder,  which,  like  antimonotis  sulphide,  forms  sulpho-salts. 
It  may  be  obtained  by  precipitation  of  acid  solutions  of  antimonic 
acid  by  hydrogen  sulphide. 

Antimonous  chloride,  SbCl3  (Antimony  terchloride,  Butter  of  anti- 
mony). Obtained  by  boiling  the  native  sulphide  with  hydrochloric 
acid: 

Sb2S3  4-  6HC1  =  3H2S  4-  2SbCl3. 

The  clear  solution  is  evaporated  and  the  remaining  chloride  dis- 
tilled, when  it  is  obtained  as  a  white,  crystalline,  semi-transparent 
mass. 

By  passing  chlorine  over  antimonous  chloride  it  is  converted  into 
antimonic  chloride,  SbCl5,  which  is  a  fuming  liquid. 

Experiment  49.  Boil  about  2  grammes  of  black  antimony  with  10  c.  c.  of 
hydrochloric  acid  until  most  of  the  sulphide  is  dissolved.  Set  aside  for  sub- 
sidence, pour  off  the  clear  solution  of  antimonous  chloride,  evaporate  to  about 
half  its  volume  and  use  solution  for  next  experiment. 

Antimonous  oxide  (Antimony  trioxide).  When  antimonous  chlo- 
ride is  added  to  water  decomposition  takes  place  similar  to  the  one 
which  normal  bismuth  salts  undergo  by  the  action  of  water,  viz.,  a 
white  precipitate  of  oxy-chloride  of  antimony  (antimonyl  chloride), 
BbOCl,  is  formed,  which,  however,  is  mixed  with  antimonous  oxide, 
as  the  following  two  reactions  take  place : 

SbCl3  +  H2O  =  SbOCl  4-  2HC1. 
2SbCl3  4-  3H20  =  Sb203  4-  6HC1. 

The  relative  proportions  of  the  two  constituents  depend  on  the 
mode  of  manipulating  and  on  the  quantity  of  water  used. 

The  white  precipitate  was  formerly  known  as  powder  of  Algaroth. 


ANTIMONY.  361 

It  is  completely  converted  into  oxide  by  treating  it  with  sodium  car- 
bonate : 

2SbOCl  +  Na2CO3  =  Sb,O3  -f  2NaCl  +  CO2. 

The  precipitate  when  washed  and  dried  is  a  heavy,  grayish-white, 
tasteless  powder,  insoluble  in  water,  soluble  in  hydrochloric  acid,  and 
also  in  a  warm  solution  of  tartaric  acid.  Antimonous  oxide,  while 
yet  moist,  dissolves  readily  in  potassium  acid  tartrate,  forming  the 
double  tartrate  of  potassium  and  antimony,  or  tartar  emetic,  which  salt 
will  be  more  fully  considered  hereafter. 

Experiment  50.  Pour  the  antimonous  chloride  solution  (obtained  by  Ex- 
periment 49),  which  should  have  been  boiled  sufficiently  to  expel  all  hydrogen 
sulphide,  into  100  c.c.  of  water,  wash  by  decantation  the  white  precipitate  of 
oxychloride  thus  obtained,  and  add  to  it  an  aqueous  solution  of  about  1  gramme 
of  sodium  carbonate.  After  effervescence  ceases,  collect  the  precipitate  on  a 
filter,  wash  well  and  treat  some  of  the  precipitate,  while  yet  moist,  with  a  solu- 
tion of  potassium  acid  tartrate,  which  dissolves  it  readily,  forming  tartar  emetic. 
(For  the  latter  compound  see  index.) 

Antidotes.  Poisonous  doses  of  any  preparation  of  antimony  are  generally 
quickly  followed  by  vomiting  :  if  this,  however,  have  not  occurred,  the  stomach- 
pump  must  be  applied.  Tannic  acid  in  any  form,  or  recently  precipitated  ferric 
hydroxide,  should  be  administered. 

Tests  for  antimony. 

(Use  a  solution  of  antimony  chloride  prepared  as  in  Experiment  49,  and  diluted  to 
about  30  c.c.  by  adding,  first,  2  or  3  c.c.  of  dilute  hydrochloric  acid,  and  then  water 
cautiously.  Also  a  5  percent,  solution  of  tartar  emetic,  K(SbO)C4H4O6,  in  water. 
Note  that  the  latter  dissolves  easily  and  without  decomposition.) 

1.  Add  hydrogen  sulphide   to  some  of  the  solution  of  antimony 
chloride  :  an  orange-red  precipitate  of  antimonons  sulphide  (Sb2S3)  is 
produced  (Plate  V.,  5). 

Hydrogen  sulphide  produces  the  same  precipitate  in  the  solution  of 
tartar  emetic. 

2.  Add  yellow  ammonium  sulphide  to  the  precipitated  sulphide  of 
antimony  :  this  is  dissolved  and  may  be  reprecipitated  by  neutralizing 
with  an  acid.     The  same  results  are  obtained  with  caustic  alkalies. 

3.  Produce    a  concentrated    solution  of  antimonous    chloride   by 
evaporation  or  by  dissolving  the  sulphide  in  hydrochloric  acid,  and 
pour  it  into  water  :  a  white  precipitate  of  oxychloride  is  formed.   (See 
explanation  above.) 

Add  a  few  drops  of  dilute  hydrochloric  acid  to  some  of  the  solution 
of  tartar  emetic  :  a  white  precipitate  of  oxychloride  is  also  formed.  In 
analysis,  this  might  be  mistaken  for  a  chloride  of  silver,  lead,  or  mer- 
cury, but  it  differs  from  the  latter  by  being  soluble  in  excess  of  the  acid. 


362  METALS  AND  THEIR  COMBINATIONS. 

4.  Add  sodium  hydroxide,  ammonium  hydroxide,  or  sodium  car- 
bonate to  the  antimony  chloride  solution  :  in  either  case  white  anti- 
moDOus  hydroxide,  Sb(OH)3,  is  produced,  which  is  soluble  in   excess 
of  sodium  hydroxide. 

The  same  reagents  added  to  the  solution  of  tartar  emetic  produce 
scarcely  any  precipitate,  due  to  the  solvent  effect  of  the  organic  (tartaric) 
acid. 

5.  Boil  a  piece  of  bright  metallic  copper  in  the  solution  of  anti- 
monous  chloride  :  a  black  deposit  of  antimony  is  formed  upon  the  cop- 
per.   By  heating  the  latter  in  a  narrow  test-tube,  the  antimony  is  volatil- 
ized and  deposited  as  a  white  incrustation  of  antimonous  oxide  upon 
the  glass. 

6.  Use  Gutzeit's  or  Marsh's  test  as  described  under  tests  for  arsenic. 

Tin,  Sn  =  118.8  (8tannum).  This  metal  is  found  in  nature  chiefly 
as  stannic  oxide  or  tin-stone,  SnO2,  from  which  the  metal  is  easily 
obtained  by  heating  with  coal : 

Sn02  +  20  =  Sn  +  2CO. 

Tin  is  an  almost  silver-white,  very  malleable  metal,  fusing  at  the 
comparatively  low  temperature  of  228°  C.  (440°  F.).  It  is  used  in 
many  alloys,  and  chiefly  in  the  manufacture  of  tin-plate,  which  is 
sheet-iron  covered  with  a  thin  layer  of  tin. 

Tin  is  bivalent  in  some  compounds,  quadrivalent  in  others.  These 
combinations  are  distinguished  as  stanuous  and  stannic  compounds. 

Stannous  hydroxide,  Sn(OH)2,  is  not  known.  When  a  solution  of 
sodium  hydroxide  or  carbonate  is  added  to  a  solution  of  stannous 
chloride,  a  precipitate,  H2Sn2O3,  is  formed,  which  is  derived  from 
Sn(OH)2.  When  it  is  heated  in  an  atmosphere  of  carbon  dioxide, 
black  stannous  oxide,  SnO,  is  formed,  which  ignites  when  heated  in 
air,  giving  stannic  oxide. 

Stannic  hydroxide  (Stannic  acid),  H2SnO3,  is  formed  when  a  solu- 
tion of  stannic  chloride  is  boiled  : 

SnCl4    +    3H20    =    H2Sn03    +    4HC1. 

It  is  also  formed  when  sodium  hydroxide  or  carbonate  is  added  to  a 
solution  of  stannic  chloride,  or  when  just  enough  of  an  acid  is  added 
to  a  solution  of  a  stannate  to  effect  decomposition  : 

Na2Sn03    +    2HC1     =     2NaCl    +     H2Sn03. 

It  is  a  white  substance  insoluble  in  water,  but  easily  soluble  in 
hydrochloric,  nitric,  or  sulphuric  acid,  forming  the  corresponding  salt, 
and  in  caustic  alkalies,  forming  stannates. 


TIN.  363 

Metastannic  acid  is  formed  when  tin  is  treated  with  concentrated 
nitric  acid.  It  is  a  white  powder  insoluble  in  water  and  acids,  hut 
seems  to  have  the  same  composition  as  stannic  acid.  It  forms  salts 
with  alkalies  which  are  entirely  different  in  properties  and  composition 
from  the  stannates,  and  are  known  as  meta  stannates.  Two  sodium  salts 
are  known,  Na.^Sn^Oj!  and  Na2Sn9O19.  When  the  acid  is  heated, 
stannic  oxide,  SnO2,  is  formed. 

Stannous  chloride,   SnCl2  (Protochloride  of  tin).     Obtained  by 
dissolving  tin  in  hydrochloric  acid  by  the  aid  of  heat : 
Sn  +  2HC1  =  SnCl2  +  2H. 

Sufficiently  evaporated,  the  solution  yields  crystals  of  the  composi- 
tion SnCl2.2H2O.  Stannous  chloride  is  a  strong  deoxidizing  agent, 
frequently  used  as  a  reagent  for  arsenic,  mercury,  and  gold,  which 
metals  are  precipitated  from  their  solutions  in  the  metallic  state.  It 
is  used  also  in  calico  printing. 

Stannic  chloride,  SnCl4  (Perchloride  of  tin).  Stannous  chloride 
may  be  converted  into  stannic  chloride  either  by  passing  chlorine 
through  its  solution  or  by  heating  with  hydrochloric  and  nitric  acids. 

Tests  for  tin. 
(Stannous  chloride,  SnCl.2,  and  stannic  chloride,  SnCl4,  may  be  used.) 

1 .  Add  hydrogen  sulphide  to  solution  of  a  stannous  salt :  brown 
stannous  sulphide  is  precipitated  (Plate  V.,  7)  : 

SnCl2     +   -H2S  2HC1     +     SnS. 

The  precipitate  is  soluble  in  yellow  ammonium  sulphide. 

2.  Add  hydrogen  sulphide  to  a  solution  of  a   stannic  salt :  yellow 
stannic  sulphide  is  precipitated  (Plate  V.,  8) : 

SnCl4  +  4H2S  =  4HC1  -f  SnS2. 

The  precipitate  is  soluble  in  ammonium  sulphide. 

3.  Sodium  or  potassium  hydroxide  added  to  a  stannous  salt  pro- 
duces a  white  precipitate  of  stannous  hydroxide,  Sn(OH)2.    The  same 
reagents  added  to  a  stannic  salt  produce  white  stannic  acid,  H2SnO3. 
Both  precipitates  are  soluble  in  excess  of  the  alkali,  forming  stannite, 
Na2SnO2,  and  stannate,  Na2SnO3. 

Gold,  Au  =  195.7  (Aurum).  Gold  occurs  in  nature  chiefly  in  the 
free  state,  generally  associated  with  silver,  copper,  and  possibly  with 


364  METALS  AND  THP:1R  COMBINATIONS. 

other  metals,  sometimes  also  in  combination  with  selenium  and  tellu- 
rium. This  impure  gold  is  separated  from  most  of  the  adhering 
sand  and  rock  by  a  mechanical  process  of  washing,  in  which  advan- 
tage is  taken  of  the  high  specific  gravity  of  the  metallic  masses.  The 
remaining  mixture  of  heavy  material  is  treated  with  mercury,  which 
dissolves  gold  and  silver,  leaving  behind  most  other  impurities.  The 
gold  amalgam  is  placed  in  a  retort  and  heated,  when  the  mercury 
distils  over,  while  the  gold  is  left  behind. 

From  ores  containing  but  little  gold  the  metal  is  now  extracted 
largely  by  treating  the  finely  powdered  material  with  a  solution  of 
potassium  cyanide,  which  forms  a  soluble  double  cyanide  of  gold  and 
potassium,  AuK(CN)2.  From  the  solution  gold  is  precipitated  elec- 
trolytically  or  by  adding  metallic  zinc. 

Refining  gold.  Gold  obtained  by  either  of  the  above  processes  is  not  pure, 
but  has  to  be  purified  or  refined  by  methods  which  differ  according  to  the  nature 
or  quantity  of  the  impurities  present,  or  according  to  the  use  to  be  made  of  the 
gold.  The  methods  employed  may  be  divided  into  two  classes,  viz.,  dry  and 
wet  processes.  In  the  dry  or  crucible  methods  the  operation  is  conducted  at  a 
temperature  sufficiently  high  to  melt  the  gold,  while  in  the  wet  processes  the 
dissolving  action  of  acids  is  made  use  of. 

Of  dry  methods  may  be  mentioned  the  following :  The  gold  is  fused  in  a 
clay  or  graphite  crucible  which  has  been  glazed  on  the  inside  with  borax,  and 
a  stream  of  chlorine  is  passed  through  the  molten  mass.  The  chlorides  of  zinc, 
bismuth,  arsenic,  and  antimony,  when  present,  are  volatilized,  while  the  chlo- 
rides of  silver  and  copper  rise  to  the  top,  forming,  with  some  of  the  borax,  a 
layer  over  the  purified  gold.  Another  method  consists  in  melting  the  gold  in 
a  crucible,  prepared  as  before  mentioned,  and  adding  gradually  a  mixture  of 
potassium  nitrate  and  carbonate  with  borax.  All  base  metals  are  converted 
into  oxides  which  become  dissolved  in  the  borax;  but  silver  is  not  eliminated 
by  this  method.  It  may,  however,  be  gotten  rid  of  by  heating  to  a  temperature 
just  below  fusion,  the  granulated  gold  with  about  one-sixth  of  its  weight  of 
sulphur.  The  mixture  should  be  protected  with  a  layer  of  fine  charcoal. 
Silver  sulphide  is  formed  during  the  operation  and  the  gold,  after  being  fused, 
may  be  cast  into  an  ingot  mold. 

Another  dry  method,  used,  however,  more  for  assaying  gold  ores  or  gold  alloys 
than  for  purifying  gold  on  a  large  scale,  is  the  cupellation  process.  It  depends 
on  the  solubility  of  gold  in  molten  lead  and  the  readiness  with  which  lead  takes 
up  oxygen  when  heated  in  an  oxidizing  flame.  In  carrying  out  the  process  the 
material  to  be  operated  on  is  fused  with  a  quantity  of  lead  amply  sufficient  to 
dissolve  the  metals  present.  The  resulting  alloy,  called  the  lead  button,  is  then 
submitted  to  fusion  on  a  very  porous  support,  made  of  bone-ash,  and  called  a 
cupel.  All  metals  except  gold  and  silver  are  oxidized ;  the  lead  oxide,  which  is 
fusible,  takes  up  all  other  oxides,  and  the  whole  of  this  mass  is  absorbed  by  the 
porous  bone-ash,  on  the  surf  ace  of  which  is  finally  left  a  button  of  gold  and  silver. 

Of  wet  processes  for  the  separation  of  gold  and  silver  is  to  be  mentioned  the 
method  known  as  parting.  It  depends  on  the  extraction  of  the  silver  (and  cop- 


GOLD.  365 

per,  if  present)  by  treating  the  granulated  alloy  with  nitric  acid  of  a  specific 
gravity  of  1.32.  This  dissolves  silver  and  copper,  but  does  not  act  on  the  gold. 
The  process,  however,  is  not  applicable  to  an  alloy  containing  more  than  33 
per  cent,  of  gold,  and  it  was  believed  that  it  should  not  exceed  25  per  cent. 
In  order  to  subject  to  this  process  an  alloy  which  is  richer  in  gold,  the  alloy  is 
first  fused  with  silver,  and  as  it  was  customary  to  use  3  parts  of  silver  for  1  part 
of  impure  gold  the  process  became  known  as  quartation  or  inquartation.  In 
place  of  nitric  acid,  sulphuric  acid  of  a  specific  gravity  of  1.84  may  be  used.  Gold 
which  has  been  freed  from  base  metals  and  silver  by  any  of  the  above-described 
methods  is  known  as  refined  gold,  but  it  is  rarely  absolutely  pure.  It  retains 
traces  of  base  metals  or  silver  and  all  of  the  platinum  if  originally  present. 

Chemically  pure  gold,  or  as  it  is  termed  by  the  mints  gold  1000  fine,  may  be 
obtained  by  the  following  process.  Nitro-hydrochloric  acid,  consisting  of  one 
part  of  nitric  acid  and  two  parts  of  hydrochloric  acid,  is  added  in  small  por- 
tions to  the  granulated  gold,  refined  by  one  of  the  ordinary  processes,  until  its 
solution,  with  the  aid  of  heat,  has  been  effected.  This  solution  of  gold  chloride 
is  evaporated  nearly  to  dryness  at  a  moderate  heat.  If  platinum  be  suspected 
the  remaining  mass  is  dissolved  in  very  little  water,  and  to  the  solution  is  added 
an  equal  volume  of  alcohol  and  some  ammonium  chloride.  If  platinum  be 
present  it  is  precipitated  as  ammonium  platinic  chloride  and  separated  by  fil- 
tration. The  filtrate  is  diluted  with  four  parts  of  water  and  permitted  to  stand 
for  several  days  in  order  to  cause  complete  precipitation  of  any  silver  chloride 
present.  To  the  filtrate  a  clear  solution  of  ferrous  sulphate  is  added  which 
causes  the  precipitation  of  gold.  After  decanting  the  supernatant  liquid  and 
thoroughly  washing  the  precipitate  with  distilled  water  it  is  treated  with  hot 
concentrated  acid,  to  eliminate  traces  of  iron  or  copper.  The  purified  gold  is 
again  washed,  dried,  fused  in  a  borax-lined  crucible  and  poured  into  an  ingot 
mold.  The  chemical  reaction  which  occurs  in  the  precipitation  of  gold  with 
ferrous  sulphate  is  this  : 

AuCl3  +  3FeS04  =  FeCl3  +  Fe2(SO4)3  +  Au. 

Many  other  reducing  agents  may  be  used  in  place  of  ferrous  sulphate  for 
the  precipitation  of  gold.     Thus  it  is  precipitated  in  a  spongy  or  crystalline 
condition  by  gently  heating  the  gold  solution  with  oxalic  acid: 
2AuCl3  +  3H2C2O4  =  6HC1  +  6CO2  +  2Au. 

Sulphurous  acid  precipitates  gold  in  scales: 

2AuCl3  -f-  3H,SO3  +  3H20  =  6HC1  +  3H2SO4  +  2Au. 
Zinc  and  many  other  base  metals  precipitate  gold  as  a  brown  powder: 
2AuCl3  -f  3Zn  =  3ZnCl2  +  2Au. 

Elementary  phosphorus,  and  many  other  organic  and  inorganic  reducing 
agents,  may  be  used  similarly  for  the  precipitation  of  gold  from  its  solutions, 
or  this  precipitation  may  be  effected  electrolytically. 

Cohesive  gold,  used  in  dentistry,  may  be  obtained  by  heating  gold  foil  to 
redness,  by  which  is  restored  its  cohesiveness,  which  is  greatly  diminished 
during  the  conversion  of  pieces  of  gold  into  foil  by  beating. 

Gold  is  orange-yellow  by  reflected  light,  and  green  by  transmitted 
light ;  it  fuses  at  1200°  C.  (2192°  F.),  has  a  specific  gravity  of  19.36, 


366  METALS  AND   THEIR   COMBINATIONS. 

and  is  a  good  conductor  of  heat  and  electricity.  It  is  so  malleable  and 
ductile  that  1  grain  can  be  hammered  into  a  film  covering  54  square 
inches,  and  can  be  drawn  into  a  wire,  if  protected  by  some  more  tena- 
cious metal  such  as  silver,  so  fine  that  1  grain  will  measure  550  feet. 
Tin,  lead,  antimony,  arsenic,  and  bismuth  destroy  the  ductility  and  malle- 
ability of  gold,  making  it  very  brittle.  A  small  proportion  of  platinum  con- 
fers upon  gold  elasticity  and  increases  its  hardness. 

Pure  gold  is  too  soft  for  general  use,  and  therefore  is  alloyed  with 
various  proportions  of  silver  and  copper.  It  is  customary  to  express 
the  purity  or  fineness  of  gold  in  carats,  an  old  term  meaning  a 
twenty-fourth  part.  Pure  gold  is  24  carats,  while  an  alloy  contain- 
ing 75  per  cent,  of  gold  is  said  to  be  of  18  carats  fineness.  Ameri- 
can coin  is  an  alloy  of  90  parts  of  gold  and  10  parts  of  copper ; 
jeweller's  gold  contains  generally  75  per  cent,  or  more  of  gold,  the 
other  metals  being  copper  and  silver ;  the  varying  proportions  are 
well  indicated  by  the  color. 

Gold  is  not  affected  by  either  hydrochloric,  nitric,  or  sulphuric 
acid,  but  is  dissolved  by  nitro-hydrochloric  acid,  by  free  chlorine  and 
bromine,  and  by  mercury,  with  which  it  forms  an  amalgam. 

Gold  is  trivalent  generally,  as  in  auric  chloride,  AuCl3,  but  also 
univalent  in  some  compounds,  as  in  aurous  chloride,  AuCl. 

Gold  chloride,  Au013  (Auric  chloride).  Obtained  by  dissolving 
pure  gold  in  nitro-hydrochloric  acid  and  evaporating  the  solution  to 
dryness.  A  mixture  of  equal  parts  by  weight  of  gold  chloride  and 
sodium  chloride  is  official  under  the  name  of  gold  and  sodium  chloride. 
It  is  an  orange-yellow,  very  soluble  powder,  containing  about  30  per 
cent,  of  metallic  gold. 

Tests  for  gold. 
(Solution  of  auric  chloride,  AuCl3,  may  be  used.) 

1.  Add  hydrogen  sulphide  to  the  solution  :  brown  auric  sulphide, 
Au2S3,  is  precipitated,  which  is  soluble  in  yellow  ammonium  sulphide. 

2.  Add  ferrous  sulphate  to  the  solution  and  set  aside  for  a  few 
hours— metallic  gold  is  precipitated  as  a  dark  powder  : 

AuCl3    +     3FeS04    =     Fe,(S04)s    -f     FeCl3    +     AU. 

3.  Many  other  reagents  cause  the  separation  of  metallic  gold  from 
its  solution,  as,  for  instance,  oxalic  acid,  sulphurous   and  arsenous 
acids,  potassium  nitrite,  etc. 


PLATINUM.  367 

Platinum,  Pt  =193.3.  Platinum,  like  gold,  is  found  in  nature  in 
the  free  state,  the  chief  supply  being  derived  from  the  Ural  mountains, 
where  it  is  associated  with  a  number  of  metals  (iridium,  ruthenium, 
osmium,  palladium,  rhodium)  resembling  platinum  in  their  properties. 

While  the  solubility  of  platinum  in  molten  lead  is  sometimes  used  for  its 
separation  by  the  cupellation  process  (see  refining  of  gold)  the  abstraction  of 
platinum  is  usually  accomplished  by  the  wet  process.  The  material  contain- 
ing it  is  treated  with  nitre-hydrochloric  acid  under  slight  pressure,  when  pla- 
tinic  chloride  is  formed.  The  solution  is  evaporated  to  dryness  and  the  mass 
heated  to  a  temperature  of  125°  C.  in  order  to  decompose  the  higher  chlorides 
of  iridium  and  palladium,  which  metals,  if  present,  would  otherwise  accompany 
the  platinum.  After  dissolving  the  residue  in  water,  ammonium  chloride  is 
added,  which  precipitates  platinum  as  ammonium  platinic  chloride,  PtCl4. 
2NH4C1.  The  washed  precipitate  when  heated  to  redness  is  completely  decom- 
posed, metallic  platinum  being  left  as  a  gray,  spongy  mass,  which  may  be  fused 
by  means  of  the  oxy-hydrogen  flame  or  in  an  electric  furnace. 

Platinum  is  of  great  importance  and  value  on  account  of  its  high 
fusing-point  and  its  resistance  to  the  action  of  most  chemical  agents, 
for  which  reason  it  is  used  in  the  manufacture  of  vessels  serving  in 
chemical  operations.  While  sulphuric,  nitric,  hydrochloric,  and  hydro- 
fluoric acids  have  no  action  on  platinum  it  is  readily  attacked  by 
chlorine,  and  at  a  red  heat  by  caustic  alkalies,  sulphur,  and  phosphorus. 

Platinum  is  of  a  silver-white  color  with  a  tinge  of  blue ;  it  is  very  malleable 
and  ductile ;  its  rate  of  expansion  by  heat  is  low,  about  that  of  glass.  This 
property  is  of  value  in  the  use  of  the  metal  for  the  pins  of  artificial  teeth,  and 
as  a  base  for  continuous  gum  work.  Addition  of  iridium  renders  platinum 
harder,  more  rigid  and  more  elastic,  all  of  which  properties  platinum  confers 
upon  silver  and  gold. 

The  property  of  platinum  to  condense  oxygen  upon  its  surface  and  to  dis- 
solve hydrogen  is  made  very  conspicuous  in  platinum  sponge  and  platinum  black. 
The  former  is  made  by  heating  precipitated  ammonium  chloroplatinate,  by 
which  a  gray  mass  of  finely  divided  platinum  is  left;  the  latter  is  obtained  as 
a  black  powder  by  adding  zinc  to  chloroplatinic  acid.  Either  of  these  forms 
or  platinum,  when  thrown  into  a  mixture  of  oxygen  and  hydrogen,  causes 
instant  explosion.  This  is  an  example  of  catalytic  action,  in  which  the  speed 
of  a  chemical  change  is  enormously  increased.  The  gases  condensed  in  the 
pores  of  the  finely  divided  metal  unite  rapidly  with  production  of  sufficient 
heat  to  cause  the  rest  of  the  gases  to  unite  with  explosion. 

Chloroplatinic  acid,  H2PtCl6.6H2O  (often  called  Platinic  chloride), 
is  obtained  as  reddish-brown  deliquescent  crystals  when  platinum  is 
dissolved  in  aqua  regia  and  the  solution  evaporated.  It  serves  as  a 
valuable  reagent  for  potassium  and  ammonium,  as  explained  in  con- 
nection with  the  analytical  reactions  of  these  bodies.  In  the  acid  and 


368  METALS  AND   THEIR  COMBINATIONS. 

its  salts  platinum  is  in  the  anion,  as  PtCl,/'.  The  chloride,  PtCl4,  is 
obtained  by  heating  the  chloroplatinic  acid  in  a  current  of  chlorine 
at  360°  C.  Its  solution  in  water  gives  red,  non-deliquescent  crystals 
of  the  composition,  H2PtCl4O.4H2O. 

Chloroplatinous  acid,  H2PtCl4,  results  when  platinous  chloride, 
PtCl2,  is  dissolved  in  hydrochloric  acid.  The  potassium  salt, 
K2PtCl4,  is  used  in  making  platinum  prints  in  photography.  The 
corresponding  barium  platinocyanide,  BaPt(CN)4.4H2O,  forms  light 
yellow  crystals.  Screens  coated  with  this  salt  become  luminous  when 
Rontgen  rays  (#-rays)  fall  upon  them.  Such  fluorescent  screens  are 
used  for  observing  x-ray  pictures.  Ultra-violet  and  radium  rays  also 
affect  the  screens. 

Iridium,  Ir  =  191.5.  This  element  has  been  mentioned  as  one  of  the  metals 
which  accompany  platinum  in  nature.  It  is  obtained  from  the  material  left 
in  the  working  of  platinum  ores. 

Iridium  has  a  grayish- white  color  and  resembles  polished  steel ;  it  is  harder, 
more  brittle,  specifically  heavier  and  less  fusible  than  platinum.  The  increased 
hardness,  rigidity  and  elasticity  which  iridium  imparts  to  platinum  makes  the 
alloy  a  valuable  dental  material.  Gold  pens  are  often  tipped  with  iridium 
which  renders  them  more  durable. 

Compact  pieces  of  iridium  are  insoluble  in  all  acids;  when  finely  divided  it 
dissolves  in  nitro-hydrochloric  acid.  It  is  for  these  reasons  that  most  of  the 
iridium  is  left  in  the  residue  of  the  material  from  which  platinum  has  been 
extracted.  Several  oxides,  hydroxides  and  chlorides  of  iridium  are  known. 

Molybdenum,  Mo  =  95.3.  This  metal  is  found  in  nature  chiefly  as  sul- 
phide, MoS.2,  from  which,  by  roasting,  molybdic  oxide.  MoO3,  is  obtained.  The 
oxide,  when  dissolved  in  water,  forms  an  acid  which  combines  with  metals, 
forming  a  series  of  salts  termed  molybdates.  Of  interest  is  ammonium  molyb- 
date,  a  solution  of  which  in  nitric  acid  is  an  excellent  reagent  for  phosphoric- 
acid,  with  which  it  forms  a  yellow  precipitate,  insoluble  in  acids,  soluble  in 
ammonium  hydroxide. 


QUESTIONS. — How  is  antimony  found  in  nature,  and  what  are  the  proper- 
ties of  this  metal  ?  State  the  composition  of  antimonous  sulphide,  and  its 
color  when  crystallized  and  amorphous.  How  do  hydrochloric  acid  and  alkali 
hydroxides  act  upon  antimonous  sulphide?  Mention  the  two  chlorides  of 
antimony  and  state  their  properties.  How  is  antimonous  oxide  made,  and  for 
what  is  it  used?  Give  tests  for  antimony.  State  the  use  made  of  tin  in  the 
metallic  state;  mention  the  two  chlorides  of  tin,  and  the  use  of  stannous  chlo- 
ride. Describe  processes  for  refining  gold  by  the  dry  and  wet  methods.  How 
are  gold  and  platinum  found  in  nature ;  by  what  acid  may  they  be  dissolved, 
and  what  is  the  composition  of  the  compounds  formed?  Which  is  the  most 
important  compound  of  molybdenum,  and  what  is  its  use? 


THE  ARSENIC  GROUP. 


369 


Summary  of  analytical  characters  of  metals  of  the  arsenic 

group. 


Arsenic. 

Antimony. 

Tin. 

Gold. 

Platinum. 

Hydrogen  sulphide    . 

Precipitate  heated  ^j 
in  strong  hydro-  y 
chloric  acid  .     .  J 

Potassium  hydroxide 

Yellow  pre- 
cipitate. 

Insoluble. 

Orange 
precipitate 

Soluble. 
White 

Yellow 
or  brown 
precipitate. 

Soluble. 
White 

Black 
precipitate 

Insoluble. 
Brownish 

Dark- 
brown 
precipitate. 

Insoluble. 
1  With  ex- 

Ammonia water 

precipitate, 
soluble 
in  excess. 

White 

precipitate, 
soluble 
in  excess. 

White 

precipitate, 
soluble 
in  excess. 

Brownish 

cess  of 
hydro- 
chloric 
f     acid  a 
yellow 

Gutzeit's  test 

Yellow  stain 

precipitate. 
Dark  stain 

precipitate. 

yellow 
precipitate 

precipi- 
J      tate. 

Fleitmann's  test 

turning  dark 
with  water. 

Dark  stain 

24 


V. 

ANALYTICAL  CHEMISTRY. 


34.    INTRODUCTORY  REMARKS  AND  PRELIMINARY 
EXAMINATION. 

General  remarks.  Analytical  chemistry  is  that  part  of  chemistry 
which  treats  of  the  different  analytical  methods  by  which  substances 
are  recognized  and  their  chemical  composition  determined.  This 
determination  may  be  either  qualitative  or  quantitative,  and,  accord- 
ingly, a  distinction  is  made  between  a  qualitative  analysis,  by  which 
simply  the  nature  of  the  elements  (or  groups  of  elements)  present  in 
the  substance  under  examination  is  determined,  and  a  quantitative 
analysis,  by  which  also  the  exact  amount  of  these  elements  is  ascer- 
tained. 

In  this  book  qualitative  analysis  will  be  considered  chiefly,  as  the 
methods  for  quantitative  determinations  of  the  different  elements  are 
so  numerous  and  so  varied  that  a  detailed  description  of  them  would 
occupy  more  space  than  can  be  devoted  to  analytical  chemistry  in  this 
work.  Some  brief  directions  concerning  quantitative  determinations, 
especially  by  volumetric  methods,  are  given  in  Chapter  38.  Every- 
one studying  analytical  chemistry  should  do  it  practically,  that  is, 
should  perform  for  himself  in  a  laboratory  all  those  reactions  which 
have  been  mentioned  heretofore  as  characteristic  of  the  different  ele- 
ments and  their  compounds,  and,  furthermore,  should  make  himself 
acquainted  with  the  methods  by  which  substances  are  recognized 
when  mixed  with  others,  by  analyzing  various  complex  substances. 

Such  a  course  of  practical  work  in  a  suitable  laboratory  is  of  the 
greatest  advantage  to  all  studying  chemistry,  and  students  cannot  be 
too  strongly  advised  to  avail  themselves  of  any  facilities  offered  in 
performing  chemical  experiments,  analytically  or  otherwise. 

Apparatus  needed  for  qualitative  analysis. 

1.  Iron  stand.     (Fig.  48.) 

2.  Bunsen  lamp  with  flexible  tube  (Fig.  48)  or  (where  without  gas-supply) 

spirit-lamp  and  alcohol. 

371 


372 


ANALYTICAL  CHEMISTRY. 


3.  Test-tube  stand  and  one  dozen  assorted  test-tubes.     (Fig.  49.) 

4.  Three  beakers  from  100  to  150  c.c.  capacity.     (Fig.  50,  A.) 

5.  Two  flasks  of  100  to  150  c.c.  capacity.     (Fig.  50,  B.) 

FIG.  48. 


FIG.  49. 


FIG.  50. 


6.  Wash-bottle  of  about  400  c.c.  capacity.     (Fig.  51,  A.) 

7.  Three  small  glass  funnels,  about  one  and  a  half  to  two  inches  in  diameter. 

(Fig.  51,  B.) 


INTRODUCTORY  REMARKS. 


373 


8.  A  few  pieces  of  glass  tubing  about  ten  inches  long,  and  some  India-rubber 

tubing  to  fit  the  glass  tubing. 

9.  Three  glass  rods. 

FIG.  51. 


10.  Three  small  porcelain  evaporating  dishes,  about  two  inches  in  diameter. 

(Fig.  52,  A.) 

11.  Blowpipe.     (Fig.  52,  B.) 

12.  Crucible  tongs.     (Fig.  52,  C.) 

FIG.  52. 


13.  Round  and  triangular  file 

14.  Wire  gauze,  about  six  inches  square,  or  sand  tray. 

15.  One  square  inch  of  platinum  foil  (not  too  light),  and  six  inches  of 

platinum  wire. 

16.  Filter-paper. 

17.  Pair  of  scissors. 

18.  One  or  two  dozen  assorted  corks. 

19.  Sponge  and  towel. 

20.  Two  watch-glasses. 

21.  Small  pestle  and  mortar.     (Fig.  52,  D.) 

22.  Small  porcelain  crucible. 

23.  Small  platinum  crucible.     (Fig.  52,  E.) 

24.  Wire  triangle  to  support  the  crucible.     (Fig.  52,  F.) 


374  ANALYTICAL   CHEMISTRY. 

Reagents  needed  in  qualitative  analysis. 
a.  Liquids. 

1.  Sulphuric  acid,  sp.  gr.  1.84,  H2SO4. 

2.  Sulphuric  acid  diluted,  sp  gr   1.068  (1  part  sulphuric  acid,  9  parts  water). 

3.  Hydrochloric  acid,  sp.  gr.  1.16,  HC1. 

4-  Hydrochloric  acid  diluted,  sp.  gr.  1.049   (6  parts  hydrochloric  acid,  13  parts 
water). 

5.  Nitric  acid,  sp.  gr.  1.42,  HNO3. 

6.  Acetic  acid,  sp.  gr.  1.048,  C2H4O2. 

7.  Hydrogen  sulphide,  either  the  gas  or  its  solution  in  water,  H2S. 

8.  Ammonium  sulphide,  (NH4)2S. 

9.  Ammonium  hydroxide  (ammonia  water),  NH4OH. 

10.  Ammonium  carbonate,  (NH4)2CO3.     A  solution  of  one  part  of  the  commercial 

salt  in  a  mixture  of  four  parts  of  water  and  one  part  of  ammonia  water. 

11.  Ammonium  chloride,  NH4C1 ;  ten  per  cent  solution. 

12    Ammonium  oxalate,  (NH4)2C2O4;  five  per  cent,  solution. 

13.  Ammonium  molybdate,  (NH4)2MoO4-     A  five  per  cent  solution  of  the  salt  in  a 

mixture  of  equal  parts  of  water  and  nitric  acid. 

14.  Sodium  hydroxide,  NaOH.  ~| 

15.  Sodium  carbonate, 


16.  Sodium  phosphate,  Na«HPOA.  m  i  .- 

,_    c,   ,.  }-    Ten  per  cent,  solutions. 

17.  Sodium  acetate,  NaC2H3O2. 

18  Potassium  chromate,  K2CrO4. 

19  Potassium  dichromate,  K2Cr2Or 
20.  Potassium  iodide,  KI 

21    Potassium  ferrocyanide,  K4Fe(CN)8.  ,-,. 

oo    T>  *  f     •         -j     T^  ™    /nxTx  r    Five  per  cent,  solutions. 

22.  Potassium  ferricyanide,  K6Fe2(CN)12. 

23    Potassium  sulphocyanate,  KCNS. 

24.  Magnesium  sulphate,  MgSO4.  ^ 

25.  Barium  chloride,  BaCl2.  L    Ten  per  cent,  solutions. 

26.  Calcium  chloride.  CaCl2.  ) 

27.  Calcium  hydroxide,  CaiOH)2  (lime-water).  1 

28  Calcium  sulphate,  CaSO,  I    Crated  solutions. 

29  Ferric  chloride,  FeCl3.  n 

30  Lead  acetate,  Pb.(C2H302)2. 

31.  Silver  nitrate,  AgNO3.  [    Five  per  cent,  solutions. 

32.  Mercuric  chloride,  HgCl2. 

33.  Platinic  chloride,  H2PtCle. 

34.  Stannous  chldride,  SnCl2.2H2O;  ten  per  cent,  solution. 

35.  Solution  of  indigo 

36.  Alcohol,  C2H5OH. 

37.  Sodium  cobaltic  nitrite  solution,  Co2(NO2)6.6NaNO2  +  H2O.     Four  grammes  of 

cobaltous  nitrate,  Co(NO3)2.6H2O,  and  10  grammes  of  sodium  nitrite,  NaNO.., 
are  dissolved  in  about  50  c.c.  of  water,  2  c.c.  of  acetic  acid  are  added,  and  then 
water  to  make  100  c.c. 

38.  Alkaline  mercuric-potassium  iodide  solution  (Nessler's  solution).     Five  grammes 

of  potassium  iodide  are  dissolved  in  hot  water,  and  to  this  is  added  a  hot 
olution,  made  by  dissolving  2.5  grammes  of  mercuric  chloride  in  10  c.c.  of 
water.  To  the  turbid  red  mixture  is  added  a  solution  made  by  dissolving  16 


INTRODUCTORY  REMARKS.  375 

grammes  of  potassium  hydroxide  in  40  c.c.  of  water,  and  the  whole  diluted  to 
100  c.c.  Some  mercuric  iodide  deposits  on  cooling,  and  may  be  left  in  the 
bottle,  the  clear  solution  being  decanted  as  needed. 

b.  Solids. 

1.  Litmus  or  blue  and  red  litmus  paper. 
2    Turmeric  paper. 

3.  Sodium  carbonate,  dried,  Na2CO3. 

4.  Sodium  biborate,  borax,  Na2B4O7.10H2O. 

5.  Sodium-ammonium-hydrogen  phosphate  (microcoamic  salt), 

Na(NH4)HPO4.4H2O. 

6.  Potassium  carbonate,  K2CO3. 

7.  Potassium  nitrate,  KNO3. 

8.  Potassium  chlorate,  KC1O3. 

9.  Potassium  permanganate,  KMnO4. 
10-  Potassium  cyanide,  KCN. 

11.  Calcium  hydroxide,  Ca(OH)2. 

12.  Ferrous  sulphide,  FeS. 

13.  Ferrous  sulphate,  FeSO4.7H2O. 

14.  Manganese  dioxide,  MnO2. 

15.  Zinc,  granulated,  Zn. 

16.  Copper,  Cu. 

17.  Cupric  oxide,  CuO. 

18.  Cupric  sulphate,  CuSO4  5H,O. 

19.  Tartaric  acid,  H2C4H4O6. 

20.  Tannic  acid,  H  CUH9O9 

21.  Pyrogallic  acid,  C6H3(OH)3. 

22.  Diphenylamine,  (C6H5)2NH. 

23.  Starch,  C6H10O5. 

While  the  apparatus  and  reagents  here  enumerated  are  the  more 
important  ones,  the  analyst  will  occasionally  require  others  not  men- 
tioned in  the  above  list. 

General  mode  of  proceeding-  in  qualitative  analysis.  Every 
step  taken  in  analysis  should  be  properly  written  down  in  a  note- 
book, and  these  remarks  should  be  made  directly  after  a  reaction  has 
been  performed,  and  not  after  the  nature  of  the  substance  has  been 
revealed  by  perhaps  numerous  reactions. 

Not  only  the  reactions  by  which  positive  results  have  been  obtained 
should  be  noted,  but  also  those  tests  and  reagents  mentioned  which 
have  been  applied  with  negative  results — that  is,  which  have  been 
applied  without  revealing  the  presence  of  any  substance,  or  any  group 
of  substances.  Such  negative  results  are,  however,  positive  in  so  far 
as  they  prove  the  absence  of  a  certain  substance,  or  certain  substances, 
for  which  reason  they  are  of  direct  value,  and  should  be  noted. 

In  comparing,  finally,  the  result  obtained  by  the  analysis  with  the 


376  ANALYTICAL   CHEMISTRY. 

notes  taken  during  the  examination,  none  of  them  should  be  contra- 
dictory to  the  conclusions  drawn.  If,  for  instance,  the  preliminary 
examination  showed  the  substance  to  have  been  volatilized  by  heating 
upon  platinum  foil  with  the  exception  of  a  very  slight  residue,  and  if, 
afterward,  other  tests  show  the  presence  of  ammonia  and  hydro- 
chloric acid  and  the  absence  of  everything  else,  and  if,  then,  the  con- 
clusion be  drawn  that  the  substance  is  pure  ammonium  chloride,  this 
conclusion  must  be  incorrect,  because  pure  ammonium  chloride  is 
wholly  volatile,  and  does  not  leave  a  residue.  It  will  then  be  the  task 
of  the  operator  to  find  where  the  mistake  occurred,  and  to  correct  it. 

Use  of  reagents.  A  mistake  made  by  most  beginners  in  analyz- 
ing is  the  use  of  too  large  quantities  both  of  the  substance  applied 
for  testing  and  of  the  reagents  added.  This  excessive  use  of  material 
is  not  only  a  waste  of  money,  but,  what  is  of  greater  importance,  a 
waste  of  time.  Some  experience  in  analyzing  will  soon  convince  the 
student  of  the  truth  contained  in  this  remark,  and  will  also  enable 
him  to  select  the  correct  quantities  of  materials  to  be  used,  which 
rarely  exceed  0.2-1.0  gramme.  A  smaller  amount — in  fact,  as  little 
as  a  few  milligrams — frequently  may  answer,  and  a  much  larger 
quantity  may  occasionally  be  needed,  as,  for  instance,  in  cases  where 
highly  diluted  reagents,  such  as  calcium  sulphate  solution,  lime- 
water,  hydrogen  sulphide  water,  etc.,  are  applied. 

Preliminary  examination.  This  examination  includes  the  fol- 
lowing points : 

1.  Physical  properties.     Solid  or  liquid;  crystallized  or  amor- 
phous; color,  odor,  hardness,  gravity,  etc.     (On  account  of  possible 
poisonous  properties,  the  greatest  care  should  be  exercised  in  tasting 
a  substance.) 

2.  Action  on  litmus.     Examined  by  holding  litmus-paper  in  the 
liquid,  or  by  placing  the  powdered  solid  upon  red  and  blue  litmus- 
paper,  moistened  with  water.     (It  should  be  remembered  that  many 
normal  salts,  as,  for  instance,  aluminum  sulphate,  ferrous  sulphate, 
etc.,  have  an  acid  reaction  to  litmus-paper,  and  that  such  a  reaction 
consequently  is  not  conclusive  of  the  presence  of  a  free  acid,  nor  even 
of  an  acid  salt.) 

3.  Heating  on  platinum  foil  or  in  a  dry  glass  tube,  open  at 
both  ends.     (If  the  substance  to  be  examined  be  a  liquid,  it  should 


INTRODUCTORY  REMARKS.  377 

be  evaporated  in  a  small  porcelain  dish  to  see  whether  a  solid  residue 
be  left  or  not.  If  a  residue  be  left,  it  should  be  treated  like  a  solid.) 
The  heating  of  a  small  quantity  of  a  solid  substance  upon  platinum 
foil,  or  upon  a  piece  of  mica,  held  over  the  flame  of  a  Bunsen  burner, 
is  a  test  which  should  never  be  omitted,  as  it  discloses  in  most  cases 
the  fact  whether  the  substance  is  of  an  organic  or  inorganic  nature. 

Most  organic  (non-volatile)  substances  when  thus  heated  will  burn  with  a 
luminous  flame,  leaving  in  many  cases  a  black  residue  of  carbon,  which  upon 
further  heating  disappears.  In  cases  where  the  organic  nature  of  a  compound 
is  not  clearly  demonstrated  by  heating  on  platinum  foil,  the  substance  is  heated 
with  an  excess  of  cupric  oxide  in  a  test-tube  or  other  glass  tube,  provided  with 
a  delivery-tube  which  passes  into  lime-water.  Upon  heating  the  mixture  the 
carbon  of  the  organic  matter  is  converted  into  carbon  dioxide,  which  renders 
lime-water  turbid. 

The  analytical  processes  by  which  the  nature  of  an  organic  substance  is 
determined  are  not  considered  in  this  part  of  the  book,  but  will  be  mentioned 
when  considering  the  carbon  compounds.  Some  substances  ruin  platinum  when 
heated  on  it.  Thus,  salts  of  easily  reducible  metals,  as  lead,  bismuth,  antimony, 
tin,  especially  their  organic  salts,  are  apt  to  do  so,  because  these  metals  form 
fusible  alloys  with  the  platinum.  Thiosulphates  corrode  and  hypophosphites 
destroy  platinum.  Should  the  presence  of  any  of  the  substances  be  suspected, 
heating  on  platinum  should  be  omitted.  Indeed,  tests  4  and  5  can  be  applied 
first,  as  they  may  show  the  presence  of  these  objectionable  substances. 

An  inorganic  substance  heated  on  platinum  foil  may  either  be  volatilized, 
change  color,  become  oxidized,  suffer  decomposition,  or  remain  unchanged. 
(See  Table  I.,  page  381.) 

FIG.  53.  FIG.  54. 


Heating  of  solids  in  bent  glass  tube.  Heating  on  charcoal  by  means  of  blowpipe. 

Some  substances,  containing  small  quantities  of  water  enclosed 
between  the  crystals  (common  salt,  for  instance),  decrepitate  when 
heated,  the  small  fragments  being  thrown  from  the  foil;  such  sub- 


378  ANALYTICAL   CHEMISTRY. 

stances  should  be  heated  in  a  dry  test-tube  to  expel  the  water  and 
then  be  examined  on  platinum  foil. 

In  many  cases  it  is  preferable  to  heat  the  substance  in  a  bent  glass 
tube,  as  shown  in  Fig.  53,  instead  of  on  platinum  foil,  because  vola- 
tile products  evolved  during  the  process  of  heating  may  become  re- 
condensed  in  the  cooler  part  of  the  tube,  and  thus  saved  for  further 
examination. 

The  presence  of  water,  sulphur,  mercury,  arsenic,  etc.,  may  often 
be  readily  demonstrated  by  this  mode  of  operating. 

4.  Heating1  on  charcoal  by  means  of  the  blowpipe.     This  test 
reveals  the  presence  of  chlorates  and  nitrates  by  the  vivid  combus- 
tion of  the  charcoal  (known  as  deflagration),  which  takes  place  in 
consequence  of  the  oxidizing  action  of  these  substances. 

Arsenic  is  indicated  by  a  characteristic  odor  of  garlic. 

5.  Heating-  on  charcoal  with  sodium  carbonate  and  potas- 
sium cyanide.     A  small  quantity  of  the  finely  powdered  substance 
is  mixed  with  twice  its  weight  of  potassium  cyanide  and  dry  sodium 
carbonate.     This  mixture  is  placed  in  a  small  hole  made  in  a  piece 
of  charcoal,  and  heat  applied  by  means  of  the  blowpipe  (see  Fig.  54). 
Many  metallic  compounds  may  be  recognized  by  this  test,  the  metals 
being  liberated  and  found  as  metallic  globules  or  shining  particles  in 
the  fused  mass  after  this  has  been  removed  from  the  charcoal  and 
washed  with  water  in  a  small  mortar.     (See  Fig.  55.) 

FIG.  55. 


A  characteristic  incrustation  is  formed  by  some  metals,  due  to  the 
precipitation  of  a  metallic  oxide  around  the  heated  spot  on  the  char- 
coal. 

If  sulphur  as  such,  or  in  any  form  of  combination,  be  present  in 
the  substance  examined  by  this  test,  the  fused  mass  contains  a  sulphide 
of  the  alkali  (hepar),  which  may  be  recognized  by  placing  it  en  a 
piece  of  bright  silver  (coin)  moistened  with  a  drop  of  water,  when  the 


INTRODUCTORY  REMARKS.  879 

silver  will  be  stained  black  in  consequence  of  the  formation  of  silver 
sulphide.  The  presence  of  the  alkali  sulphide  may  also  be  demon- 
strated by  the  addition  of  a  few  drops  of  hydrochloric  acid  to  the 
fused  mass,  when  hydrogen  sulphide  is  evolved  and  may  be  recog- 
nized by  its  odor. 

6.  Flame  tests.  Many  substances  impart  a  characteristic  color 
to  a  non-luminous  flame.  The  best  mode  of  performing  this  test  is 
as  follows :  A  platinum  wire  is  cleaned  by  washing  in  hydrochloric 
acid  and  water,  and  heating  it  in  the  flame  until  the  latter  is  no 
longer  colored.  One  end  of  the  wire  is  fused  in  a  short  piece  of 
glass  tubing  (see  Fig.  56),  the  other  end  is  bent  so  as  to  form  a  small 

FIG.  56. 


loop,  which  is  heated,  dipped  into  the  substance  to  be  examined,  and 
again  held  in  the  lower  part  of  the  flame,  which  then  becomes  colored. 

Some  substances  show  the  color-test  after  being  moistened  with 
hydrochloric  or  sulphuric  acid. 

A  second  method  of  showing  flame  reactions  is  to  mix  the  substance 
with  alcohol  in  a  small  dish ;  the  alcohol,  upon  being  ignited,  shows 
a  colored  flame,  especially  in  the  dark. 

7.  Colored  borax  beads.  The  compounds  of  some  metals  when 
fused  with  glass,  impart  to  it  characteristic  colors.  For  analytical 
purposes  not  the  silica-glass,  but  borax-glass  is  generally  used.  This 
latter  is  made  by  dipping  the  loop,  of  a  platinum  wire  in  powdered 
borax  and  heating  it  in  the  flame  (directly,  or  by  means  of  the  blow- 
pipe) until  all  water  has  been  expelled  and  a  colorless,  transparent 
bead  has  been  formed.  To  this  colorless  bead  a  little  of  the  finely 
powdered  substance  is  added  and  the  bead  strongly  heated.  The 
metallic  compound  is  chemically  acted  upon  by  the  boric  acid,  a  bo  rate 
being  formed  which  colors  the  bead  more  or  less  intensely,  according 
to  the  quantity  of  the  metallic  compound  used. 

Some  metals  (copper,  for  instance)  forming  two  series  of  compounds  give 
different  colors  to  the  bead  when  present  in  either  the  higher  or  the  lower  state 
of  oxidation. 

By  modifying  the  blowpipe  flame  so  as  either  to  oxidize  (by  supplying  an 
excess  of  atmospheric  oxygen),  or  deoxidize  (by  allowing  some  unburnt  carbon 
in  the  flame),  the  metallic  compound  in  the  bead  may  be  made  to  assume  the 


380  ANALYTICAL   CHEMISTRY. 

higher  or  lower  state  of  oxidation.  A  copper  bead  may  thus  be  changed  from 
blue  to  red,  or  red  to  blue,  the  blue  bead  containing  the  copper  in  the  cupric, 
the  red  bead  in  the  cuprous  form.  In  some  cases  microcosmic  salt,  NaNH4HPO4, 
is  used  for  making  the  bead. 

8.  Liquefaction  of  solid  substances.  Most  solid  substances 
have  to  be  dissolved  for  analysis.  The  solution  obtained  may  be 
either  a  simple  or  chemical  solution.  In  a  simple  solution  the  dis- 
solved body  retains  all  of  its  original  properties,  with  the  exception 
of  its  shape,  and  may  be  re-obtained  by  evaporation.  Sodium 
chloride  and  sugar  dissolved  in  water  form  simple  solutions.  A 
chemical  solution  is  one  in  which  the  chemical  composition  of  the  sub- 
stance has  been  changed  during  the  process  of  dissolving,  as,  for 
instance  when  calcium  carbonate  is  dissolved  in  hydrochloric  acid ; 
this  solution  now  contains  and  leaves  on  evaporation  calcium 
chloride.  The  solvents  used  are  water,  or  the  mineral  acids  for 
substances  insoluble  in  water,  especially  dilute,  or,  if  necessary,  strong 
hydrochloric  acid.  The  dissolving  action  of  the  acid  should  be  facil- 
itated by  the  aid  of  heat.  Nitric  or  even  nitro-hydrochloric  acid 
may  have  to  be  used  in  some  cases. 

Three  mistakes  ore  frequently  made  by  beginners  in  dissolving  sub- 
stances in  acids ,  viz. :  The  substance  is  not  powdered  as  finely  as  it 
should  be  ;  sufficient  time  is  not  given  for  the  acid  to  act ;  too  large  an 
excess  of  the  acid  is  used. 

If  a  substance  is  partly  dissolved  by  water  and  partly  by  one  or 
more  other  solvents,  it  may  be  well  to  examine  the  different  solutions 
separately. 

Substances  insoluble  in  water  and  in  acids  have  to  be  rendered 
soluble  by  fusion  with  a  mixture  of  potassium  and  sodium  carbonate, 
or  with  potassium  acid  sulphate,  or  by  the  action  of  hydrofluoric 
acid. 

The  insoluble  sulphates  of  the  alkaline  earths,  when  fused  with  the 
alkaline  carbonates,  are  con  verted  into  carbonates,  while  the  sulphates 
of  the  alkalies  are  formed.  The  latter  compounds  may  be  eliminated 
by  washing  the  fused  mass  with  water  and  filtering :  the  solid  residue 
upon  the  filter  contains  the  carbonates  of  the  alkaline  earths,  which 
may  be  dissolved  in  hydrochloric  acid. 

Insoluble  silicates  may  be  decomposed  by  the  methods  mentioned 
on  page  186. 


I y TROD  UCTOR  Y  REMA RKS. 


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382  ANALYTICAL  CHEMISTRY. 

35.   SEPARATION  OF  METALS  INTO  DIFFERENT  GROUPS. 

General  remarks.  The  preliminary  examination  will,  in  most 
cases,  decide  whether  or  not  a  metal  or  metals  are  present  in  the  sub- 
stance to  be  examined.  If  there  be  metals,  the  solution  should  be 
treated  according  to  Table  II.,  page  344,  in  order  to  find  the  group 
or  groups  to  which  these  metals  belong,  and  also  to  separate  them 
into  these  groups,  the  individual  nature  of  the  metals  themselves 
being  afterward  demonstrated  by  special  methods. 

The  simplest  method  of  separating  from  each  other  the  57  metals 
known,  if  all  were  in  one  solution,  would  be  to  add  successively  57 
different  reagents,  each  of  which  should  form  an  insoluble  compound 
with  but  one  of  the  metals.  By  separating  this  insoluble  compound 
from  the  metals  remaining  in  solution  (by  filtration),  and  by  thus  pre- 
cipitating one  metal  after  the  other,  they  all  could  be  easily  separated. 
We  have,  however,  no  such  57  reagents,  and  are,  consequently,  com- 
pelled to  precipitate  a  number  of  metals  together,  and  the  reagents 
used  for  this  purpose  are  known  as  group-reagents. 

They  are : 

1.  Hydrogen  sulphide,  added  to  the  solution  previously  acidified  by 
hydrochloric  acid.     Precipitated  are  :  the  metals  of  the  arsenic  and 
lead  groups  as  sulphides. 

2.  Ammonium  sulphide,  added  after  supersaturating  with  ammonium 
hydroxide.     Precipitated  are :  the  metals  of  the  iron  group  and  of 
the  earths  as  sulphides  or  hydroxides. 

3.  Ammonium  carbonate.     Precipitated  are :   the  metals  of    the 
alkaline  earths  as  carbonates. 

4.  In  solution  are  left :  the  metals  of  the  alkalies  and  magnesium. 
The  order  in  which   these  group-reagents  are  added  cannot  be 

QUESTIONS. — What  is  analytical  chemistry,  and  what  is  the  object  of  quali- 
tative and  of  quantitative  analysis?  What  properties  of  a  substance  should 
be  noticed  first  in- making  a  qualitative  analysis?  By  what  tests  may  organic 
compounds  be  distinguished  from  inorganic  compounds?  Explain  the  terms 
decrepitation  and  deflagration.  Mention  some  substances  which  are  completely 
volatilized  by  heat,  some  which  are  fusible,  and  some  which  are  not  changed 
by  heating  them.  What  is  meant  by  "  hepar,"  and  which  element  is  indicated 
by  the  formation  of  hepar?  Mention  some  metals  which  may  be  liberated 
from  their  compounds  by  heating  on  charcoal  with  potassium  cyanide  and  car- 
bonate. Which  metallic  compounds  and  which  acids  are  capable  of  coloring  a 
non-luminous  flame?  Name  the  colors  imparted.  State  the  metals  which  im- 
part characteristic  colors  to  a  borax  bead.  Which  solvents  are  used  for  lique- 
fying solids,  and  what  precautions  should  be  observed  in  this  operation? 


SEPARATION  OF  METALS  INTO  DIFFERENT  GROUPS.      383 

reversed  or  changed,  because  ammonium  sulphide  added  first  would 
precipitate  not  only  the  metals  of  the  iron  group  and  the  earths,  but 
also  the  metals  of  the  lead  group ;  .ammonium  carbonate  would  pre- 
cipitate also  most  of  the  heavy  metals. 

For  the  same  reasons,  in  separating  metals  of  the  different  groups,  the  group- 
reagents  must  be  added  in  excess,  that  is,  enough  of  them  must  be  added  to 
precipitate  the  total  quantity  of  the  metals  of  one  group,  before  it  is  possible 
to  test  for  metals  of  the  next  group.  Suppose,  for  instance,  a  solution  to  con- 
tain a  salt  of  bismuth  only.  Upon  the  addition  of  hydrogen  sulphide  to  the 
acidified  solution,  a  dark-brown  precipitate  (of  bismuth  sulphide)  is  produced, 
indicating  the  presence  of  a  metal  of  the  lead  group.  Suppose,  further,  that 
hydrogen  sulphide  has  not  been  added  in  sufficient  quantity  to  precipitate  the 
whole  of  the  bismuth,  then  ammonium  sulphide,  as  the  next  group-reagent, 
would  produce  a  further  precipitation  in  the  filtrate,  which  fact  would  lead  to 
the  assumption  that  a  metal  of  the  iron  group  was  present,  which,  however, 
would  not  be  the  case. 

If  the  solution  contain  but  one  metal,  the  group-reagents  are  added 
successively  in  small  quantities  to  the  same  solution,  until  tJ*e  reagent 
is  found  which  causes  a  precipitation,  which  reagent  is  then  added  in 
somewhat  larger  quantity  in  order  to  produce  a  sufficient  amount  of 
the  precipitate  for  further  examination. 

Acidifying-  the  solution.  Hydrogen  sulphide  has  to  be  added 
to  the  acidified  solution  for  two  reasons,  viz. :  In  a  neutral  or  alkaline 
solution  some  metals  of  the  arsenic  group  (which  are  to  be  pre- 
cipitated) would  not  be  precipitated  by  hydrogen  sulphide ;  some  of 
the  metals  of  the  iron  group  (which  are  not  to  be  precipitated)  would 
be  thrown  down. 

The  best  acid  to  be  used  in  acidifying  is  dilute  hydrochloric  acid ; 
but  this  acid  forms  insoluble  compounds  with  a  few  of  the  metals  of 
the  lead  group,  causing  them  to  be  precipitated.  Completely  pre- 
cipitated by  hydrochloric  acid  are  mercurous  and  silver  compounds ; 
partially  precipitated  are  compounds  of  lead,  chloride  of  lead  being 
somewhat  soluble  in  water.  The  precipitate  formed  by  hydrochloric 
acid  may  be  examined  by  Table  III.,  page  387. 

Hydrochloric  acid  added  to  a  solution  may,  in  a  few  cases  (other 
than  those  just  mentioned),  cause  a  precipitate,  as,  for  instance,  when 
added  to  solutions  containing  certain  compounds  of  antimony  or  bis- 
muth (the  precipitated  oxychlorides  of  these  metals  are  soluble  in 
excess  of  the  acid),  to  metallic  oxides  or  hydroxides  which  have  been 
dissolved  by  alkali  hydroxides  (for  instance,  hydroxide  of  zinc  dis- 
solved in  potassium  or  ammonium  hydroxide),  to  solutions  of  alkali 
silicates,  when  silica  separates,  etc. 


ANALYTICAL   CHEMISTRY. 

Addition  of  hydrogen  sulphide.  This  reagent  is  employed 
either  in  the  gaseous  state  (by  passing  it  through  the  heated  solution) 
or  as  hydrogen  sulphide  water.  The  latter  reagent  answers  in  those 
cases  where  but  one  metal  is  present;  if,  however,  metals  of  the 
arsenic  and  lead  groups  are  to  be  separated  from  metals  of  other 
groups,  the  gas  must  be  used. 

FIG.  57  F'«-58- 


Apparatus  for  generating  hydro- 
gen sulphide. 


Apparatus  for  generating  hydro- 
gen sulphide. 


For  generating  hydrogen  sulphide  the  directions  given  on  page  214  may,, 
be  followed.  In  place  of  the  apparatus  there  mentioned  for  generating  the 
gas,  others  may  be  used  which  have  the  advantage  to  the  analyst  that  the 
supply  of  gas  may  be  better  regulated.  Fig.  57  shows  such  an  apparatus  for 
the  continuous  preparation  of  the  gas.  It  consists  of  three  glass  bulbs ;  the 
upper  bulb,  prolonged  by  a  tube  reaching  to  the  bottom  of  the  lowest  one,  is 
ground  air-tight  into  the  neck  of  the  second.  Ferrous  sulphide  is  introduced 
into  the  middle  bulb  through  the  tubulure,  which  is  then  closed  by  a  perforated 
cork  through  which  connection  is  made  with  the  wash-bottle.  Acid  poured  in 
through  the  safety  tube,  runs  into  the  bottom  globe  and  rises  to  the  ferrous 
sulphide  in  the  second  bulb.  Upon  closing  the  delivery  tube,  the  pressure  of 
the  generated  gas  forces  the  liquid  from  the  second  bulb  through  the  lower  to 
the  upper,  thus  preventing  contact  of  acid  and  ferrous  sulphide  until  the  gas  is 
used  again. 

A  convenient  and  cheaper  apparatus  is  shown  in  Fig.  58.  A  glass  tube, 
drawn  at  its  lower  end  to  a  small  point  and  partly  filled  with  pieces  of  ferrous 
sulphide,  is  suspended  through  a  cork  (not  air-tight)  in  a  cylinder  containing 
the  acid.  The  gas  supply  is  regulated  by  closing  or  opening  the  stop-cock,  and 
also  by  raising  or  lowering  the  tube  in  the  acid. 


SEPARATION  OF  METALS  INTO  DIFFERENT  GROUPS.      385 


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386  ANALYTICAL   CHEMISTRY. 

In  some  cases  sulphur  is  precipitated  on  the  addition  of  hydrogen 
sulphide,  while  a  change  in  color  may  take  place.  This  change  is 
due  to  the  deoxidizing  action  of  hydrogen  sulphide,  the  hydrogen  of 
this  reagent  becoming  oxidized  and  converted  into  water,  while  sul- 
phur is  liberated.  Thus,  brown  ferric  compounds  are  converted  into 
pale-green  ferrous  compounds;  red  solutions  of  acid  chromates 
become  green;  and  red  permanganates  or  green  manganates  are 
decolorized. 

The  same  deoxidizing  action  of  hydrogen  sulphide  is  the  reason 
why  this  reagent  cannot  be  employed  in  a  solution  containing  free 
nitric  acid,  which  latter  compound  oxidizes  the  hydrogen  sulphide. 

Separation  of  the  metals  of  the  arsenic  from  those  of  the  lead 
group.  The  precipitate  produced  by  hydrogen  sulphide  in  acid  solu- 
tion contains  the  metals  of  the  arsenic  and  lead  groups.  They  are 
separated  by  means  of  ammonium  sulphide,  which  dissolves  the  sul- 
phides of  the  arsenic  group,  but  does  not  act  on  those  of  the  lead 
group. 

Addition  of  ammonium  sulphide.  This  reagent  should  never 
be  added  to  the  acid  solution,  but  the  solution  should  be  previously 
supersaturated  by  ammonium  hydroxide,  as.  otherwise,  a  precipitate 
of  sulphur  may  be  formed.  The  yellow  ammonium  sulphide  is 
almost  invariably  a  polysulphide  of  ammonium,  that  is,  ammonium 
sulphide  which  has  combined  with  one  or  more  atoms  of  sulphur.  If 
an  acid  be  added  to  this  compound,  an  ammonium  salt  is  formed, 
hydrogen  sulphide  is  liberated,  and  sulphur  precipitated : 

(NH4)2S2  +  2HC1  =±=  2NH4C1  -f  H2S  +  S. 

Ammonium  sulphide  precipitates  the  metals  of  the  iron  group  as 
sulphides,  with  the  exception  of  chromium,  which  is  precipitated  as 
hydroxide ;  aluminum  is  precipitated  in  the  same  form  of  combina- 
tion. 

Ammonium  sulphide  (or  ammonium  hydroxide)  causes  also  the 
precipitation  of  metallic  salts  which  have  been  dissolved  in  acids,  as, 
for  instance,  of  the  phosphates,  borates,  silicates,  or  oxalates  of  the 
alkaline  earths,  magnesium,  and  others.  The  processes  by  which  the 
nature  of  some  of  these  precipitates  is  to  be  recognized  are  found  in 
Table  VI.,  page  389. 

Addition  of  ammonium  carbonate.  The  reagent  used  is  the 
commercial  salt,  dissolved  in  water,  to  which  some  ammonia  water 


SEPARATION  OF  THE  METALS  OF  EACH  GROUP.         387 

has  been  added.     Heating  facilitates  complete  precipitation  of  the 
carbonates  of  the  alkaline  earths. 


36.    SEPARATION  OF  THE  METALS  OF  EACH  GROUP. 
TABLE  III.— Treatment  of  the  precipitate  formed  by  hydrochloric  acid. 

The  precipitate  may  contain  silver,  mercurous,  and  lead  chlorides.    Boil 
the  washed  precipitate  with  much  water,  and  filter  while  hot. 


Filtrate  may  contain  lead 
chloride.     Add  dilute 
sulphuric  acid  ;  a  white 
precipitate  of  lead  sul- 
phate is  produced. 

Residue  may  consist  of  mercurous  and  silver  chlor- 
ides.    Digest  residue  with  ammonia  water. 

Solution  may  contain  sil- 
ver.     Neutralize   with 
nitric  acid,  when  silver 
chloride    is    re-precipi- 
tated. 

A  dark    gray  residue  indi- 
cates mercury,  the  white 
mercurous  chloride  having 
been   converted   into    mer- 
curic-ammonium chloride 
and  mercury. 

Treatment  of  the  precipitate  formed  by  hydrogen  sulphide  in 
warm  acid  solution.  The  precipitate  is  collected  upon  a  small 
filter,  well  washed  with  water,  and  then  examined  for  its  solubility 
in  ammonium  sulphide.  This  is  done  by  placing  a  portion  of  the 
washed  precipitate  in  a  test-tube,  adding  ammonium  sulphide,  and 
warming  gently.  It  is  either  wholly  insoluble  (metals  of  the  lead 
group),  and  treated  according  to  Table  IV.,  or  fully  soluble  (metals 
of  the  arsenic  group),  and  treated  according  to  Table  V.,  or  it  is 
partly  soluble  and  partly  insoluble  (metals  of  both  groups).  In  the 
latter  case,  the  total  quantity  of  the  washed  precipitate  is  to  be 
treated  with  warm  ammonium  sulphide;  upon  filtering,  an  insoluble 
residue  is  left,  which  is  treated  according  to  Table  IV. ;  to  the  fil- 

QUESTIONS. — State  the  three  groups  of  heavy,  and  the  three  groups  of  light 
metals.  By  which  two  reagents  may  all  heavy  metals  be  precipitated?  Why 
is  a  solution  acidified  before  the  addition  of  hydrogen  sulphide,  when  testing 
for  metals?  Which  metals  are  precipitated  by  hydrochloric  acid?  Which  two 
groups  of  metals  are  precipitated  by  hydrogen  sulphide  in  acid  solution  ?  How 
are  the  sulphides  of  the  arsenic  group  separated'  from  those  of  the  lead  group? 
Why  is  an  acid  solution  neutralized  or  supersaturated  by  ammonium  hydroxide, 
before  adding  ammonium  sulphide?  Which  two  groups  of  metals  are  precipi- 
tated by  ammonium  sulphide,  and  in  what  forms  of  combination?  Name  the 
group-reagent  for  the  alkaline  earths.  Which  metals  may  be  left  in  solution 
after  hydrogen  sulphide,  ammonium  sulphide,  and  ammonium  carbonate  have 
been  added  ? 


388 


ANALYTICAL   CHEMISTRY. 


trate,  diluted  sulphuric  acid  is  added  as  long  as  a  precipitate  is 
formed,  which  precipitate  contains  the  metals  of  the  arsenic  group  as 
sulphides,  generally  with  some  sulphur  from  the  ammonium  sulphide. 

TABLE  IV.— Treatment  of  that  portion  of  the  hydrogen  sulphide 
precipitate  which  is  insoluble  in  ammonium  sulphide. 

The  precipitate  may  contain  the  sulphides  of  lead,  copper,  mercury, 
bismuth,  and  cadmium.  Heat  the  well-washed  precipitate  with  nitric  acid  in 
a  test-tube,  and  filter. 


Residue    may  con- 
consist  of: 
Mercuric  sulph- 
ide,    which     is 
black  and  easily 
dissolves  in  nitro- 
hydrochloric  acid, 
which      solution, 
after        sufficient 
evaporation,       is 
tested    by    potas- 
sium iodide,  etc. 
Lead  sulphate  is 
white,      pulveru- 
lent, and  soluble 
in    ammonium 
tartrate. 
Sulphur  is  yellow 
and  combustible. 

Filtrate  may  contain  the  nitrates  of  lead,  copper,  bis- 
muth, and  cadmium.     Add  to  the  solution  a  few  drops 
of  dilute  sulphuric  acid. 

Precipitated  is 
lead,  as  white 
lead   sulphate 
which  is  solu- 
ble in  ammo- 
nium   tartrate 
with  excess  of 
ammonium 
hydroxide. 

Solution    may  contain   copper,   bismuth, 
and  cadmium.     Supersaturate  with  am- 
monium hydroxide. 

Precipitated  is 
white    bis- 
muth    hy- 
droxide. 
Dissolve     in 
hydrochloric 
acid  and  ap- 
ply tests  for 
bismuth. 

Solution  may  contain  copper 
and  cadmium 
Divide  solution  in  two   parts, 
and  test  for  copper  by  potas- 
sium   ferrocyanide     in     the 
acidified  solution;  a  red  pre- 
cipitate   indicates   copper. 
To   second   part  add   potas- 
sium   cyanide    and     hydro- 
gen    sulphide.       A    yellow 
precipitate    indicates    cad- 
mium. 

TABLE  V.— Treatment  of  the  hydrogen  sulphide  precipitate  which  is 
soluble  in  ammonium  sulphide. 


The  precipitate  may  contain  the  sulphides  of  arsenic,  antimony,  tin, 
and  a  few  of  those  metals  which  are  but  rarely  met  with  in  qualitative  analysis, 
such  as  gold,  platinum,  molybdenum,  and  others,  which  latter  metals,  if 
suspected,  may  be  detected  by  special  tests. 

Boil  the  washed  precipitate  with  strong  hydrochloric  acid. 


An  insoluble  yellow  residue  consists 
of  arsenous  sulphide 

The  residue  is  dissolved  by  boiling 
with  hydrochloric  acid  and  a  little 
potassium  chlorate,  and  the  solu- 
tion examined  by  Fleitmann's 
test. 

A  dark-colored  residue  may  indi- 
cate gold  or  platinum,  for  which 
use  special  tests. 


The  solution  may  contain  the  chlorides  of 
antimony  and  tin. 

The  solution  is  introduced  into  Marsh's  appara- 
tus when  all  antimony  is  gradually  evolved 
as  antimoniuretted  hydrogen,  while  tin  re 
mains  with  the  undissolved  zinc  as  a  black 
metallic  powder,  which  may  be  collected, 
washed,  dissolved  in  hydrochloric  acid,  and 
the  solution  tested  by  the  special  tests  for 
tin. 


SEPARATION  OF  THE  METALS   OF  EACH  GROUP. 


389 


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390  ANALYTICAL   CHEMISTRY.      . 

The  precipitation  of  sulphur,  in  the  absence  of  metals  of  the  arsenic  group, 
frequently  leads  beginners  to  the  assumption  that  metals  of  this  group  are 
present.  The  precipitate  consisting  only  of  sulphur  is  white  and  milky,  but 
flocculent,  and  more  or  less  colored  in  the  presence  of  the  metals  of  the 
arsenic  group. 

TABLE  VII.— Treatment  of  the  precipitate  formed  by  ammonium 

carbonate. 

The  precipitate  may  contain  the  carbonates  of  barium,  caloium,  and 
Strontium.1  Dissolve  the  precipitate  in  acetic  acid,  and  add  potassium  dichromate. 


Precipitated  is 
barium,  as 
pale  yellow 
barium 

chromate. 

Solution  may  contain  calcium  and   strontium      Neutralize 
solution  with  ammonia  water  and  add  potassium  chromate. 

Precipitated    is    stron- 
tium,  as  pale    yellow 
strontium  chromate. 

Solution  may  contain  calcium     Add 
ammonium  oxalate:  a  white  precipi- 
tate indicates  calcium. 

TABLE  VIII.— Detection  of  the  alkalies  and  of  magnesium. 

The  fluid  which  has  been  treated  with  hydrochloric  acid,  hydrogen  sulphide,  am- 
monium hydroxide,  sulphide,  and  carbonate,  may  contain  magnesium  and  the 
alkalies. 

Divide  solution  into  two  portions. 

To  the  first  portion  add  sodium  phosphate.  A  white  crystalline  precipitate  indi- 
cates magnesium.2 

The  second  portion  is  evaporated  to  dryness,  further  heated  (or  ignited)  until  all 
ammonium  compounds  are  expelled,  and  white  fumes  are  no  longer  given  off.  The 
residue  is  dissolved  in  water,  and  sodium  cobaltic  nitrite  added.  A  yellow  precipitate 
indicates  potassium.  The  residue  is  also  examined  by  flame  test :  a  yellow  color 
indicating  sodium,  a  red  color  lithium. 

Ammonium  compounds  have  to  be  tested  for  in  the  original  fluid  by  treating 
it  with  calcium  hydroxide,  when  ammonia  gas  is  liberated 


1  If  an  insufficient  quantity  of  ammonium  chloride  should  have  been  present,  some  magnesia 
may  also  be  contained  in  this  precipitate,  and  may  be  redissolved  by  treating  it  with  ammonium 
chloride  solution. 

2  If  an  insufficient  quantity  of  ammonium  chloride  has  been  produced  in  the  original  solution 
by  the  addition  of  hydrochloric  acid  and  ammonium  hydroxide,  a  portion  of  the  magnesia  may 
have  been  precipitated  by  the  ammonium  hydroxide  or  carbonate. 


QUESTIONS.— By  what  tests  can  mercurous  chloride  be  distinguished  from 
the  chloride  of  silver  or  lead  ?  How  can  it  be  proved  that  a  precipitate  pro- 
duced by  hydrogen  sulphide  in  an  acid  solution  contains  a  metal  or  metals  of 


DETECTION  OF  ACIDS.  391 


37.    DETECTION  OF  ACIDS. 

General  remarks.  There  are  no  general  methods  (similar  to  those 
for  the  separation  of  metals)  by  which  all  acids  can  be  separated,  first 
into  different  groups,  and  afterward  into  the  individual  acids.  It  is, 
moreover,  impossible  to  render  all  acids  soluble  (when  in  combination 
with  certain  metals)  without  decomposition,  as,  for  instance,  in  the 
case  of  carbonic  acid  when  in  combination  with  calcium ;  calcium 
carbonate  is  insoluble  in  water,  and  when  the  solution  is  attempted 
by  means  of  acids,  decomposition  takes  place  with  liberation  of  carbon 
dioxide.  Many  other  acids  suffer  decomposition  in  a  similar  manner, 
when  attempts  are  made  to  render  soluble  the  substances  in  which 
they  occur. 

It  is  due  to  these  facts  that  a  complete  separation  of  all  acids  is 
not  so  easily  accomplished  as  the  separation  of  metals.  There  is, 
however,  for  each  acid  a  sufficient  number  of  characteristic  tests  by 
which  it  may  be  recognized  ;  moreover,  the  preliminary  examination, 
as  well  as  the  solubility  of  the  substance,  and  the  nature  of  the  metal 
or  metals  present,  will  aid  in  pointing  out  the  acid  or  acids  which 
are  present. 

If,  for  instance,  a  solid  substance  be  completely  soluble  in  water, 
and  if  the  only  metal  found  were  iron,  it  would  be  unnecessary  to 
test  for  carbonic  and  phosphoric  acids  and  hydrogen  sulphide,  because 
the  combinations  of  these  with  iron  are  insoluble  in  water ;  there  might, 
however,  be  present  sulphuric,  hydrochloric,  nitric,  and  many  other 
acids,  which  form  soluble  salts  with  iron. 

Detection  of  acids  by  means  of  the  action  of  strong  sulphuric 
acid  upon  the  dry  substance.  The  action  of  sulphuric  acid  upon 
a  dry  powdered  substance  often  furnishes  such  characteristic  indica- 

either  the  arsenic  or  lead  group?  How  can  mercuric  sulphide  be  separated 
from  the  sulphides  of  copper  and  bismuth?  How  does  ammonium  hydroxide 
act  on  a  solution  containing  bismuth  and  copper  ?  State  the  action  of  strong, 
hot  hydrochloric  acid  on  the  sulphides  of  arsenic  and  antimony.  Suppose  a 
solution  to  contain  salts  of  iron,  aluminum,  zinc,  and  manganese,  by  what 
process  could  these  four  metals  be  separated  and  recognized  ?  How  can  barium, 
calcium,  and  strontium  be  recognized  when  dissolved  together  ?  By  what  tests 
is  magnesium  recognized?  State  a  method  of  separating  potassium  when  mixed 
with  other  metallic  compounds.  How  are  ammonium  compounds  recognized 
when  in  solution  with  other  metals  ? 


392  ANALYTICAL  CHEMISTRY. 

tions  of  the  presence  or  absence  of  certain  acids,  that  this  treatment 
should  never  be  omitted  when  a  search  for  acids  is  made. 

When  the  substance  under  examination  is  liquid,  a  portion  should 
be  evaporated  to  dryness,  and,  if  a  solid  residue  remains,  it  should 
be  treated  in  the  same  manner  as  a  solid. 

Most  non-volatile,  organic  substances  (including  most  organic 
acids)  color  sulphuric  acid  dark  when  heated  with  it. 

Dry  inorganic  salts  when  heated  with  sulphuric  acid  either  are 
decomposed,  with  liberation  of  the  acid  (which  may  escape  in  the 
gaseous  state),  or  with  liberation  of  volatile  products  (produced  by 
the  decomposition  of  the  acid  itself),  or  no  apparent  action  takes 
place.  See  Table  IX. 

Detection  of  acids  by  means  of  reagents  added  to  their 
neutral  or  acid  solution.  Whenever  a  substance  is  soluble  in 
water,  there  is  little  difficulty  of  finding  the  acid  by  means  of  Table 
X. ;  but  if  the  substance  is  insoluble  in  water,  and  has  to  be  rendered 
soluble  by  the  action  of  acids,  this  table  may,  in  some  cases,  be  of  no 
use,  because  the  acid  originally  present  in  the  substance  may  have 
been  liberated,  and  escaped  in  a  gaseous  state  (as,  for  instance,  when 
dissolving  insoluble  carbonates  in  acids),  or  the  tests  mentioned  in 
the  table  may  refer  to  neutral  solutions,  while  it  is  impossible  to 
render  the  solution  neutral  without  re-precipitating  the  dissolved 
acid.  If  calcium  phosphate,  for  instance,  be  dissolved  by  hydro- 
chloric acid,  the  magnesium  test  for  phosphoric  acid  cannot  be  used, 
because  this  test  can  be  applied  to  a  neutral  or  an  alkaline  solution 
only ;  in  attempting,  however,  to  neutralize  the  hydrochloric  acid 
solution,  calcium  phosphate  itself  is  re-precipitated. 

Table  XI.,  showing  the  solubility  or  insolubility  (in  water)  of  over 
300  of  the  most  important  inorganic  salts,  oxides,  and  hydroxides, 
will  greatly  aid  the  student  in  studying  this  important  feature.  It 
will  also  guide  him  in  the  analysis  of  inorganic  substances,  as  it  gives 
directions  for  over  300  (positive  or  negative)  tests  for  metals,  and  an 
equal  number  for  acids. 

To  understand  this,  it  must  be  remembered  that  any  salt  (or  oxide 
or  hydroxide)  which  is  insoluble  in  water  may  be  produced  and  pre- 
cipitated by  mixing  two  solutions,  one  containing  the  metal,  the  other 
containing  the  acid  of  the  insoluble  salt  to  be  formed.  For  instance  : 
Table  XI.  states  that  the  carbonates  of  most  metals  are  insoluble  in 
water.  To  produce,  therefore,  the  carbonate  of  any  of  these  metals 
(zinc,  for  instance)  it  becomes  necessary  to  add  to  any  solution  of 


DETECTION  OF  ACIDS.  393 

zinc  (sulphate,  chloride,  or  nitrate  of  zinc)  any  soluble  carbonate 
(sodium  or  potassium  carbonate),  when  the  insoluble  zinc  carbonate 
is  produced. 

Soluble  carbonates  consequently  are  reagents  for  soluble  zinc  salts, 
while  at  the  same  time  soluble  zinc  salts  are  reagents  for  soluble 
carbonates. 

For  similar  reasons  soluble  zinc  salts  are,  according  to  Table  XI., 
reagents  for  soluble  phosphates,  arsenates,  arsenites,  hydroxides,  and 
sulphides,  but  not  for  iodides,  chlorides,  sulphates,  nitrates,  or 
chlorates. 

The  insolubility  of  a  compound  in  water  is  not  an  absolute  guide 
for  preparing  this  compound  according  to  the  general  rule  given 
above  for  the  precipitation  of  insoluble  compounds,  there  being  some 
exceptions. 

For  instance  :  Cupric  hydroxide  is  insoluble  in  water  ;  therefore, 
by  adding  solution  of  cupric  sulphate  to  any  soluble  hydroxide,  the 
insoluble  cupric  hydroxide  should  be  precipitated,  and  is  precipitated 
by  the  soluble  hydroxides  of  potassium  and  sodium,  but  not  perma- 
nently by  the  soluble  hydroxide  of  ammonium,  on  account  of  the 
formation  of  the  soluble  ammonium  cupric  sulphate. 

There  are  not  many  such  exceptions,  and  to  mention  them  in  the 
table  would  have  greatly  interfered  with  its  simplicity,  for  which 
reason  they  have  been  omitted. 

For  the  same  reason  some  compounds,  which  are  not  known  at  all, 
have  not  been  specially  mentioned.  For  instance,  according  to  Table 
XI.,  aluminum  carbonate  and  chromium  carbonate  are  insoluble  salts  : 
actually,  however,  these  compounds  can  scarcely  be  formed,  the 
affinity  between  the  weak  carbonic  acid  and  the  feeble  bases  not 
being  sufficient  to  unite  them.  Also,  bismuth  nitrate  and  a  lew 
other  salts  are  reported  as  soluble,  while  actually  they  suffer  a 
decomposition  by  water. 

Finally,  it  may  be  stated  that  no  well-defined  line  can  be  drawn 
between  soluble  and  insoluble  substances.  There  is  scarcely  any 
substance  which  is  not  slightly  soluble  in  water,  and  many  of  the 
so-called  soluble  substances  are  but  very  sparingly  soluble,  as,  for 
instance,  the  hydroxide  and  sulphate  of  calcium. 

Table  XII.  shows  the  solubility  of  a  large  number  of  compounds 
more  accurately  than  Table  XL ;  it  may  be  used  for  reference. 


394 


ANALYTICAL  CHEMISTRY. 


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DETECTION  OF  ACIDS. 


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396 


ANALYTICAL   CHEMISTRY. 


Table  XI. 


Systematically  arranged  table  showing  the  solubility  and 
insolubility  of  inorganic  salts  and  oxides  in  water. 

The  dark  squares  represent  insoluble,  the  white  soluble  compounds. 


Ca 


Potassium 


Sodium 


Ammonium 


M 


Calcium 


Barium 


Strontium 


Magnesium 


Aluminum 


Ferric 


Ferrous 


Zinc 


Chromium 


Nickel 


Cobalt 


Manganese 


Stannic 


Stannous 


Arsenic 


Arsenous 


Antimony 


Gold 


Platinum 


Copper 


Bismuth 


Cadmium 


Mercuric 


Mercurous 


Silver. 


Lead, 


O 


DETECTION  OF  ACIDS. 


397 


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ALUMINUM. 


AMMONIUM. 


ANTIMONY. 


BARIUM. 


BISMUTH. 


CADMIUM. 


CALCIUM. 


CHROMIUM. 


COBALT. 


COPPKR. 


FERROUS. 


FERRIC. 


LEAD. 


MAGNESIUM. 


MANGANESE. 


MERCUROUS. 


MERCURIC. 


NICKEL. 


POTASSIUM. 


STRONTIUM 


ZINC. 


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398  ANALYTICAL   CHEMISTRY. 

Special  remarks.  Often  a  solution  is  presented  for  analysis  instead  of  a 
solid  substance,  in  which  case  some  of  it  is  evaporated  to  dryness.  If  a  dry 
residue  is  left,  this  is  tested  for  acids,  as  already  described.  But  no  residue  may 
remain,  and  if  the  solution  has  a  strongly  acid  reaction,  the  presence  of  the 
volatile  acids  is  indicated,  and  the  student,  guided  by  the  odor  and  change  of 
color  upon  evaporation,  should  make  tests  for  the  following  acids:  hydro- 
chloric, hydrobromic,  hydriodic,  nitric,  sulphurous  (hydrocyanic,  acetic, 
formic). 

If  a  strongly  acid,  fuming,  oily  residue  is  left,  sulphuric  acid  is  indicated. 

A  strongly  acid,  pasty,  non-fuming  residue  indicates  phosphoric  acid. 

If  the  solution  is  strongly  acid  and  leaves  a  solid  residue,  the  substance  may 
be  either  an  acid  salt,  or  a  salt  held  in  solution  by  an  acid,  such  as  hydrochloric, 
nitric,  sulphuric,  etc.,  in  which  case  several  acids  would  have  to  be  looked  for. 
The  presence  of  the  volatile  acids  would  be  indicated  by  holding  wet  blue 
litmus-paper  in  the  vapor  as  the  liquid  approached  high  concentration.  If  the 
residue  upon  evaporation  is  decidedly  alkaline,  this  maybe  due  to  a  salt  having 
an  alkaline  reaction,  or  to  a  hydroxide,  or  both.  The  presence  of  a  hydroxide 
is  shown  by  adding  some  solution  of  silver  nitrate  to  the  diluted  solution,  when 
a  dark  precipitate  of  silver  oxide  is  formed  at  once.  In  the  absence  of  carbon- 
ate, the  presence  of  hydroxide  is  also  shown  by  adding  some  dry  ammonium 
chloride  to  the  solution  and  warming,  when  ammonia  is  liberated.  A  solution 
containing  a  hydroxide  must,  of  course,  be  neutralized  before  applying  the  tests 
for  acids.  The  acid  usually  employed  for  this  is  dilute  nitric,  but  if  tests  are 
also  to  be  made  for  the  latter  acid,  another  portion  of  the  solution  is  neutralized 
with  hydrochloric  or  acetic  acid. 

A  solution  may  be  colorless,  odorless,  practically  neutral,  leave  no  residue 
upon  evaporation,  and  still  not  be  plain  water.  In  such  a  case,  the  student  may 
suspect  hydrogen  dioxide.  He  would  have  reason  to  suspect  this  compound  if 
he  proceeded  to  search  for  metals  before  evaporating  and  found  none,  but  got  a 
precipitate  of  sulphur  when  using  hydrogen  sulphide,  showing  an  oxidizing 
action. 

The  presence  of  some  metals  interferes  with  certain  tests  for  acids,  and  these 
should  be  removed.  After  determining  the  kind  of  metal  or  metals  in  a  sub- 
stance or  a  mixture,  and  it  is  seen  that  there  will  be  interference  with  the  tests 
for  acids,  boil  some  of  the  substance  with  a  slight  excess  of  sodium  or  potassium 
carbonate  for  some  time  and  filter.  Non-alkali  metals,  except  arsenic  and 
antimony,  remain  behind,  while  the  acids  pass  into  the  filtrate  as  alkali  salts 
(with  few  exceptions).  The  filtrate  is  then  exactly  neutralized  with  nitric  acid 
and  boiled  to  expel  all  carbonic  acid,  and  used  for  the  various  tests  for  acids. 
Arsenic  and  antimony  may  be  removed  by  passing  hydrogen  sulphide  into  the 
warm  acidified  solution  and  filtering. 

Substances  insoluble  in  water.  When  a  single  substance,  or  that  part  of  a 
mixture  which  is  insoluble  in  water,  is  treated  with  hydrochloric  acid  in  order 
to  prepare  a  solution  for  the  analysis  of  metals,  something  can  be  learned  as  to 
the  nature  of  the  acids  in  combination.  Carbonates,  sulphites,  phosphates, 
arsenates,  and  arsenites  behave  the  same  as  when  treated  with  concentrated 
sulphuric  acid  in  Table  IX.  Sulphides  give  the  odor  of  hydrogen  sulphide.  If 
chlorine  gas  is  given  oif,  the  presence  of  a  higher  oxide,  like  MnO2,  PbO2,  BaO2, 
etc.,  or  a  chromate  is  indicated.  If  effervescence  takes  place  and  an  inflamma- 


DETECTION  OF  ACIDS.  399 

ble  gas  is  given  off,  the  presence  of  a  free  metal  is  indicated.  If  the  substance 
simply  dissolves  and  no  acids  are  subsequently  found,  the  presence  of  an  oxide 
or  hydroxide  is  indicated,  which  can  also  be  judged  from  a  knowledge  of  the 
known  compounds  of  the  metals  present. 

The  tests  distinguishing  between  an  arsenite  and  an  arsenate  (see  Chapter  on 
Arsenic)  cannot  be  applied  when  the  substance  is  insoluble  in  water  (except  the 
inolybdate  test,  which  can  be  used  in  an  acid  solution),  but  the  treatment  with 
hydrogen  sulphide  can  be  used  to  differentiate,  because  an  arsenite  gives  a  pre- 
cipitate instantly  even  in  cold  solution,  while  an  arsenate  precipitates  only  after 
a  long  time. 

If  bismuth  is  present,  remove  it  before  testing  for  the  acids  by  boiling  with 
sodium  carbonate,  filtering,  etc.,  as  described  above. 

Substances  insoluble  in  water  and  hydrochloric  acid  are  next  treated  with 
nitric  acid.  Ordinarily  very  few  such  substances  are  presented.  If  brown 
vapors  are  evolved  and  sulphur  separates,  a  sulphide  is  indicated,  which  the 
appearance  of  the  substance  will  also  suggest.  If  brown  vapors  alone  are 
evolved,  a  free  metal  is  indicated. 

If  the  preliminary  tests  for  metals  show  the  presence  of  mercury,  and  the 
substance  dissolves  slowly  on  boiling  with  nitric  acid,  it  is  one  of  the  halogen 
salts.  The  mercury  should  be  removed  by  boiling  the  substance  with  an  excess 
of  caustic  alkali,  filtering,  neutralizing  the  filtrate  with  nitric  acid,  and  testing 
it  for  chloride,  bromide,  or  iodide. 

Before  examining  for  metals,  nitric  acid  solutions  must  be  evaporated  to  dry- 
ness  to  expel  excess  of  the  acid.  The  residue  is  dissolved  in  water. 

A  few  substances  require  nitro-hydrochloric  acid  for  solution.  The  one  most 
likely  to  occur  ordinarily  is  mercuric  sulphide,  which  is  indicated  by  the  pres- 
ence of  mercury,  its  black  or  vermilion  color,  and  volatility  on  heating. 

Of  substances  insoluble  in  all  acids,  the  sulphates  of  barium,  strontium,  and 
lead  are  the  most  likely  to  be  presented  ordinarily.  The  treatment  of  these  by 
fusion  with  sodium  carbonate  has  already  been  mentioned.  The  presence  of 
silver  (as  shown  by  the  preliminary  tests  for  metals)  would  indicate  a  chloride, 
bromide,  iodide,  or  cyanide  of  this  metal.  The  metal  should  be  removed  by 
boiling  with  caustic  alkali  and  the  filtrate  tested.  Silver  iodide  does  not  yield 
to  this  treatment,  but  its  color  and  insolubility  in  strong  ammonia  is  sufficient 
evidence  of  iodide.  Silver  cyanide  with  hydrochloric  acid  forms  silver  chloride 
and  hydrocyanic  acid,  which  is  in  solution  and  recognized  by  its  odor. 

The  insoluble  halogen  salts  of  silver,  lead,  and  mercury,  also  mercuric  chloride 
and  bromide,  scarcely  react  when  treated  with  concentrated  sulphuric  acid 
(Table  IX). 

Most  of  the  points  in  the  discussion  above  are  shown  in  more  convenient 
form  in  the  following  Tables,  XIII  and  XIV,  which  are  more  detailed  than  Table 
IX,  and  will  perhaps  be  of  greater  help  to  the  student.  Table  XIV  deals  with 
difficultly  soluble  or  insoluble  substances,  which  may  be  subnitrate ;  subchlor- 
ide;  chloride  (Pb,  Hg(ous),Ag) ;  bromide  (Pb,  Hg(ous),Ag) ;  iodide;  sulphate 
(Ca,  Sr,  Ba,  Pb,  Hg(ous) ;  sulphite  (except  of  alkalies) ;  sulphide  (except  of 
alkalies  and  alkaline  earths) ;  carbonate,  borate,  phosphate,  arsenate,  arsenite 
(except  of  alkalies  in  each  case);  chromate  (high  color) ;  fluoride;  cyanide; 
oxide  or  hydroxide  (except  of  alkali  and  alkaline  earth  metals) ;  and  a  few 
others. 

In  the  case  of  mixtures,,  the  tables  may  be  used  to  determine  as  far  as 


400 


ANALYTICAL   CHEMISTRY. 


possible  the  nature  of  the  acids,  after  which  such  other  acids  must  be 
looked  for  as  are  not  clearly  indicated  by  the  tables,  but  may  be  suggested 
as  probably  present  by  the  preliminary  examinations  and  the  nature  of  the 
metals  found. 


TABLE  XIII.— Substances  soluble  in  water. 


A.  When  the  substance  is 
already  in  solution,  test  with 
litmus  paper  and  evaporate 
20  c.c.  to  dryness  : 

B.   When  the  substance  is  ir 
to  litmus  paper  and  — 

I.   Warm  a  little  with  di- 
lute sulphuric  acid  : 

\,  the  dry  state,  test  its  reaction 

II.  If  I  gives  no  indication, 
heat  moderately  a  small  quan- 

tny  with  concentrated  sul- 
phuric acid. 

strongly   acid   and 

HC1,  HBr,  HI,  HNO3, 
HCN*  or  H2SO3.  Note 
odor  of  vapors  and  test  for 
the  acid  indicated  by  odor, 
etc. 

a.  Copious  effervescence, 
no  color   or  odor  —  test    for 
carbonate    (strongly    alka- 
line) or  bicarbonate  (weakly 
alkaline). 

a.  White  fumes  —  test  for 
HC1,  HF  or  HN03.  Note 
odor.  The  salt  is  neutral 
or  slightly  acid. 

L    (-1  -i      j  f 

6.  A  strongly  acid,  fum- 
ing residue  —  test  for  free 
H2S04. 

b.  Moderate    efferves- 
cence. TIO  color,  but  with  an 
1.  Odor  of  SO2    test  for 

1.  Brownish  —  test  for 
bromide. 
2.  V  i  o  1  e  t  —  test    for 
iodide. 

c.  A  strongly  acid,  soft, 
non-fuminq  mass  —  test  for 
free  H3PO4. 

sulphite  (alkaline). 
Odor  of    SO2  -j-  precipi- 
tate   of    sulphur  —  test    for 
thiosulphate   (neutral). 

3.   Greenish  -yellow  —  test 
for  chlorate. 
(Bromates   and    iodates, 
like    chlorates,    also    give 

d.  A  strongly  acid,  com- 
bustible mass  —  test  for  free 

A.  \JQOT  ot  ±i2o  —  test  lor 
a  sulphide  (alkaline). 
3.  Odor  of  HCN*—  test 

colored  fumes  and  defla- 
grate on  charcoal.) 

H3PO2:  a  neutral  combus- 
tible mass,  indicates  a  salt 
of  H3PO2  (hypophosphor- 
ous  acid). 

for  cyanide  (alkaline). 
4.  Odor  of  HCN  and  a 
cryst.  deposit,  often  bluish 
—  test   for   ferro-  or    ferri- 
cyanide. 

c.  Chromates  and  dichro- 
mates  are  recognized  by 
their  color  and  give  green 
solutions  in  hot  concen- 

e.  Strongly  acid,  leaving 

5.  Odor  of  HCN  -f  ppt. 
of  sulphur  —  test  for  a  sul- 

trated  H2SO4. 

a  solid  residue  —  it  may  be 
an  acid  salt  or  a  salt  held 
in  solution  by  an  acid,  as 

phocyanate. 

d.  No  change  takes  place. 
It  may  be  sulphate  (neu- 

HC1, HN03,  H2S04,  etc. 
Refer  to  B. 

c.  Colored  fumes. 

tral  or  slightly  acid),  phos- 
phate (alkaline),  arsenate 
or  arsenite  (alkaline),  bo- 

f.  A  slightly  acid  white 
residue  which  melts  at  high 
heat  —  test  for  free  boric 
acid. 

trite  (alkaline). 
2.  Greenish,    with    odor 
of  Cl  —  test  for  hypochlorite 
(alkaline). 

rate  (alkaline),  boric  acid, 
or  a  free  base.  All  these 
acids  would  be  indicated  in 
the  preliminary  examina- 
tions and  the  analysis  for 
the  metals.  If  the  sub- 

g. A  weakly  acid,  neu- 
tral, or  alkaline  residue  — 
it  may  be  a  salt  or  a  free 
base,  or  both.  Refer  to  B. 

*  Caution.  —  Take  care  in 
smelling   vapors   of    HCN, 
as  they  are  poisonous. 

stance  is  alkaline  and  gives 
a  precipitate  (dark)  with 
solution  of  AgNO3,  a  free 
base  is  present.  Test  also 
on  NH4C1. 

DETECTION  OF 'ACIDS.  401 

TABLE  XIV.— Substances  insoluble  or  very  difficultly  soluble  in  water. 


A.  When  the  substance  is 
soluble  in  cold  or  hot,  dilute 
or  strong  hydrochloric  acid: 

Note.— It  Pb,  Hg(ous), 
Ag,  are  indicated  by  the 
preliminary  examination, 
omit  treatment  with  HC1, 
but  use  HNO3. 


«.  Note  whether  the 
effects  are  the  same  as  in 
Table  XIII,  B,  7,  a  and  b. 
Make  tests  for  the  acids 
indicated  there. 


b.  If  chlorine  is  given 
off,  a  peroxide  is  present, 
as  MnO2,  PbO?,  BaO2,  etc., 
or  chromate  (high  color) . 


c.  If    no    change     takes 
place  except  solution — 

1.  Subnitrate    (or    sub- 
chloride)  is  suspected  if  Bi 
or   Sb   is   found    as   metal. 
Boil  substance  in  slight  ex- 
cess Na2COs,  filter,  neutral- 
ize filtrate  and  test  for  the 
acid. 

2.  Test  for  phosphate  by 
molybdate  solution. 

3.  Test  for  borate  by  al- 
cohol flame. 

4.  Arsenate  and  arsenite 
are  detected  in  analysis  for 
metals:  make  further  tests 
to  distinguish  the  two. 

5.  If   no    acid   is   found 
and  the  substance  is  alka- 
line, it  is  CaO  or  Ca(OH)2 ; 
if  neutral,  it  is  an  oxide,  as 
ZnO,    MgO,    PbO,  etc.,  or 
their  hydroxides. 


d.  Effervescence  and  in- 
flammable gas — indicate  a 
free  metal,  as  Zn,  Fe,  Sn, 
etc. 


7>.  When  the  substance  is 
insoluble  or  difficultly  soluble 
in  hydrochloric,  but  soluble  in 
cold  or  hot,  dilute  or  strong 
nitric  acid : 


a.  Brown  vapors  and  a 
precipitate  of  sulphur  indi- 
cate a  sulphide. 


6.  Brown  vapors  alone 
indicate  free  metal,  as  Ag, 
Pb,  Hg,  Bi,  Cu,  etc. 


c.  If  the  substance  is 
white,  volatile  on  foil  by 
heat,  turns  black  with 
XII4OH,  and  soluble  in 
HNO3  on  long  boiling,  it 
is  likely  HgCl  or  HgBr. 
Test  for  the  acid  by  boiling 
some  with  dilute  NaOH, 
filter,  acidify  filtrate  with 
HNOS  and  add  AgNO3. 

(Likewise  for  Hgl  and 
HgI2,  which  are  yellow  and 
red  respectively.) 


d.  If  no  change  except 
solution,  the  substance  is 
likely  an  oxide  or  hydrox- 
ide. This  will  also  be  indi- 
cated by  the  metal  present 
and  the  appearance  of  the 
compound. 


C.  When  the  substance  is 
insoluble  in  either  hydro- 
chloric or  nitric,  but  is  solu- 
ble in  a  mixture  of  the  acids  : 


It  may  be — 

a.  Mercuric  sulphide, 
HgS,    black    or    red,    and 
volatile  on  foil  by  heat. 

b.  Gold. 

c.  Mercurous      chloride, 
HgCl.     (Slowly  soluble  in 
HNO3.     See  E,  c.} 

d.  A  few  sulphides  and 
oxides. 


D.  When  the  substance  is 
insoluble  in  all  acids  : 


It  may  be — 

a.  Sulphate  of  Ba,  Sr, 
Pb.  These  must  be  fused 
with  Na2CO3. 

6.  Lead  chloride,  PbCl2 
(PbBr2,  PbI2)  (if  not  re- 
moved by  much  hot  water.) 

c.  Chloride,  bromide, 
iodide,  or  cyanide  of  silver, 
AgCl,  AgBr,   Agl,   AgCN. 
Test  solubility  in  XH4OH 
and  Na2S2O3. 

(AgCN  with  HC1  forms 
insoluble  AgCl  and  leaves 
HCN  in  solution  recognized 
by  odor.) 

d.  Silicic  acid  and  most 
silicates,  native  A12OH, 
Cr2O3,  SnO2,  CaF2. 


402  ANALYTICAL  CHEMISTRY. 

38.    METHODS  FOR  QUANTITATIVE   DETERMINATIONS. 

General  remarks.  Quantitative  determination  of  the  different 
elements  or  groups  of  elements  may  be  accomplished  by  various 
methods,  which  differ  generally  with  the  nature  of  the  substance  to 
be  examined.  But  even  one  and  the  same  substance  may  often  be 
analyzed  quantitatively  by  entirely  different  methods,  of  which  the 
two  principal  ones  are  the  gravimetric  and  volumetric  methods. 

In  the  gravimetric  method,  the  quantities  of  the  constituents  of  a 
substance  are  determined  by  separating  and  weighing  them  either  as 
such,  or  in  the  form  of  some  compound  the  exact  composition  of 
which  is  known.  For  instance :  From  cupric  sulphate,  the  copper 
may  be  precipitated  as  such  by  electrolysis  and  weighed  as  metallic 
copper,  or  it  may  be  precipitated  by  sodium  hydroxide  as  cupric  oxide, 
CuO,  and  weighed  as  such.  Knowing  that  every  79.6  parts  by  weight 
of  cupric  oxide  contain  of  oxygen  16  parts  and  of  copper  63.6  parts, 
the  weight  of  copper  contained  in  the  cupric  oxide  found  may  be 
readily  calculated. 

In  the  volumetric  method,  the  determination  is  accomplished  by  add- 
ing to  a  weighed  quantity  of  the  substance  to  be  examined,  a  solution 
of  a  reagent  of  a  known  strength  until  the  reaction  is  just  completed, 
no  excess  being  allowed.  For  instance  :  We  know  that  every  80.12 
parts  by  weight  of  sodium  hydroxide  precipitate  79.6  parts  by  weight 
of  cupric  oxide,  containing  63.6  parts  by  weight  of  copper.  There- 
fore, if  we  add  a  solution  of  sodium  hydroxide  of  known  strength  to  a 
weighed  portion  of  cupric  sulphate  until  all  the  copper  is  precipitated, 

QUESTIONS. — Why  is  sulphuric  acid  added  to  a  solid  substance  when  it  is  to 
be  examined  for  acids  ?  Mention  some  acids  which  cause  the  liberation  of 
colorless,  and  some  which  cause  the  liberation  of  colored  gases  when  the  salts 
of  these  acids  are  heated  with  sulphuric  acid.  Mention  an  acid  which  is  pre- 
cipitated by  barium  chloride  in  acid  solution,  and  some  acids  which  are  pre- 
cipitated by  the  same  reagent  in  neutral  solution.  Which  acids  may  be  pre- 
cipitated by  silver  nitrate  from  neutral  solutions,  and  which  from  either  neutral 
or  acid  solutions?  Mention  some  acids  which  form  soluble  salts  only.  Mention 
three  soluble,  and  three  insoluble  carbonates,  phosphates,  arsenates,  sulphates, 
and  sulphides  respectively.  Which  oxides  or  hydroxides  are  soluble,  and 
which  are  insoluble  in  water?  Mention  some  metals  the  solutions  of  which 
are  precipitated  by  soluble  chlorides,  iodides,  and  sulphides.  State  a  general 
rule  according  to  which  most  insoluble  salts  may  be  formed  from  two  other 
compounds.  Why  is  it  sometimes  impossible  to  render  a  substance  soluble  in 
order  to  test  for  the  acid  in  the  solution  obtained  ? 


METHODS  FOR   QUANTITATIVE  DETERMINATIONS.        403 

we  may  calculate  from  the  volume  of  soda  solution  used  the  weight  of 
sodium  hydroxide,  and  from  this  the  weight  of  copper  which  has  been 
precipitated.  The  operation  of  volumetric  analysis  is  termed  titration. 

Gravimetric  methods.  While  the  quantitative  determinations  by 
these  methods  differ  widely  in  some  cases,  there  are  a  number  of  oper- 
ations so  often  and  so  generally  employed  that  a  few  remarks  may  be 
of  advantage  to  the  beginner.  A  small  quantity  (generally  from  0.5 
to  1  gramme)  of  the  substance  to  be  analyzed  is  very  exactly  weighed 
on  a  delicate  balance,  transferred  to  a  beaker,  and  dissolved  in  a  suit- 
able agent  (\vater  or  acid).  From  this  solution  the  constituent  to  be 

FIG.  59. 


Drying-oven. 

determined  is  precipitated  completely,  which  is  ascertained  by  allow- 
ing the  precipitate  to  subside  and  adding  to  the  clear  liquid  a  few 
drops  more  of  the  agent  used  for  precipitation.  The,  precipitate  is 
next  collected  upon  a  small  filter  of  good  filter  paper  containing  as 
little  of  inorganic  constituents  (ash)  as  possible ;  the  particles  of  pre- 
cipitate which  may  adhere  to  the  beaker  are  carefully  washed  off  by 
means  of  a  camelVhair  brush.  The  precipitate  is  well  washed  (gen- 
erally with  pure  water)  until  free  from  adhering  solution,  and  dried 
by  placing  funnel  and  contents  in  a  drying- oven,  Fig.  59,  in  which  a 
constant  temperature  of  about  100°  C.  (212°  F.)  is  maintained.  The 
dried  filter  is  then  taken  from  the  funnel  and  its  contents  are  trans- 
ferred to  a  platinum  (or  porcelain)  crucible,  which  has  been  previously 


404 


ANALYTICAL   CHEMISTRY. 


weighed  and  stands  on  a  piece  of  glazed,  colored  paper  in  order  to 
collect  any  particle  of  the  dried  precipitate  which  may  happen  to  fall 
beside  the  crucible.  The  filter,  from  which  the  precipitate  has  been 
removed  as  completely  as  possible,  by  slightly  rubbing  it,  is  now 
folded,  placed  upon  the  lid  of  the  crucible,  which  rests  on  a  triangle 
over  a  gas  burner,  and  completely  incinerated.  The  remaining  filter- 
ash,  with  particles  of  the  precipitate  mixed  with  it,  is  transferred  to 
the  crucible,  which  is  now  placed  over  the  burner  and  heated  until 
all  water  (or  possibly  other  substances)  is  completely  expelled.  After 
cooling,  the  crucible  is  weighed,  the  weight  of  the  empty  crucible  and 
that  of  the  filter-ash  (the  latter  having  been  previously  determined 
by  burning  a  few  filters  of  the  same  kind)  deducted,  and  thus  the 
quantity  of  the  precipitate  determined. 

As  platinum  crucibles  and  many  precipitates,  after  ignition,  absorb 
moisture  from  the  air,  it  is  well  to  allow  the  heated  crucible  to  cool 
in  a  desiccator.  This  is  a  closed  vessel  in  which  the  contained  air  is 
kept  dry  by  means  of  concentrated  sulphuric  acid.  Fig.  60  shows  a 
convenient  form  of  desiccator. 

The  empty  crucibles  should  be  weighed  under  the  same  conditions 
— i.  e.,  after  having  been  heated  and  cooled  in  a  desiccator. 


FIG.  60. 


FIG.  61. 


Desiccator. 


Watch-glasses  for  weighing  filters. 


Some  precipitates  (as,  for  instance,  potassium  platinic  chloride), 
cannot  be  ignited  without  suffering  partial  or  complete  decomposition. 
It  is  for  this  reason  that  some  precipitates  are  collected  upon  filters 
which  have  been  previously  dried  at  100°  C.  (212°  F.)  and  weighed 
carefully.  The  precipitate  is  then  collected  upon  the  weighed  filter, 
well  washed,  dried  at  100°  C.  (212°  F.)  and  weighed. 

The  weighing  of  dried  filters  is  best  accomplished  by  placing  them 


METHODS  FOR   QUANTITATIVE  DETERMINATIONS.        405 

between  two  watch-glasses  held  together  by  means  of  a  brass  or  nickel 
clamp,  as  shown  in  Fig.  61. 

The  above-described  methods  may  be  employed  for  the  determina- 
tion of  those  substances  which  can  be  precipitated  from  their  solu- 
tions in  the  form  of  some  stable  compound.  Aluminum,  zinc,  iron, 
bismuth,  copper,  etc.,  may,  for  instance,  be  precipitated  as  hydroxides 
and  weighed  as  oxides,  into  which  the  precipitated  compound  is  con- 
verted by  ignition.  Sulphuric  acid  may  be  precipitated  and  weighed 
as  barium  sulphate,  phosphoric  acid  may  be  precipitated  by  magnesia 
mixture  and  weighed  as  magnesium  pyrophosphate,  etc.  Some  sub- 
stances, like  nitric  acid,  chloric  acid,  etc.,  cannot  be  precipitated  from 
their  solutions,  for  which  reason  other  methods  have  to  be  employed 

for  their  determination. 

FIG.  63. 


FIG.  62. 


10  CO 


Liter  flask. 


Pipettes. 


406  ANALYTICAL  CHEMISTRY. 

Volumetric  methods.  The  great  advantage  of  volumetric  over 
gravimetric  analysis  consists  chiefly  in  the  rapidity  with  which  these 
determinations  are  performed.  Unfortunately,  volumetric  methods 
cannot  be  employed  to  advantage  for  the  estimation  of  all  substances. 

The  special  apparatus  required  for  volumetric  analysis  consists  of 
a  few  flasks,  some  pipettes,  burettes,  and  a  burette-holder.  The  flasks 
should  have  a  mark  on  the  neck,  indicating  a  capacity  of  100,  250, 
500,  and  1000  c.c.  respectively.  (See  Fig.  62.) 

FIG.  64.  FIG.  65. 


Mohr'8  burette  and  clamp.  Mohr,g  burette  and  hoMer 


Of  pipettes  (Fig.  63)  are  mostly  used  those  having  a  capacity  of 
5,  10,  25,  and  50  cubic  centimeters. 

Of  burettes  many  different  forms  are  used;  in  most  cases  Mohr's 
burette  (Pigs.  64  and  65)  answers  all  requirements,  but  its  applica-  • 


METHODS  FOR   QUANTITATIVE  DETERMINATIONS.        407 

tion  is  excluded  whenever  the  test  solution  is  chemically  affected  by 
rubber,  as  in  the  case  of  solutions  of  silver,  permanganate,  and  a  few 
other  substances.  For  such  solutions  pIQ  66 

Mohr*s  burette  with  glass  stopcock,  or 
Gay  Lussac's  burette  (Fig.  66)  is  generally 
used. 

Standard  solutions  are  solutions  con- 
taining a  known  and  definite  quantity  of 
some  reagent  employed  in  volumetric 
analysis.  A  standard  solution  may  be 
normal,  or  it  may  be  an  empirical  solu- 
tion. In  the  latter  case  it  contains  in 
a  liter  some  arbitrarily  chosen  weight  of 
reagent.  As  an  instance  may  be  men- 
tioned Fehling's  solution,  used  for  the 
determination  of  sugar.  This  solution 
is  so  adjusted  that  1  c.c.  decomposes  or 
indicates  0.005  gm.  of  grape-sugar. 

Normal  solutions.  The  solutions  gen- 
erally used  in  volumetric  analysis  are 
known  as  normal  solutions,  and  are 
chemically  equivalent  to  each  other  be- 
cause of  the  standard  adopted  in  their 
preparation.  This  standard  is  one  gm. 
of  hydrogen,  or  the  weight  of  one  atom 
of  hydrogen  expressed  in  grammes,  or 
the  chemical  equivalent  of  one  gm,  of 
hydrogen,  contained  in  one  liter  of  solu- 
tion. For  the  sake  of  convenience  the  terms 
gram-atom  and  gram-molecule  are  often 
used  in  connection  with  volumetric  work,  Gay  Lussac's  burette. 
and  refer,  of  course,  to  the  atomic  or  molecular  weight  of  the  substance 
considered,  expressed  in  grammes. 

A  consideration  of  the  application  of  these  principles  to  practical  work  is 
volumetric  analysis  may  assist  the  student  in  understanding  them  fully. 

Thus,  a  normal  add  solution  may  be  defined  as  one  containing  in  a  liter 
as  much  acid  as  contains  one  gram-atom  of  replaceable  hydrogen.  In  such 
acids  as  HC1,  HBr,  HN03,  a  liter  solution  containing  the  gram-molecule  would 
be  normal,  since  each  solution  would  contain  one  gram-atom  of  replaceable 
hydrogen.  In  order  to  make  a  normal  solution  of  such  acids  as  H2SO4,  H2C2O4, 


408  ANALYTICAL  CHEMISTRY. 

one-half  the  gram-molecule  must  be  taken,  since  this  quantity  contains  one 
atom  of  hydrogen,  and  so  on. 

A  normal  alkali  solution  may  be  defined  as  one  containing  that  quantity  of 
alkali  in  a  liter  which  is  chemically  equivalent  to—  i.  e.,  neutralizes^  one  gram- 
atom  of  acid  hydrogen.  For  such  compounds  as  KOH,  NaOH,  NH4OH,  the 
whole  gram-molecule  must  be  taken  to  make  a  liter  of  normal  solution.  In 
case  of  Ba(OH)2  or  Ca(OH)2,  one  half  the  gram-molecule  is  taken. 

It  will  easily  be  seen  that  all  the  acid  solutions  made  as  described  are  of 
equivalent  strength  and  are  exactly  equivalent  to  the  solutions  of  alkali—  i.  e.,  one 
liter  normal  HC1  will  exactly  neutralize  one  liter  of  normal  KOH,  or  NaOH, 
or  Ba(OH)2.  That  this  is  so  will  appear  at  once  on  writing  the  equations 
which  express  the  reactions  between  these  alkalies  and  acids,  thus: 

HC1  +  KOH  =  KC1  +  H2O. 
36.18        55.74 

2HC1  +  Ba(OH)2  =  BaCl2  +  2H2O. 


36.18 

L 

KOH  +   H2SO*  =  K£O*-  +  H2O. 
55,4         ^ 

The  above  equations  show  that  36.18  gramme  of  HC1  are  equivalent  to 
55.74  gramme  of  KOH,  but  these  are  the  quantities  taken  for  a  liter  of  normal 
solution  respectively,  hence  these  normal  solutions  must  be  equivalent.  Simi- 
larly for  HC1  and  Ba(OH)2,  for  KOH  and  H2SO4,  etc. 

Conversely,  if  a  solution  of  unknown  strength  be  compared  by  titration  with 
a  second  solution  known  to  be  normal,  and  then  be  properly  diluted  so  that  the 
two  are  equivalent,  volume  for  volume,  the  first  solution  will  also  be  normal, 
and  from  the  definition  of  normal  solutions  the  quantity  of  reagent  in  a  liter 
of  the  solution  becomes  at  once  known.  For  example,  if  a  solution  of  sul- 
phuric acid  be  made  equivalent  to  a  normal  solution  of  caustic  alkali  it  will 
then  contain  48.675  grammes  of  absolute  sulphuric  acid  per  liter.  It  is  thus 
an  easy  matter  to  prepare  normal  solutions,  although  it  may  be  impossible  to 
weigh  exactly  the  amount  of  reagent  necessary  for  a  liter  of  such  solutions. 
All  that  is  required  is  one  normal  solution  as  a  starting-point. 

Sodium  carbonate,  Na2C03,  may  be  used  as  an  alkali,  just  as  KOH  or  NaOH, 
because  it  neutralizes  acids  in  precisely  the  same  manner,  for  the  carbonic  acid 
has  no  effect,  being  volatile  and  escaping  into  the  air.  The  decomposition 
taking  place  thus: 

Na2CO3  +  2HC1  =  2NaCl  +  H2O  +  CO2,     • 

shows  that  one  molecule  of  sodium  carbonate  neutralizes  two  molecules  of 
hydrochloric  acid,  consequently  one-half  gram-molecule  of  sodium  carbonate 
must  be  taken  to  make  a  liter  of  normal  solution.  A  similar  consideration 
will  show  that  of  sodium  bicarbonate  the  whole  gram-molecule  should  be 


METHODS  FOR   QUANTITATIVE  DETERMINATIONS.        409 

taken  for  a  liter  of  normal  solution,  because  this  salt  contains  but  one  atom  of 
aodium  in  the  molecule. 

A  normal  salt  solution  may  be  defined  as  one  containing  in  a  liter  the  quan- 
tity of  salt  resulting  from  the  neutralization,  or  replacement  of  the  hydrogen 

in  a  normal  acid  solution  by  metal.     Thus,  ^^^  Na(j^  AgNO3,  BaC12?  ex- 

L  2 

pressed  in  grammes,  would  be  contained  in  a  liter  of  normal  solution  of  the 
respective  salts. 

Often  normal  solutions  are  too  strong,  and  are  diluted  ten  or  a  hundred 
times.  They  are  then  called  deci-  or  centi-normal  solutions,  respectively. 

Normal  solutions  are  generally  designated  by  *,  deci-normal  solu- 
tions by  ~y  centi-riorraal  solutions  by  ^  ;  solutions  containing  twice 
the  amount  are  designated  as  double  normal,  | ;  half  the  amount 
semi-normal,  *. 

Different  methods  of  volumetric  determination.  Of  these  we 
have  at  least  three,  which  may  be  called  the  direct,  the  indirect,  and 
the  method  of  rest  or  residue. 

The  direct  methods  are  used  in  all  cases  in  which  the  quantities  of 
volumetric  solutions  can  be  added  until  the  reaction  is  complete :  for 
instance,  until  an  alkaline  substance  has  been  neutralized  by  an  acid, 
or  a  ferrous  salt  has  been  converted  into  a  ferric  salt  by  potassium 
permanganate,  etc. 

In  the  indirect  methods  one  substance,  which  cannot  well  be  deter- 
mined volumetrically,  is  made  to  act  upon  a  second  substance,  with 
the  result  that,  by  this  action,  an  equivalent  quantity  of  a  substance 
Is  generated  or  liberated,  which  may  be  titrated.  For  instance :  Per- 
oxides, chromic  and  chloric  acids  when  boiled  with  strong  hydro- 
chloric acid,  liberate  chlorine,  which  is  not  determined  directly,  but 
is  caused  to  act  upon  potassium  iodide,  from  which  it  liberates  the 
iodine,  which  may  be  titrated  with  sodium  thiosulphate. 

The  methods  of  residue  are  based  upon  the  fact  that  while  it  is  im- 
possible or  extremely  difficult  to  obtain  complete  decomposition 
between  certain  substances  and  reagents,  when  equivalent  quantities 
are  added  to  one  another,  such  a  complete  decomposition  is  accom- 
plished by  adding  an  excess  of  the  reagent,  which  excess  is  afterward 
determined  by  a  second  volumetric  solution.  For  instance:  Car- 
bonate of  calcium,  magnesium,  zinc,  etc.,  cannot  well  be  determined 
directly,  for  which  reason  an  excess  of  normal  acid  is  used  for  their 
decomposition,  this  excess  being  titrated  afterward  by  means  of  an 
alkali. 

Indicators.  In  all  cases  of  volumetric  determination  it  is  of  the 
greatest  importance  to  observe  accurately  the  completion  of  the  reac- 


41()  ANALYTICAL  CHEMISTRY. 

tion.  In  some  cases  the  final  point  is  indicated  by  a  change  in  color, 
as,  for  instance,  in  the  case  of  potassium  permanganate,  which  changes 
from  a  red  to  a  colorless  solution,  or  chromic  acid,  which  changes 
from  orange  to  green  under  the  influence  of  deoxidizing  agents.  In 
other  cases  the  determination  is  indicated  by  the  formation  or  cessa- 
tion of  a  precipitate,  and  in  yet  others  the  final  point  could  not  be 
noticed  with  precision  unless  rendered  visible  by  a  third  substance 
added  for  that  purpose. 

Such  substances  are  termed  indicators.  Litmus,  phenolphthalein, 
methyl-orange,  etc.,  are  used  as  indicators  in  acidimetry  and  alka- 
limetry. Starch  paste  is  an  indicator  for  iodine,  potassium  chromate 
for  silver,  etc.  Of  indicators,  a  few  drops  are  in  most  cases  sufficient 
for  the  purpose.  (See  colored  Plate  VII.) 

Litmus  solution.  This  is  made  by  exhausting  coarsely  powdered  litmus  with 
boiling  alcohol,  which  removes  a  red  coloring  matter,  erythrolitmin.  The 
residue  is  treated  with  about  an  equal  weight  of  cold  water,  so  as  to  dissolve 
the  excess  of  alkali  present  in  litmus.  The  remaining  mass  is  extracted  with 
about  five  times  its  weight  of  boiling  water,  and  filtered.  The  solution  should 
be  kept  in  wide-mouthed  bottles,  stoppered  with  loose  plugs  of  cotton  to  ex- 
clude dust  but  to  admit  air.  Blue  and  red  litmus  paper  is  made  by  impregnat- 
ing strips  of  unsized  white  paper  with  the  blue  solution  obtained  by  the  above 
process,  or  with  this  solution  after  just  enough  hydrochloric  acid  has  been 
added  to  impart  to  it  a  distinct  red  tint. 

Phenolphthalein  solution.  1  gramme  of  phenolphthalein  is  dissolved  in  50  c.c. 
of  alcohol  and  water  added  to  make  100  c.c.  The  colorless  solution  is  colored 
deep  purplish-red  by  alkali  hydrates  or  carbonates,  but  not  by  bicarbonates ; 
acids  render  the  red  solution  colorless.  The  solution  is  not  suitable  as  an  indi- 
cator for  ammonia.  Carbonates  must  be  titrated  in  boiling  solution  to  drive 
off  carbon  dioxide. 

Methyl-orange  solution.  1  gramme  of  methyl-orange  (also  known  as  helian- 
thin,  tropseolin  D,  or  Poirier's  orange  3  P),  the  sodium  or  ammonium  salt  of 
dimethylamido-azobenzol-sulphonic  acid  (CH3)2N.C6H4.N.NC6H4.SO3H,  is  dis- 
solved in  1000  c.c.  of  water.  To  the  solution  is  carefully  added,  with  constant 
stirring,  jj  sulphuric  acid,  in  drops,  until  the  liquid  turns  red  and  just  ceases 
to  be  transparent;  it  is  then  filtered.  The  solution  is  yellow  when  in  contact 
with  alkaline  hydrates,  carbonates,  or  .bicarbonates.  Carbonic  acid  does  not 
affect  it,  but  mineral  acids  change  its  color  to  crimson.  It  should  be  used  in 
cold  solutions. 

Hcematoxylin  solution.  0.2  gramme  of  hsematoxylin  ((a  vegetable  coloring- 
matter  derived  from  hsematoxylon)  is  dissolved  in  100  c.c.  of  alcohol.  The  alka- 
line solution  has  a  purple  color  which  is  changed  to  yellow  or  orange  by  acids. 

Rosolic  acid  solution.  1  gramme  of  commercial  rosolic  acid  (chiefly  C20H]6O3) 
is  dissolved  in  10  c.c.  of  alcohol,  and  water  added  to  make  100  c.c.  The  solu- 
tion turns  violet  red  with  alkalies,  yellow  with  acids. 


METHODS  FOR   QUANTITATIVE  DETERMINATIONS.        411 

Other  indicators  used  at  times  in  acidimetry  are  solutions  of  bra- 
zil-wood, cochineal,  methyl-violet,  alizarin,  iodeosin,  Congo  red,  turmeric, 
etc. 

Ionic  explanation  of  the  action  of  indicators.  The  substances  used  to  indicate 
the  neutralization  point  are  themselves  very  weak  acids  or  bases,  capable  of 
forming  salts  with  the  bases  or  acids  that  are  brought  together  in  solution  for 
the  purpose  of  neutralization.  The  undissociated  molecules  of  the  indicator 
have  a  different  color  from  its  ions,  and  it  must  have  feeble  dissociating  power 
in  the  uncombined  state.  The  latter  is  a  characteristic  of  feeble  acids  in  gen- 
eral. The  salts  of  the  indicators  are  easily  dissociated  into  ions.  Substances 
that  are  strong  acids  or  bases  cannot  be  used  as  indicators,  because  they  disso- 
ciate in  the  free  state,  and  thus  give  no  different  color  when  they  are  neutral- 
ized. The  indicators  that  dissociate  least  in  the  free  state  are  the  most  sensitive 
in  color  changes  when  combined  with  traces  of  acids  or  bases.  The  neutral 
point  in  neutralization  experiments  is  really  overstepped  by  the  amount 
of  acid  or  alkali  required  to  produce  change  of  color  with  the  indicator, 
but  in  the  case  of  sensitive  indicators  this  amount  is  a  mere  trace  and  is 
negligible. 

Litmus  is  an  acid  with  slight  dissociating  power,  which  in  pure  water  gives 
a  violet  color.  Addition  of  acids  represses  the  slight  dissociation  and  the  color 
changes  to  red,  which  is  the  color  of  the  undissociated  molecules  of  litmus. 
Alkalies  form  salts  with  litmus,  which  dissociate  easily,  the  negative  ions  show- 
ing a  blue  color. 

Phenolphthalein  is  an  acid  of  less  dissociating  power  than  litmus.  In 
pure  water  or  acids  it  is  colorless,  in  alkaline  solutions  it  is  red,  which  is 
the  color  of  the  negative  ions  of  the  dissociated  molecules  of  the  salt  of  the 
indicator. 

Methyl-orange  is  an  acid  of  greater  dissociating  power  than  litmus.  It  dis- 
sociates slightly  when  greatly  diluted  in  water,  giving  a  yellow  color,  which  is 
the  color  of  the  negative  ions.  With  less  water  the  color  is  orange,  which  is 
the  resultant  of  the  yellow  color  of  the  ions  and  the  red  color  of  the  un- 
dissociated molecules.  In  acid  solutions  the  dissociation  of  the  indi- 
cator is  repressed,  and  the  color  is  pure  red.  In  alkaline  solutions,  salts 
of  the  indicator  are  formed  which  dissociate  freely  and  give  an  intense 
yellow  color. 

Because  different  indicators,  as  well  as  different  acids  and  bases,  show  great 
differences  in  their  degrees  of  dissociation,  marked  variations  in  the  sensitive- 
ness of  indicators  to  acids  and  bases  are  observed.  Hence,  indicators  must  be 
chosen  to  suit  the  particular  case  of  neutralization  in  hand  for  accurate  work. 
For  example,  if  an  active  acid  is  titrated  with  ammonia  and  phenolphthalein 
as  indicator,  color  is  not  produced  sharply  at  the  neutral  point,  because  am- 
monium hydroxide  is  so  little  dissociated  that  it  requires  an  appreciable  excess 
beyond  the  neutral  point  to  produce  the  dissociated  salt  with  the  indicator.  In 
this  case  litmus  or  methyl-orange  is  suitable  to  use. 

Titration.  This  term  is  used  for  the  process  of  adding  the 
volumetric  solution  from  the  burette  to  the  solution  of  the 


412  ANALYTICAL  CHEMISTRY. 

weighed  substance  until  the  reaction  is  completed.  We  also 
speak  of  the  standard  or  titer  of  a  volumetric  test-solution,  when 
we  refer  to  its  strength  per  volume  (per  liter  or  per  cubic  centi- 
meter). 

Of  the  principal  processes  of  titration,  or  of  volumetric  meth- 
ods used,  may  be  mentioned  those  based  upon  neutralization  (acid- 
imetrv  and  alkalimetry),  oxidation  and  reduction  (permanganates 
and  chromates  as  oxidizing,  oxalic  acid  and  ferrous  salts  as 
reducing  agents)  precipitation  (silver  nitrate  by  sodium  chloride), 
and  finally  those  which  depend  on  the  action  of  iodine  and  thio- 
sulphate  (iodimetry). 

The  substance  to  be  titrated  should  be  diluted  with  pure  water  to  a 
volume  of  about  75  c.c.  The  relationship  between  any  two  volumetric 
solutions,  for  example,  acid  and  alkali,  should  also  be  determined  in 
the  same  volume.  Any  convenient  quantity,  as  10  or  20  c.c.,  of  one 
solution  is  drawn  from  a  burette  into  a  beaker  and  diluted  to  about 
75  c.c.  before  titrating  with  the  other  solution.  If  the  comparison  is 
made  in  a  much  smaller  or  much  greater  volume,  a  somewhat  different 
relationship  will  be  found.  In  general,  the  titer  of  a  volumetric  solu- 
tion should  be  determined  in  a  volume  corresponding  approximately  to 
that  in  which  the  titration  of  a  substance  is  to  be  carried  out.  This 
is  usually  the  volume  stated  above,  but  sometimes,  for  certain  reasons, 
it  may  be  much  greater. 

Acidimetry  and  alkalimetry.  Preparing  the  volumetric  test- 
solutions  is  often  more  difficult  than  to  make  a  volumetric  deter- 
mination. Whenever  the  reagents  employed  can  be  obtained  in  a 
chemically  pure  condition  it  is  an  easy  task  to  prepare  the  solution, 
because  a  definite  weight  of  the  reagent  is  dissolved  in  a  definite 
volume  of  water.  In  many  instances,  however,  the  reagent  cannot 
be  obtained  absolutely  pure,  and  in  such  cases  a  solution  is  made  and 
its  standard  adjusted  afterward  by  methods  which  will  be  spoken  of 
later. 

Neither  the  common  mineral  acids,  such  as  sulphuric,  hydro- 
chloric, and  nitric  acids,  nor  the  alkaline  substances,  such  as  sodium 
hydroxide  or  ammonium  hydroxide,  are  sufficiently  pure  to  permit  of 
being  used  directly  for  volumetric  solutions,  because  these  substances 
contain  water,  and  an  absolutely  correct  determination  of  the  amount 
of  this  water  is  an  operation  which  involves  a  knowledge  of  gravi- 
metric methods. 


METHODS  FOR   QUANTITATIVE  DETERMINATIONS.        413 

It  is  for  this  reason  that  the  basis  in  preparing  a  volumetric  normal 
acid  solution  is  oxalic  acid,  a  substance  which  can  be  readily  obtained 
in  a  pure  crystallized  condition. 

Normal  acid  solution.  Crystallized  oxalic  acid  has  the  com- 
position H2C2O4.2H2O  and  a  molecular  weight  of  125.1.  Being 
dibasic,  only  half  of  its  weight  is  taken  for  the  normal  solution, 
which  is  made  by  placing  62.55  grammes  of  pure  crystallized  oxalic 
acid  in  a  liter  flask,  dissolving  it  in  pure  water,  filling  up  to  the 
mark  at  the  temperature  of  25°  C.  (77°  F.)  and  mixing  thoroughly. 

Normal  solutions  of  sulphuric  or  hydrochloric  acid  are,  for  various 
reasons,  often  preferred  to  oxalic  acid.  These  solutions  are  best 
made  by  diluting  approximately  the  acids  named,  titrating  the  solu- 
tion with  normal  sodium  hydroxide,  using  phenolphthalein  as  an 
indicator,  and  adding  water  until  equal  volumes  saturate  one  another. 
For  instance,  if  it  should  be  found  that  10  c.c.  normal  alkali  solution 
neutralize  7.6  c.c.  of  the  acid,  then  24  c.c.  of  water  have  to  be  added 
to  every  76  c.c.  of  the  acid  in  order  to  obtain  a  normal  solution. 
Normal  sulphuric  acid  contains  48.675  grammes  of  H2SO4,  and  normal 
hydrochloric  acid  36.18  grammes  of  HC1  per  liter. 

These  normal  solutions  can  be  made  conveniently  by  diluting  either  30  c.c. 
of  pure,  concentrated  sulphuric  acid  of  sp.  gr.  1.84,  or  130  c.c.  of  hydrochloric 
acid  of  sp.  gr.  1.16  to  1000  c.c.  The  solutions  thus  obtained  are  yet  too  con- 
centrated and  are  adjusted  as  described  above. 

Other  methods  of  determining  the  exact  standard  of  normal  acids  depend 
upon  the  precipitation  of  10  c.c.  of  the  sulphuric  acid  solution  by  barium 
chloride,  or  of  10  c.c.  of  the  hydrochloric  acid  solution  by  silver  nitrate,  and 
weighing  the  precipitated  barium  sulphate  or  silver  chloride.  Ten  c.c.  of 
normal  sulphuric  acid  give  1.1587  grammes  of  barium  sulphate,  and  10  c.c.  of 
normal  hydrochloric  acid  1.423  grammes  of  silver  chloride. 

A  third  method  depends  on  the  formation  of,  and  the  weighing  as,  an 
ammonium  salt.  Ten  c.c.  of  either  acid  are  neutralized  (or  slightly  super- 
saturated) with  ammonia  water.  The  solution  is  evaporated  in  a  previously 
weighed  platinum  dish  over  a  water-bath,  the  dry  salt  is  repeatedly  moistened 
with  alcohol,  and  finally  dried  in  an  air-bath  at  a  temperature  of  105°  C. 
(221°  F.)  for  about  half  an  hour.  Ten  c.c.  of  normal  sulphuric  acid  give  of 
ammonium  sulphate  0.65605  gramme,  and  10  c.c.  of  normal  hydrochloric  acid 
of  ammonium  chloride  0.5311  gramme. 

Normal  alkali  solution.  A  normal  solution  of  sodium  carbonate 
may  be  made  by  dissolving  52.655  grammes  (one-half  the  molecular 
weight)  of  pure  sodium  carbonate  (obtainable  by  heating  pure  sodium 
bicarbonate  to  a  low  red-heat)  in  water,  and  diluting  to  one  liter. 
This  solution,  however,  is  not  often  used,  but  may  serve  for  standard- 


414  ANALYTICAL   CHEMISTRY. 

izing  acid  solutions,  as  it  has  the  advantage  of  being  prepared  from  a 
substance  that  can  be  easily  obtained  in  a  pure  condition,  which  is 
not  the  case  in  preparing  the  otherwise  more  useful  normal  solutions 
of  potassium  or  sodium  hydroxide,  both  of  which  substances  contain 
and  absorb  water. 

The  solutions  are  made  by  dissolving  about  70  grammes  of  potas- 
sium hydroxide  or  60  grammes  of  sodium  hydroxide  in  about  1000 
c.c.  of  water,  titrating  this  solution  with  normal  acid,  and'  diluting  it 
with  water,  until  equal  volumes  of  both  solutions  neutralize  each 
other  exactly. 

The  indicators  used  in  alkalimetry  are  chiefly  solution  of  litmus 
or  phenolphthalein,  only  a  few  drops  of  either  solution  being  needed 
for  a  determination. 

The  method  adopted  by  the  U.  S.  P.  for  standardizing  the  caustic 
alkali  solution,  prepared  as  above  mentioned,  depends  on  the  use  of 
chemically  pure  potassium  bitartrate  which  acts  on  the  alkali  thus : 

KHC4H4O6  +  KOH  =  K2C4H4O6  +  H2O. 

As  the  molecular  weight  of  potassium  bitartrate  is  186.78  it  follows 
that  this  weight  in  grammes  will  neutralize  one  liter  of  normal  alkali 
solution.  The  Pharmacopoeia  directs  to  dissolve  9.339  grammes  of 
potassium  bitartrate  in  boiling  water  and  titrating  with  a  portion  of  the 
caustic  alkali  solution,  the  remainder  of  which  is  then  diluted  until  50  c.c. 
are  required  for  neutralization.  Phenolphthalein  is  used  as  indicator. 
Whenever  carbonates  are  titrated  with  acids,  or  vice  versa,  the 
solution  has  to  be  boiled  towaid  the  end  of  the  reaction  in  order  to 
drive  off  the  carbon  dioxide,  as  neither  of  the  two  indicators  men- 
tioned gives  reliable  results  in  the  presence  of  carbonic  acid  or  an 
acid  carbonate.  This  boiling  is  unnecessary  when  methyl  orange  is 
used,  because  it  is  not  influenced  by  carbonic  acid. 

When  salts  of  organic  acids  with  alkali  metals  are  to  be  titrated  with  normal 
acids,  these  salts  are  first  converted  into  carbonates.  This  is  accomplished  by 
igniting  the  weighed  quantity  of  the  salt  in  a  crucible  of  porcelain  or  platinum. 
The  chemical  action  which  takes  place  during  the  ignition  of  potassium  acetate 
may  be  shown  thus  : 

2KC2H302  -f  80  =  K2CO3  +  3H2O  +  3CO2. 

In  a  similar  manner  the  alkali  salts  of  all  organic  acids  are  converted  into 
carbonates.  Frequently  some  carbon  is  left  unburned  ;  this,  however,  does  not 
interfere  with  the  result  of  the  titration.  The  titration  is  made  with  the  liquid 
obtained  by  dissolving  in  water  the  residue  left  after  ignition. 

Method  for  calculating  results.     Before  one  can  calculate  how 
much,  say,  of  an  acid  is  in  a  solution  which  he  is  titrating  with  a 


.       METHODS  FOR    QUANTITATIVE   DETERMINATIONS.        415 

normal  alkali,  it  is  necessary  to  know  how  much  of  the  acid  in 
question  is  equivalent  to — i.  e.,  is  required  to  neutralize — one  c.c.  of 
the  alkali.  Knowing  this,  it  is  easy  to  find  how  much  acid  is  equiva- 
lent to  a  certain  number  of  c.c.  of  normal  alkali  used  in  titration. 
These  alkali  equivalents  of  normal  acid,  or  acid  equivalents  of  a 
normal  alkali,  are  easily  found  by  the  student  from  the  equation 
of  reaction. 

Thus,  to  find  how  much  HC1  is  equivalent  to  one  c.c.  of  normal  alkali,  we 
use  the  equation  : 

HC1  +  KOH  ==  KC1  +  H2O, 
36.18        55.74 
from  which  we  see  that 

36.18  gm.  HC1  =  55.74  gm.  KOH  ==  1000  c.c.  normal  KOH, 
or,  0.03618  gm.  HC1  1       "  « 

2KOH  +  H2S04  =  K2S04  +  2H2O. 
2  X  55.74      97.35 

97.35         gm.  H2SO4  =  2  X  55.74  gm.  KOH  =  2000  c.c.  normal  KOH. 
48.675         "        "  55.74    "        "      =  1000      " 

0.048675    "  1      " 

Phosphoric  acid  presents  a  peculiar  case.  When  tropaeolin  is  used  as  an 
indicator  the  change  in  color  takes  place  when  this  reaction  is  completed : 

H3P04  +  KOH  =  KH2P04  +  H20. 
97.29          55.74 
Hence, 

97.29        gm.  H3PO4  =r  55.74  gm.  KOH  ==  1000  c.c.  normal  KOH. 

0.09729     "        "       =  1      " 

With  phenolphthalein,  the  indicator  changes  color  when  the  subjoined  reac- 
tion is  completed : 

H3P04  +  2KOH  =  K2HPO4  +  2H2O. 
Hence, 

97.29        gm.  H3P04  =  2  X  55.74  gr.  KOH  ~  2000  c.c.  normal  KOH. 
or          0.04864     "        "  1      " 

The  calculation  for  the  amount  of  acid  or  alkali  is  made  in  this  way.  Sup- 
pose we  weigh  off  10  grammes  of  dilute  sulphuric  acid.  On  titrating  with 
normal  KOH  it  is  found  that  20  c.c.  are  required  to  cause  the  change  in  the 
indicator  (litmus) — i.  e.,  to  completely  neutralize  the  acid.  We  know  from  the 
above  that  1  c.c.  normal  KOH  requires  0.04867  gramme  H2SO4  for  neutraliza- 
tion, hence  20  c.c.  normal  KOH  require  0.04867  X  20  =  0.9735  gramme  H2SO4, 
That  is,  in  the  10  grammes  dilute  acid  weighed  off  there  are  0.9735  gramme 
H2SO4,  or  in  100  grammes  there  are  9.735  grammes,  or  9.73  per  cent.  This 
instance  will  serve  as  a  type  for  all  calculations  of  percentages. 

Use  of  empirical  solutions.  The  primary  advantage  in  using  normal,  deci- 
normal,  etc.,  solutions  is  the  fact  that  the  calculations  of  results  is  very  much 
simplified  in  a  system  which  involves  molecular  and  atomic  weights,  or  simple 
fractions  thereof.  But  any  solution  of  definite  strength  can  be  employed.  All 


416  ANALYTICAL   CHEMISTRY. 

normal,  decinormal,  etc.,  solutions  deteriorate  in  time,  some  very  slowly,  others 
rapidly,  especially  when  not  properly  preserved.  To  restore  the  titer  of  such 
solutions  each  time  they  are  to  be  used  involves  an  unnecessary  outlay  of  time. 
All  that  is  necessary  to  know  is  the  exact  ratio  between  the  solutions  and  a  normal 
or  decinormal  solution,  to  determine  which  an  accurately  standardized  solution 
should  be  always  available.  To  illustrate,  suppose  12.5  c.c.  of  a  hydrochloric 
acid  solution  exactly  neutralize  10  c.c.  of  normal  potassium  hydroxide  solution, 
then  1  c.c.  of  the  hydrochloric  acid  is  equivalent  to  0.8  c.c.  of  normal  acid,  and 
the  volume  of  acid  used  in  any  titration  is  readily  converted  into  the  equivalent 
volume  of  normal  acid  by  multiplying  by  the  factor  0.8. 

Neutralization  equivalents.  The  normal  solutions  of  acid  and 
alkali  may  be  used  for  the  determination  of  a  large  number  of  sub- 
stances, either  directly  (as  in  the  case  of  free  acids,  caustic  and  alka- 
line carbonates  and  bicarbonates)  or  indirectly  (as  in  the  case  of  salts 
of  most  of  the  organic  acids,  with  alkalies,  which  are  first  converted 
into  carbonates  by  ignition). 

One  c.c.  of  normal  acid  is  the  equivalent  of: 

Gramme. 

Ammonia,  NH3 0.01693 

Ammonium  carbonate,  (NHJ2CO3 0.04770 

Ammonium  carbonate  (U.  S.  P.),  NH4HCO3.NH4NH2CO2     .        .  0.05200 

Lead  acetate,  crystalHzed  Pb(C2H3O2)2.3H261         ....  0.18807 

Lead  subacetate,  Pb2O(C2H3O2)2 1 0.13593 

Lithium  benzoate,  LiC7H5O2  2 0.12711 

Lithium  carbonate,  Li2CO3 0.03675 

Lithium  citrate,  Li3C6H5O7  2 0.06952 

Lithium  salicylate,  LiC7H5O3  2 0.14299 

Potassium  acetate,  KC2H3O2  2 0.09744 

Potassium  bicarbonate,  KHCO3       .......  0.09941 

Potassium  bitartrate,  KHC4H4O6  * 0.18678 

Potassium  carbonate,  K2CO3 0.06863 

Potassium  citrate,  crystallized,  K3C6H5O7  H2O  2     .        .        .        ..  0.10736 

Potassium  hydroxide,  KOH 0.05574 

Potassium  permanganate,  KMnO4  3 0.03139 

Potassium  sodium  tartrate,  KNaC4H4O6.4H2O  2      .        .        .     '    .  0.14009 

Potassium  tartrate,  2K2C4H4O6.H2O  2 0^11679 

Sodium  acetate,  NaC2H3O2.3H2O  2 0.13510 

Sodium  benzoate,  NaC7H5O2  2         .......  0.14301 

Sodium  bicarbonate,  NaHCO3 0.08343 

Sodium  borate,  crystallized,  Na^CVlOH.O  ....'.  Q.18966 

Sodium  carbonate,  monohydrate,  Na,CO3.H2O         ....  0.06159 

Sodium  carbonate,  Na2CO3 0.05265 

Sodium  hydroxide,  NaOH       ....  0  03976 

Sodium  salicylale,  Na(C7H503)2      ..!!.'.'        .'  O.'l5889 

One  c.c.  of  normal    sodium  carbonate,  potassium   hydroxide,    or 
sodium  hydroxide,  is  the  equivalent  of: 

i  With  sulphuric  acid  and  methyl-orange.       2  After  ignition.  3  With  OXalic  acid  only. 


METHODS  FOR   QUANTITATIVE    DETERMINATIONS.        417 

Acetic  acid,  HC2H3O2  ........  0.05958 

Boric  acid,  H3IK),     ..........  0.06154 

Citric  acid,  crystallized,  H.,C6H5O7.H2O    ......  0.06950 

Hydrobromic  acid,  HBr  .........  0.08036 

Hydrochloric  acid,  HC1    .........  0.03618 

Hydriodic  acid,  HI      ..........  0.12690 

Hypophosphorous  acid,  HPH2O2      .         ......  0.06553 

Lactic  acid.  HC3H5O3       .........  0.08937 

Nitric  acid,'  HNO3       ..........  0.06257 

Oxalic  acid,  crystallized,  H2C2O4.2H2O    ......  0.06255 

Phosphoric  acid,  H3PO4  (to  form  K2HPO4;  with  phenol-phthalein)  0.04864 
Phosphoric  acid,  H3PO4  (to  form  KH2PO4  ;  with  methyl-orange)     .  0.09729 
Potassium  dichromate,  K2Cr2O7  (with  phenol-phthalein)         .         .  0.14614 
Sulphuric  acid,  H2SO4      .........  0.04867 

Tartaric  acid,  H2C4H4O6  .  .       .....        .        .         .  0.07446 

Oxidimetry.  A  normal  oxidizing  solution  is  one  which  will 
liberate  from  a  liter  as  much  oxygen  as  is  chemically  equivalent  to 
one  gram-atom  of  hydrogen.  This  is  one-half  gram-atom,  or  8 
grammes  of  oxygen,  for 

H2   +  O  =  H20,  or  H  +         = 


The  substances  generally  used  in  oxidimetry  are  potassium  per- 
manganate and  potassium  dichromate. 

Potassium  permanganate,  KMnO4,  156.98,  is  chiefly  used  for 
normal  or  decinormal  oxidizing  solution,  and  the  titration  is  always 
carried  out  in  solution  acidified  with  sulphuric  acid.  When  the  salt 
breaks  up  to  give  off  oxygen,  it  does  so  in  this  manner  : 

2KMn04  +  3H2SO4  =  K2SO4  +  2MnSO4  +  5O  +  3H2O. 

The  oxygen  is  used  in  oxidizing  the  substance  which  is  titrated. 
The  object  of  adding  the  acid  is  to  facilitate  the  decomposition  of 
the  KMnO4  and  to  take  up  the  potassium  and  manganese  to  form 
salts,  which  being  colorless  form  a  colorless  solution. 

As  2  molecules  of  permanganate  give  up  5  atoms  of  oxygen,  the 

quantity  to  be  taken  to  liberate  \  atom  or  8  gm.  is  -  ^~*  =  -f^> 

or  l  O  —  i.  e.,  J  the  molecular  weight  in  grammes,  or  31.396  gm.    It 
is  this  quantity  which  is  contained  in  one  liter  of  normal  solution. 

When  oxalic  acid  is  oxidized  with  permanganate  solution  this  reaction 
takes  place: 

H2C204.2H20  +  O  =  2C02  +  3H2O, 

or  more  fully, 

5H8C204.2H20  +  2KMn04  +  3H,SO4  =  10CO2  +  1^H2O  +  K2SO4  -f  2MnSO4. 


418  ANALYTICAL  CHEMISTRY. 

This  shows  that  one  molecule  of  oxalic  acid  requires  one  atom  of  oxygen 
for  oxidation,  or  one-half  molecule  of  acid  requires  one-half  atom  of  oxygen. 
As  one-half  gram-molecule  of  oxalic  acid  is  the  quantity  in  one  liter  of  normal 
solution,  it  follows  that  the  liter  of  normal  oxalic  acid  is  exactly  oxidized  by  a 
liter  of  normal  permanganate  solution — i.  e.,  the  two  solutions  are  equivalent, 
since  a  liter  of  normal  permanganate  solution  gives  off  one-half  gram-atom  of 
oxygen.  Hence,  it  is  convenient  to  use  normal  or  deci-normal  oxalic  acid  for 
standardizing  the  permanganate  solution. 

Permanganate  solution,  when  recently  made,  without  observing  certain  pre- 
cautions, will  deteriorate  for  a  certain  length  of  time — i.  e.,  until  all  traces  of 
organic  and  other  deoxidizing  matters  have  become  oxidized  by  the  per- 
manganate. 

To  prepare  a  permanent  ^  solution  of  potassium  permanganate,  dissolve 
about  3.3  grammes  of  the  pure  crystals  (Potassii  Permanganas,  U.  S.  P.)  in  1000 
c.c.  of  distilled  water  in  a  flask,  and  boil  for  5  minutes.  Close  the  flask  with 
absorbent  cotton,  and  set  aside  for  at  least  two  days,  so  that  suspended  matters 
may  deposit.  Then  decant  the  clear  liquid  without  stirring  up  the  sediment, 
or  for  greater  precaution  filter  it  through  a  layer  of  purified  shredded  asbestos 
(paper  or  cotton  should  not  be  used).  The  water  to  be  employed  for  di- 
luting this  solution  should  be  distilled  from  about  1  gramme  of  potassium  per- 
manganate. 

To  determine  the  strength  of  the  solution  draw  off  10  c.c.  of  deci-normal 
oxalic  acid  solution  into  a  beaker,  add  1  c.c.  of  pure  concentrated  sulphuric 
acid,  heat  the  mixture  to  about  80°  C.  (176°  F.),  then  add  gradually  from  a 
glass-cock  burette  the  permanganate,  while  stirring  constantly,  until  a  faint 
pink  color  is  produced,  which  remains  permanent  for  one-half  minute.  Note 
the  number  of  cubic  centimetres  consumed  and  dilute  the  solution  so  that  it  is 
exactly  equivalent  to  the  deci-norrnal  oxalic  acid.  Verify  the  accuracy  of  the 
dilution  by  a  new  titration.  When  properly  prepared  and  preserved  in  glass- 
stoppered  bottles,  permanganate  solution  will  keep  for  at  least  six  months  with- 
out changing  its  strength. 

A  second  method  for  preparing  a  deci-normal  solution  of  permanganate  through 
the  medium  of  a  deci-normal  thiosulphate  solution  is  described  in  the  U.  S.  P. 
as  follows : 

To  a  solution  of  about  1  gramme  of  potassium  iodide  in  10  c.c.  of  dilute  sul- 
phuric acid,  20  c.c.  of  the  permanganate  solution  to  be  standardized  are  added. 
This  reaction  takes  place  : 

2HI    +    O    =    H20    -j-     21. 

The  mixture  is  at  once  diluted  with  about  200  c.c.  of  pure  water,  and  deci-normal 
thiosulphate  solution  slowly  added  from  a  burette  with  constant  stirring  until 
the  color  of  the  iodine  is  just  discharged.  The  number  of  c.c.  of  the  thiosul- 
phate solution  is  noted,  and  the  permanganate  solution  is  diluted  so  that  equal 
volumes  of  the  two  solutions  correspond  to  each  other. 

Instead  of  using  oxalic  acid  for  standardizing  permanganate  solution, 
metallic  iron  may  be  used,  and  the  operation  should  be  conducted  as  follows : 
0.2  gramme  of  pure,  thin  iron  wire  is  dissolved  in  about  20  c.c.  of  dilute  sul- 
phuric acid  (1  acid,  5  water)  by  the  aid  of  heat,  and  in  a  flask  arranged  as 
in  Fig.  67.  The  flask  is  provided,  by  means  of  a  perforated  cork,  with  a 


METHODS  FOE    QUANTITATIVE   DETERMINATIONS.        419 

piece  of  glass  tubing,  to  which  is  attached  a  piece  of  rubber  tubing  in  which 
is  cut  a  vertical  slit  about  one  inch  long  and  which  is  closed  at  the  upper 
end  by  a  piece  of  glass  rod ;  gas  or  steam  generated  in  the  flask  may  escape, 
while  atmospheric  air  cannot  enter,  the  ferrous  solution  being  thus  protected 
from  oxidation. 

The  iron  solution,  obtained  from  the  0.2  gramme  of  iron,  is  cooled  and 
diluted  with  about  300  c.c.  of  water,  and  then  deci-normal  potassium  perman- 
ganate solution  is  added  with  constant  stirring  until  the  solution  is  tinged 
pinkish. 

As  1  c.c.  of  deci-normal  permanganate  solution   corresponds   to  0.00555 

FIG.  67. 


Flu.sk  for  dissolving  iron  for  volumetric  determination. 

gramme  of  metallic  iron,  the  0.2  gramme  of  iron  wire  used  will  consume  36.03 
c.c.  of  the  solution. 

Permanganate  is  often  used  in  determinations  of  iron  and  iron  compounds. 
Many  of  the  latter  contain  iron  in  the  ferric  state,  which  must  be  converted 
into  ferrous  compounds  before  titration.  This  conversion  is  accomplished  by 
heating  the  solution  of  a  weighed  quantity  of  the  ferric  compound  with  nascent 
hydrogen— i.  e.,  with  metallic  zinc  and  dilute  sulphuric  acid — in  a  flask 
arranged  as  the  one  spoken  of  above,  and  shown  in  Fig.  67. 

A  very  much  quicker  reduction  of  the  ferric  into  a  ferrous  compound  may  be 
accomplished  by  adding  very  slowly  with  constant  stirring  a  saturated  solution 
of  sodium  sulphite  to  the  boiling,  acidified  iron  solution  contained  in  the  flask 
until  the  liquid  becomes  colorless.  All  excess  of  sulphur  dioxide  is  expelled 
before  titrating,  by  boiling  the  solution  (which  should  contain  a  sufficient 
quantity  of  sulphuric  acid  to  decompose  all  sodium  sulphite)  for  about  ten 
minutes  in  a  flask,  arranged  as  the  one  mentioned  above. 

Equivalents.  The  equivalent  of  1  c.c.  normal  KMnO4  for  the 
various  substances  which  can  be  oxidized  by  it  must  be  deduced 
from  the  equations  of  reaction,  just  as  in  the  case  of  acids  and 
alkalies. 


420  ANALYTICAL    CHEMISTRY. 

All  nitrites  react  thus  : 

MNO2  +  O  =  MNO3,  where  M  =  metal. 
MNO2  =  1  atom  O  =  quantity  liberated  by  2  liters  —  KMnO4, 

MNQ2  =  i        «      =  l  liter  *.  KMn04, 
2  1 

MNO,  =  1  liter  ^       " 

2  X  10  10 


MNO, 


=  !  c  c       . 


2  X  10  X  1000  10 

In  this  manner  all  other  equivalents  are  found.  The  reactions 
between  permanganate  and  ferrous  salts,  and  hydrogen  dioxide  respect- 
ively, are  expressed  in  these  equations : 

2FeS04  -f  H2S04  +  O  =  Fe2(SO4)3  +  H2O. 
H202  +  O  =  H20  +  20. 

One  c.c.  of  deci-normal  potassium  permanganate,  containing  of  this 
salt  0.0031396  gramme,  is  the  equivalent  of: 

Gramme. 

Ferrous  ammonium  sulphate,  Fe(NH4)2(SO4)26H.,O     .        .        .  0.038934 

Ferrous  carbonate,  FeCO3 0.011505 

Ferrous  oxide,  FeO 0.007138 

Ferrous  sulphate,  FeSO4        ........  0.015085 

Ferrous  sulphate,  crystallized,  FeSO4.7H2O 0.027601 

Ferrous  sulphate,  dried,  2FeSO4  +  3H2O 0.017767 

Hydrogen  dioxide,  H2O2 0.001688 

Iron,  in  ferrous  compounds,  Fe -  0.005550 

Oxalic  acid,  crystallized,  H2C2O4.2H2O 0.006255 

Oxygen,  O 0.000794 

Potassium  nitrite,  KNO2        .        .        .        .        .        .        .        .  0.004227 

Sodium  nitrite,  NaNO2 0.003428 

Potassium  dichromate,  K2Cr2O7  =  292.28.  Whenever  this  salt 
oxidizes  other  substances  in  acid  solution  it  breaks  up  according  to 
this  equation : 

KaCrA  +  4H2S04  =  K2SO4  +  Cr2(SO4)3  -f  3O  +  4H2O. 

That  is,  one  molecule  of  K2Cr2O7  gives  up  three  atoms  of  oxygen. 
Hence  to  make  a  normal  solution  one-sixth  the  molecular  weight  of 
K2Cr2O7  (48.7133  grammes)  is  taken  in  the  liter,  and  one-tenth  this 
quantity,  equal  to  4.8713  grammes  of  the  pure  salt,  for  deci-normal 
solution. 

The  disadvantage  of  this  solution  is  that  the  final  point  of  titration  cannot 
be  well  seen,  for  which  reason  in  the  determination  of  iron,  for  which  it  is 


METHODS  FOR   QUANTITATIVE   DETERMINATIONS.        421 

chiefly  used,  the  end  of  the  reaction  is  determined  by  the  method  of  spotting, 
— i.  e.,  by  taking  out  a  drop  of  the  solution  and  testing  it  on  a  white  porcelain 
plate  with  a  drop  of  freshly  prepared  potassium  ferricyanide  solution  ;  when  this 
no  longer  gives  a  blue  color  the  reaction  is  at  an  end. 

In  all  determinations  by  this  solution  dilute  sulphuric  acid  has  to  be  added, 
because  both  the  potassium  and  the  chromium  require  an  acid  to  combine  with, 
as  shown  in  the  above  equation. 

The  titration  equivalents  of  this  solution  for  ferrous  salts  are  the  same  as 
those  of  deci-normal  potassium  permanganate  solution. 

lodimetry.  Solutions  of  iodine  and  of  sodium  thiosulphate  (hypo- 
sulphite) act  upon  each  other  with  the  formation  of  sodium  iodide 
and  sodium  tetrathionate : 

21  +  2Na2S2O3  =  2NaI  +  Na2S4O6. 

A  normal  solution  of  one  can  be  standardized  by  a  normal  solution 
of  the  other.  As  indicator,  is  used  starch  solution,  which  is  colored 
blue  by  minute  portions  of  free  iodine. 

Starch  solution  is  made  by  mixing  1  gramme  of  starch  with  10  c.c.  of  cold 
water,  and  then  adding  enough  boiling  water,  with  constant  stirring,  to  make 
about  200  c.c.  of  a  transparent  jelly.  If  the  solution  is  to  be  preserved  for  any 
length  of  time,  10  grammes  of  zinc  chloride  should  be  added. 

Many  other  substances,  such  as  sulphurous  acid^  hydrogen  sulphide, 
arsenous  oxide,  act  upon  iodine  with  the  formation  of  colorless  com- 
pounds, and  may,  therefore,  be  estimated  by  normal  solution  of  iodine, 
while  the  iodine  may  be  standardized  by  the  thiosulphate  solution. 
In  many  cases  the  latter  solution  is  also  used  for  the  determination  of 
chlorine,  which  is  caused  to  act  upon  potassium  iodide,  the  liberated 
iodine  being  titrated. 

Deci-normal  iodine  solution.  Iodine  being  a  univalent  element, 
the  weight  of  its  atom,  125.90,  in  grammes,  is  used  to  make  one 
liter  of  normal  solution.  Deci-normal  solution  is  generally  employed, 
and  is  made  by  dissolving  12.590  grammes  of  pure  iodine  in  a  solu- 
tion of  18  grammes  of  potassium  iodide  in  about  300  c.c  of  water, 
and  diluting  the  solution  to  1000  c.c. 

To  the  article  to  be  estimated  by  this  solution  is  added  a  little  starch 
solution,  and  then  the  iodine  solution  until,  on  stirring,  the  blue  color 
ceases  to  be  discharged. 

Iodine  of  sufficient  purity  to  permit  of  weighing  an  exact  amount  for  a  stand- 
ard solution  does  not  occur  in  the  market.  It  can  be  purified,  but  as  this  is 
somewhat  tedious,  a  simpler  plan  of  making  a  solution,  which  is  given  in  the 
U.  S.  P.,  is  generally  followed.  It  consists  in  making  a  liter  of  solution,  some- 
what stronger  than  decinormal,  by  dissolving  about  14  grammes  of  iodine 


422 


ANALYTICAL   CHEMISTRY. 


instead  of  12.59  grammes  as  described  above.  10  c.c.  of  this  solution  are  titrated, 
while  stirring  constantly,  with  deci-normalthiosulphate  solution  until  the  yellow 
color  of  iodine  just  vanishes.  The  iodine  solution  is  then  properly  diluted  so 
that  it  is  exactly  equivalent  to  the  thiosulphate  solution. 

Many  substances,  such  as  sulphurous  acid  and  its  salts,  hydrogen  sulphide, 
arsenous  oxide,  etc.,  are  acted  upon  by  iodine  in  such  a  manner  that  this 
element  enters  into  combination  with  constituents  of  the  compounds  named,  or 
iodine  acts  as  an  oxidizing  agent  through  the  medium  of  water.  The  quantity 
of  iodine  thus  taken  up  forms  the  basis  for  calculating  the  quantity  of  the  sub- 
stance acted  upon. 

In  the  case  of  arsenous  oxide  the  titration  is  made  in  alkaline  solution. 
Arsenous  oxide  and  sodium  bicarbonate  are  dissolved  in  water,  and  this  solu- 
tion, containing  sodium  met-arsenite,  is  titrated  with  iodine  solution,  when 
sodium  met-arsenate  and  sodium  iodide  are  formed : 

NaAs02  +  21  +  2NaHC03  =  NaAsO3  +  2NaI  +  H2O  +  2CO2. 

The  essential  change  in  the  above  reaction  may  be  shown  thus : 
As203  +  41  +  2H2O  =  As2O5  +  4HL 

That  is,  the  arsenous  oxide  which  may  be  considered  present  in  the  metarsenite 
is  oxidized  to  arsenic  oxide  in  the  metarsenates.  Hence  it  is  seen  that  1  liter 

As2O3 
of  one-tenth  normal  solution  is  equivalent  to  4  y  in  in  grammes. 

When  hydrogen  sulphide,  sulphurous  acid,  sulphites,  or  acid  sulphites  are  titrated 
with  iodine  the  addition  of  an  alkali  is  unnecessary ;  but  in  titrating  these  sub- 
stances they  must  be  added  to  a  measured  excess  of  iodine  solution,  and  the 
excess  after  the  reaction  is  complete  determined  by  back -titration  with  thio- 
sulphate solution ;  the  action  is  this : 

H2S  -f-      21  =  2HI       +  S. 
H2SO3  +  21  +  H2O  =  H2SO4    -f  2HI. 
Na^SOg  +  21  +  H2O  =  Na.2SO4  +  2HI. 

In  the  titration  of  antimony  and  potassium  tartrate  by  iodine  an  alkaline  solu- 
tion is  required,  and  for  this  reason  sodium  bicarbonate  is  added  to  the  solution. 
The  reaction  which  takes  place  is  somewhat  doubtful,  but  the  following  equa- 
tion, even  if  not  absolutely  correct,  corresponds  to  the  quantities  of  the  substances 
acting  upon  one  another : 

2KSbOC4H406  +  H2O  +  41  +  4NaHCO3  = 
2HSbO3  +  2KHC4H406  +  4NaI  +  4CO2  +  H2O. 

One  c.c.  of  deci-normal  iodine  solution,  containing  of  iodine 
0.01259  gramme,  is  the  equivalent  of: 

Gramme. 

Antimony  and  potassium  tartrate,  2KSbOC4H4O6.HaO          .        .  0.016495 

Arsenous  oxide,  As2O3 .  0.004911 

Hydrogen  sulphide,  H2S .  0.001691 

Potassium  sulphite,  crystallized,  K2SO3.2H2O        .                         .  0.009648 

Sodium  bisulphite,  NaHS03          ...                         .  0.005168 

Sodium  hyposulphite  (thiosulphate),  Na2S2O3.5H2O     .        .        .  0.024646 

Sodium  sulphite,  crystallized,  Na.2SO3.7H2O 0.012520 

Sulphur  dioxide,  SO2 .  0.003180 


METHODS  FOR    QUANTITATIVE  DETERMINATIONS. 
Sodium  thiosulphate  (Hyposulphite).     From  the  equation : 

2Na.2S2O3.5H2O  +        21  Na2S4O6  +  10II2O  +  2NaI. 

2X246.46  2X125.9 

we  see  that  246.46  grammes  of  crystallized  sodium  thiosulphate  are 
equivalent  to— £  e.,  will  exactly  decolorize — 125.90  grammes  of  iodine ; 
hence,  to  make  a  f  solution  of  this  compound,  246.46  grammes  must 
be  taken  in  a  liter,  and  for  a  ^  solution  24.646  grammes  are  used. 
If  the  salt  should  not  be  absolutely  pure,  a  somewhat  larger  quan- 
tity (30  grammes)  should  be  dissolved  in  1000  c.c.  of  water,  and 
this  solution  titrated  with  deci-normal  solution  of  iodine  and  diluted 
with  a  sufficient  quantity  of  water  to  obtain  the  deci-normal  solu- 
tion. 

If  a  decinormal  iodine  solution  is  not  at  hand,  and  perfectly  pure  sodium 
thiosulphate  cannot  be  obtained,  the  method  adopted  by  the  U.  S.  P.  may  be 
followed.  30  grammes  of  the  ordinary  thiosulphate  are  dissolved  and  made  up 
to  1000  c.c.  To  a  solution  of  about  1  gramme  of  potassium  iodide  in  10  c.c.  of 
dilute  sulphuric  acid  in  a  flask,  20  c.c.  of  decinormal  potassium  dichromate 
solution  are  slowly  added  from  a  burette,  and  the  solution  shaken  after  each 
addition.  The  flask  is  then  covered  with  a  watch-glass  and  allowed  to  stand  5 
minutes,  after  which  about  250  c.c.  of  pure  water  are  added,  and  the  thiosul- 
phate solution  dropped  in  from  a  burette  slowly,  with  constant  shaking,  until 
most  of  the  iodine  is  decolorized.  Finally,  a  little  starch  solution  is  added  and, 
cautiously,  more  thiosulphate  until  the  blue  color  changes  to  a  light  green. 
After  noting  the  volume  used,  the  thiosulphate  is  diluted  so  that  it  is  exactly 
equivalent  to  the  deci-normal  dichromate  solution. 

Potassium  dichromate  can  be  obtained  pure,  and  the  decinormal  solution 
easily  made  by  weighing  the  exact  quantity  needed.  The  solution,  moreover, 
is  perfectly  stable. 

The  article  to  be  tested,  containing  free  iodine,  either  in  itself  or 
after  the  addition  of  potassium  iodide,  is  treated  with  this  solution 
until  the  color  of  iodine  is  nearly  discharged,  when  a  little  starch 
liquor  is  added,  and  the  addition  of  the  solution  continued  until  the 
blue  color  has  just  disappeared. 

The  titration  of  iron  in  ferric  salts  by  thiosulphate  is  based  on 
the  liberation  of  iodine  from  potassium  iodide  by  all  ferric  salts  : 

2FeCl3     +     2KI     =     2FeCl2     +     2KC1    +     21. 

The  reaction  shown  in  the  above  equation  requires  a  temperature 
of  40°  to  50°  C.  (104°  to  122°  F.),  and  at  least  half  an  hour's  time 
to  make  sure  of  its  completion.  The  digestion  should  be  performed 


424  ANALYTICAL  CHEMISTRY. 

in  a  closed  flask.  If  iron  be  present  in  combination  with  organic 
acids,  the  addition  of  some  hydrochloric  acid  becomes  necessary. 
Before  titration  the  solution  is  allowed  to  cool,  and  the  titration 
should  be  promptly  finished,  as  otherwise  errors  by  re-oxidation  of 
the  ferrous  salt  may  be  made. 

One  c.c.  of  deci-normal  solution  of  sodium  thiosulphate,  containing 
of  the  crystallized  salt  0.024646  gramme,  is  the  equivalent  of : 

Gramme.    , 

Bromine,  Br 0.007936 

Chlorine,  Cl 0.003518 

Chromium  trioxide,  CrO3 0.003311 

Iodine,  I 0.012590 

Iron,  Fe,  in  ferric  salts 0.005550 

Deci-normal  bromine  solution  (Koppeschaar's  solution).  The 
great  volatility  of  bromine,  even  from  aqueous  solutions,  interferes 
very  much  with  the  stability  of  volumetric  solutions.  For  this 
reason  a  solution  is  prepared  which  does  not  contain  free  bromine, 
but  an  alkali  bromide  and  bromate,  from  which,  by  addition  of  an 
acid,  a  definite  quantity  of  bromine  (7.936  grammes  per  liter)  may 
be  liberated  when  required.  The  chemical  change  is  this : 
SNaBr  -f  NaBrO3  -f  6HC1  =  6NaCl  -f  3H2O  -f  6Br. 

As  the  bromine  salts  are  rarely  chemically  pure,  a  solution  is  made 
which  is  stronger  than  necessary  and  is  then  adjusted  to  the  titer  of 
thiosulphate  solution. 

The  solution  is  prepared  as  follows :  Dissolve  3.2  grammes  of  potassium 
bromate  and  50  grammes  of  potassium  bromide  in  900  c.c.  of  water.  Of  this 
solution,  which  is  too  concentrated,  transfer  20  c.c.  into  a  bottle  of  about  250  c.c., 
provided  with  a  glass  stopper.  Next  add  75  c.c.  of  water  and  5  c.c.  of  pure 
hydrochloric  acid,  and  immediately  insert  the  stopper.  Shake  the  bottle  a  few 
times  to  cause  liberation  of  the  bromine,  then  quickly  introduce  1  gramme  of 
potassium  iodide,  taking  care  that  no  bromine  vapor  escapes.  Gradually  an 
equivalent  quantity  of  iodine  is  liberated  from  the  potassium  iodide  by  the 
bromine.  When  this  has  taken  place  add,  from  a  burette,  deci-normal  thiosul- 
phate solution  until  the  iodine  tint  is  discharged,  using  toward  the  end  a  few 
drops  of  starch  solution  as  indicator!  Note  the  number  of  c.c.  of  sodium  thio- 
sulphate solution  thus  consumed,  and  then  dilute  the  bromine  solution  so  that 
equal  volumes  of  it  and  of  g  sodium  thiosulphate  solution  will  exactly  corre- 
spond to  each  other^ 

The  use  of  bromine  solution  is  directed  by  the  U.S.  P.  in  one  case  only,  viz., 
for  the  volumetric  determination  of  phenol  (carbolic  acid).     This  substance 
forms  with  bromine  tribromphenol  and  hydrobromic  acid : 
C6H5OH  +  6Br  =  C6H2Br3OH  4-  SHBr. 


METHODS  FOR    QUANTITATIVE   DETERMINATIONS.       425 

The  molecular  weight  of  phenol  is  93.36,  and  as  ii  reacts  with  6  atoms  of 
bromine,  one-sixth  of  93.36,  or  15.56  grammes  of  phenol  correspond  to  1  liter 
of  normal,  and  1.556  grammes  to  deci-normal  bromine  solution — i.  e.,  I  c.c.  of 
deci-normal  bromine  solution  corresponds  to  0.001556  gramme  of  phenol.  The 
U.  S.  P.  directs  the  assay  to  be  made  as  follows  :  Dissolve  1.556  grammes  of  the 
specimen  in  water  to  make  1  liter.  Transfer  25  c.c.  of  this  solution  (0.0389 
phenol)  to  a  glass-stoppered  bottle  of  about  200  c.c.  capacity,  and  add  30  c.c.  of 
deci-normal  bromine  solution  and  5  c.c.  of  hydrochloric  acid.  Shake  the  con- 
tents of  the  bottle  repeatedly,  during  half  an  hour,  then  quickly  introduce  1 
gramme  of  potassium  iodide,  allow  the  reaction  to  take  place  and  titrate  the 
solution  with  deci-normal  thiosulphate,  as  described  above.  Deduct  the  num- 
ber of  c.c.  of  thiosulphate  used  from  the  30  c.c.  of  bromine  solution.  The 
remainder  multiplied  by  4  indicates  the  percentage  of  phenol  in  the  carbolic 
acid  examined. 

Deci-normal  solution  of  silver.  The  pure,  dry  crystallized 
silver  nitrate,  AgNO3  =  168.69,  is  used  for  this  solution,  which  is 
made  by  dissolving  16.869  grammes  of  the  salt  in  water  to  make 
1000  c.c.  The  standard  of  this  solution  may  be  found  by  means  of 
a  deci-uormal  solution  of  sodium  chloride  containing  of  this  salt 
5.806  grammes  in  one  liter. 

Volumetric  silver  solution  is  used  directly  for  the  estimation  of 
most  chlorides,  iodides,  bromides,  and  cyanides,  including  the  free 
acids  of  these  salts.  Insoluble  chlorides  must  first  be  converted  into 
a  soluble  form  by  fusing  them  with  sodium  hydroxide,  dissolving  the 
fused  mass  (containing  sodium  chloride)  in  water,  filtering  and  neu- 
tralizing with  nitric  acid. 

The  hydroxides  and  carbonates  of  alkali  metals  and  of  alkaline 
earths  may  be  converted  into  chlorides  by  evaporation  to  dryness 
with  pure  hydrochloric  acid,  and  heating  to  about  120°  C.  (248°  F.). 
The  chlorides  thus  obtained  may  be  titrated  with  silver  solution. 

In  the  case  of  chlorides,  iodides,  and  bromides,  normal  potassium 
chromate  is  used  as  an  indicator.  This  salt  forms  wi*th  silver  nitrate 
a  red  precipitate  of  silver  chromate,  but  not  before  the  silver  chloride 
(bromide  or  iodide)  has  been  precipitated  entirely.  In  case  free  acids 
are  determined  by  silver,  these  are  neutralized  with  sodium  hydroxide 
before  titration. 

The  operation  is  conducted  as  follows :  The  weighed  quantity  of 
the  chloride  is  dissolved  in  50-100  c.c.  of  water,  neutralized  if  neces- 
sary, mixed  with  a  little  potassium  chromate,  and  silver  solution 
added  from  the  burette  until  a  red  coloration  is  just  produced,  which 
does  not  disappear  on  shaking. 

In  estimating  cyanides,  the  operation  can  be  conducted  as  above 
described,  or  it  can  be  modified,  use  being  made  of  the  formation  of 


4-26  ANALYTICAL  CHEMISTRY. 

• 

soluble  double  cyanides  of  silver  and  an  alkali  metal.      The  reaction 
takes  place  thus  : 

2KCN    +    AgN03    =    AgK(CN),    +    KNO3. 

In  the  process  adopted  by  the  U.  S.  P.,  a  suitable  quantity  of  hydrocyanic 
acid,  or  of  a  cyanide,  is  diluted  with  water,  and  5  c.c.  of  ammonia  water  and 
a  few  drops  of  potassium  iodide  solution  are  added.  Silver  solution  is  then 
added  until  a  slight  permanent  cloudiness  is  produced,  at  which  point  half  of 
the  cyanide  is  converted  into  silver  cyanide,  which  is  held  in  solution  by  the 
other  half  of  the  cyanide  as  a  double  salt.  The  least  excess  of  silver  solution 
after  this  stage  is  indicated  by  the  insoluble  silver  iodide  formed.  As  but  one- 
half  of  the  silver  solution  has  been  added  which  is  needed  for  the  complete 
conversion  of  the  cyanogen  present  into  silver  cyanide,  the  number  of  c.c.  of 
the  standard  silver  solution  employed  will  indicate  exactly  one-half  of  the 
equivalent  amount  of  cyanide  present  in  the  solution. 

One  c.c.  of  deci-normal  silver  nitrate  solution,  containing  0.016869 
gramme  of  AgNO3,  is  the  equivalent  of: 

Gramme. 

Ammonium  bromide,  NH4Br       .  0.009729 

Ammonium  chloride,  NH4C1        . 0.005311 

Ammonium  iodide,  NH4I     .  .  0.014383 

Calcium  bromide,  CaBr2       ..,.,.  .  0.009926 

Ferrous  bromide,  FeBr2 0.010711 

Ferrous  iodide,  FeI2 0.015365 

Hydriodic  acid,  HI 0.012690 

Hydrobromic  acid,  HBr       . 0.008036 

Hydrochloric  acid,  HC1       .         .        .         .         .         .         .         .  0.003618 

Hydrocyanic  acid,  HCN,  to  first  formation  of  precipitate     .         .  0.005368 

Hydrocyanic  acid,  HCN,  with  indicator 0.002684 

Lithium  bromide,  LiBr 0.008634 

Potassium  bromide,  KBr      ........  0.011822 

Potassium  chloride,  KC1 0.007404 

Potassium  cyanide,  KCN,  to  first  formation  of  precipitate   .         .  0.012940 

Potassium  cyanide,  ECN,  with  indicator 0.006470 

Potassium  iodide,  KI 0.016476 

Potassium  sulphocyanate,  KCNS 0.009653 

Sodium  bromide,  NaBr 0.010224 

Sodium  chloride,  NaCl 0.005806 

Sodium  iodide,  Nal .  0.014878 

Strontium  bromide,  SrBr2.6H2O .  0.017647 

Strontium  iodide,  SrI2.6H2O 0.022301 

Zinc  bromide,  ZnBr2 0.011181 

Zinc  chloride,  ZnCl2 0.006763 

Zinc  iodide,  ZnI2 0.015835 

Deci-normal  solution  of  sodium  chloride  is  made  by  dissolving 
5.806  grammes  of  pure  sodium  chloride  in  enough  water  to  make 
1000  c.c.  The  titration  is  made  in  neutral  solution,  normal  potas^ 
sium  chromate  being  used  as  an  indicator.  (See  explanation  in 
previous  paragraph  on  silver  solution.) 


METHODS  FOR    QUANTITATIVE   DETERMINATIONS.       427 

One  c.c.  of  deci-normal  sodium  chloride  solution,  containing 
0.005806  gramme  of  Nad,  is  the  equivalent  of: 

Gramme 

Silver,  Ag 0.010712 

Silver  nitrate,  AgNO3 0.016869 

Silver  oxide,  Ag2O 0.011506 

Deci-normal  solution  of  potassium  sulphocyanate  ( Volhard's 
solution).  This  solution,  like  the  sodium  chloride  solution,  is  used 
as  a  companion  to  silver  nitrate ;  it  has  the  advantage  that  it  can  be 
used  in  acid  solutions,  with  ferric  ammonium  sulphate  (ferric  alum) 
as  indicator.  Silver  nitrate  forms  in  the  potassium  sulphocyanate  a 
white  precipitate  of  silver  sulphocyanate  : 

KCNS  +  AgNO3  =  AgCNS  +  KNO3. 

As  indicator  is  used  ferric  alum,  which  produces  with  sulpho- 
cyanate a  deep  brownish-red  color,  which,  however,  does  not  appear 
permanently  until  all  silver  has  been  precipitated. 

As  potassium  sulphocyanate  is  rarely  pure,  10  grammes,  which  is 
about  3  per  cent,  more  than  the  quantity  required,  are  dissolved  in 
1000  c.c.  of  water.  This  solution  has  to  be  adjusted  by  standardizing 
with  deci-normal  silver  solution  until  equal  volumes  decompose  one 
another  exactly. 

The  sulphocyanate  solution  is  used  in  the  determination  of  the 
amount  of  ferrous  iodide  in  the  saccharated  salt  and  in  the  syrup. 

The  operation  is  performed  thus  :  To  the  solution  of  the  ferrous 
iodide  are  added  nitric  acid,  ferric  alum,  and  of  deci-normal  silver 
nitrate  solution  a  quantity  more  than  sufficient  to  convert  all  iodine 
into  silver  iodide.  .  The  excess  of  silver  nitrate  present  in  the  mix- 
ture is  determined  by  sulphocyanate  solution.  The  ferric  alum  and 
nitric  acid  must  not  be  added  until  the  silver  nitrate  has  precipitated 
all  iodine,  otherwise  iodine  will  be  liberated.  This  holds  in  all  cases 
where  iodides  are  titrated. 

Gas-analysis.  The  analysis  of  gases  is  generally  accomplished  by  measur- 
ing gas  volumes  in  graduated  glass  tubes  (eudiometers)  over  mercury  (in  some 
cases  over  water),  noting  carefully  the  pressure  and  temperature  at  which  the 
volume  is  determined. 

From  gas  mixtures,  the  various  constituents  present  may  often  be  eliminated 
by  causing  them  to  be  absorbed  one  after  another  by  suitable  agents.  For 
instance :  From  a  measured  volume  of  a  mixture  of  nitrogen,  oxygen,  and 
carbon  dioxide,  the  latter  compound  may  be  removed  by  allowing  the  gas  to 


428  ANALYTICAL  CHEMISTRY. 

remain  in  contact  for  a  few  hours  with  potassium  hydroxide,  which  will  absorb 
all  carbon  dioxide,  the  diminution  in  volume  indicating  the  quantity  of  carbon 
dioxide  originally  present.  The  volume  of  oxygen  may  next  be  determined  by 
introducing  a  piece  of  phosphorus,  which  will  gradually  absorb  the  oxygen, 
the  remaining  volume  being  pure  nitrogen. 

In  some  cases  gaseous  constituents  of  liquids  or  solids  are  eliminated  and 
measured  as  gases.  Thus,  the  carbon  dioxide  of  carbonates,  the  nitrogen 
dioxide  evolved  from  nitrates,  the  nitrogen  of  urea  and  other  nitrogenous 
bodies,  are  instances  of  substances  which  are  eliminated  from  solids  in  the 
gaseous  state  and  determined  by  direct  measurement. 

The  gas  volume  thus  found  is,  in  most  cases,  converted  into  parts  by  weight. 
The  basis  of  this  calculation  is  the  weight  of  1  c.c.  of  hydrogen,  which,  at  the 
temperature  of  0°  C.  (32°  F.)  and  a  pressure  of  760  mm.  of  mercury  is  0.0000898 
gramme.  1  c.c.  of  any  other  gas  weighs  as  many  times  the  weight  of  1  c.c. 
hydrogen  as  the  molecule  of  this  substance  is  heavier  than  that  of  hydrogen. 
Thus  the  molecular  weight  of  carbon  dioxide  is  21.835  times  greater  than  that 
of  hydrogen,  consequently  1  c.c.  of  carbon  dioxide  weighs  21. 835  times  heavier 
than  1  c.c.  of  hydrogen,  or  0.0019608  gramme. 

It  has  been  shown  on  pages  26  and  45  that  heat  and  pressure  cause  a  regular 
increase  or  decrease  in  volume.  The  data  there  given  are  used  in  calculating 
the  volume  of  the  measured  gas  at  the  temperature  of  0°  C.  (32°  F.)  and  a 
pressure  of  760  m.m. 

The  reason  for  reducing  volumes  of  gases  to  0°  C.  and  760  m.m.  pressure, 
known  as  normal  temperature  and  pressure,  is  that  the  densities  of  gases  are 
given  for  these  conditions.  Therefore,  to  find  the  weight  of  any  volume  of 
gas  it  must  be  reduced  to  normal  temperature  and  pressure. 

A  simple  rule  for  reducing  volumes  of  gases  to  0°  C.  is  this :  The  volume  of 
a  gas  is  proportional  to  its  absolute  temperature.  The  absolute  temperature  is 
obtained  by  adding  273°  to  the  reading  of  the  centigrade  scale.  Thus,  if  a  gas 
measures  66  c.c.  at  54.6°  C.,  its  volume  at  0°  C.  is  found  from  the  proportion : 

66  c.c.  :  [54.6°  +  273°]  :  :  x  :  [0°  +  273°], 
or, 

66  :    327.6  : :  x  :  273, 
and  •» 


In  this  reduction  the  pressure  is  supposed  to  remain  constant.  That  is,  the 
volume  of  55  c.c.  at  0°  C.  is  still  at  the  same  pressure  as  the  volume  66  c.c.  was. 

To  reduce  a  gas  volume  under  any  pressure  to  the  volume  it  would  occupy 
if  the  pressure  were  changed  to  the  normal — i.  e.,  to  760  m.m. — use  is  made  of 
Boyle's  law,  viz.,  the  product  of  the  pressure  times  the  corresponding  volume 
of  a  gas  is  always  constant  when  the  temperature  is  the  same.  This  law  is 
expressed  in  the  equation,  PV=pv,  where  PV  and  pv  are  corresponding 
pressures  and  volumes. 

If  we  assume  that  in  the  above  case  the  volume  of  55  c.c.  is  under  a  pressure 
of  750  m.m.,  its  volume  at  normal,  or  760  m.m.  pressure,  is  found  by  using  the 
equation : 

55  X  750  =  x  X  760, 


METHODS  FOR   QUANTITATIVE  DETERMINATIONS.       429 

This  shows  that  the  gas-volume  of  66  c.c.  at  54.6°  C.  and  750  m.m.  pressure 
becomes  54.28  c.c.  at  0°  C.  and  760  m.m.  pressure.  Knowing  the  volume  at 
0°  C.  and  760  m.m.  pressure,  and  the  weight  of  1  c.c.  of  the  gas  under  these 
conditions,  the  weight  of  the  total  volume  is  easily  found. 

The  reduction  for  temperature  and  pressure  can  be  made  in  one  operation 
by  using  the  formula : 

V  =      v  X  P  X  273 

760  X  (273  -f  t) ' 

V=  volume  at  0°  C.  and  760  m.m.  pressure,  which  is  to  be  found. 

v  =  volume  read  at  some  pressure,  p,  other  than  the  normal. 

t  =  temperature  in  centigrade  degrees  at  which  volume  v  is  read. 

Thus,  in  above  case : 

V  =       66  X  750  X  273        =  ,,  2g 

760  X  (273°  -f-  54.6) 

Methods  of  gas-analysis  have  been  adopted  by  the  U.  S.  P.  in  the  quantita- 
tive determination  of  amyl  nitrite  and  ethyl  nitrite.  The  operation  is  per- 
formed in  an  apparatus  known  as  a  nitrometer,  consisting  of  two  glass  tubes  held 
in  upright  position  and  connected  at  the  lower  ends  by  a  piece  of  rubber 
tubing.  One  of  the  tubes  is  open,  the  other  one  is  graduated  and  provided 
with  a  glass  stopcock  near  the  upper  end.  In  using  the  nitrometer  for  the 
analysis  of  ethyl  nitrite  the  graduated  tube  is  filled  with  saturated  solution  of 
sodium  chloride,  in  which  nitrogen  dioxide  is  almost  insoluble.  Next  are 
introduced  through  the  stopcock  the  measured  (or  weighed)  quantity  of  ethyl 
nitrite  with  a  sufficient  amount  of  solution  of  potassium  iodide  and  sulphuric 
acid.  By  the  action  of  these  agents  nitrogen  dioxide  is  liberated,  and  from  the 
volume  obtained  the  quantity  of  nitrite  present  is  calculated.  The  decom- 
position is  shown  by  the  equation  : 

C2H5N02  -f  KI  +  H2S04  =  C2H5OH  +  I  +  KHSO4  +  NO. 

Water  analysis.  The  objects  of  water  analysis  are  various.  Thus,  the 
analysis  may  serve  to  decide  the  fitness  of  a  water  for  manufacturing,  medici- 
nal, or  household  purposes.  Accordingly,  more  or  less  stress  is  laid  on  the 
exact  determination  of  certain  constituents.  While  the  student  is  referred  to 
special  books  treating  on  the  different  methods  of  water  analysis,  a  brief  outline 
of  the  chemical  examination  of  drinking-water  is  here  given. 

It  should  be  remembered  that  the  results  obtained  by  chemical  examination 
only  are  sometimes  insufficient  to  furnish  positive  proof  of  the  fitness  of  a 
water  for  drinking-purposes.  The  reason  is  that  micro-organisms  may  be 
present  which  cannot  be  detected  by  chemical  means.  It  is  the  microscope, 
aided  by  appropriate  bacteriological  methods,  which  has  to  be  used  in  such 
cases,  and  these  methods  cannot,  of  course,  be  considered  in  this  book. 

Standard  of  purity.  A  fixed  standard  has  not  as  yet  been  generally 
adopted  for  judging  the  purity  of  wholesome  drinking-water,  but  most  authori- 
ties agree  that  the  following  maxima  of  admixtures  should  not  be  exceeded. 
They  are  expressed  in  milligrams  per  liter — i.  e.,  parts  by  weight  in  one  million. 
The  following  data  refer  to  one  liter  of  water  used : 


430  ANALYTICAL  CHEMISTRY. 

Total  residue  left  on  evaporation  :  500  mg. 

Potassium    permanganate    decomposed    by    organic    matter:      10  mg. 

(=31.71  c.c.  ^KMn04). 

Ammonia,  present  as  such  or  as  an  ammonium  salt :  0.05  mg. 
Albuminoid  ammonia— i.  e.,  ammonia  formed  from  nitrogenous  organic 

matter  by  distillation  with  KMnO4 :  0.1  mg. 
Mtrates :  10  mg.  of  N2O5. 

Nitrites :  a  mere  trace,  not  to  exceed  Q.05  mg.  of  N2O3. 
Sulphates  :  60  to  100  mg.  of  H2S04. 
Chlorine :  15  mg. 
Phosphates :  a  mere  trace. 
The  water  should  be  clear,  colorless,  odorless  and  practically  tasteless. 

Total  solids.  If  the  water  be  turbid,  a  liter  of  it  is  passed  through  a  small 
filter,  previously  dried  and  weighed.  After  drying  at  110°  C.,  filter  and  con- 
tents are  weighed  together  and  the  difference  is  quantity  of  suspended  solids. 
The  evaporation  to  dryness  of  one  liter  of  the  clear  water  in  a  platinum  or 
nickel  dish  at  a  moderate  temperature,  with  subsequent  heating  to  110°  C., 
gives  the  total  inorganic  and  organic  solids  in  solution. 

The  subsequent  heating  of  the  dried  residue  to  redness  causes  the  expul- 
sion of  all  organic  matter ;  but  as  also  inorganic  matters,  such  as  carbon  dioxide 
from  acid  carbonate,  oxygen  from  nitrates,  etc.,  may  escape,  the  determination 
is  of  relatively  little  value. 

Organic  matters.  While  we  have  no  good  method  by  which  the  quantity 
of  organic  matter  in  water  can  be  readily  determined,  the  oxidizing  power  of 
permanganate  for  organic  matters  is  used  for  an  approximate  determination. 
This  is  made  by  acidifying  100  c.c.  of  water  with  5  c.c.  of  sulphuric  acid,  and 
adding  10  c.c.  of  -~-  potassium  permanganate,  or  enough  to  impart  a  distinct 

red  color.  The  liquid  is  boiled  for  ten  minutes.  Should  the  red  color  disap- 
pear, more  permanganate  must  be  added.  When  color  remains  permanent, 
10  c.c.  of  ~  oxalic  acid  are  added  and  the  mixture  is  again  heated.  To  this 

solution  permanganate  is  added  until  it  shows  a  red  tint.  From  the  total 
number  of  c.c.  of  permanganate  used,  10  c.c.  are  deducted  for  the  oxalic  acid 
added. 

As  the  organic  constituents  in  water  at  different  times  and  places  have  no 
uniform  composition,  the  quantity  of  organic  matter  present  cannot  be  calculated 
from  the  quantity  of  permanganate  used.  It  is  therefore  customary  to  speak 
simply  of  the  oxygen- consuming  power  of  water.  It  should,  however,  be  re- 
membered that  water  may  contain  deoxidizing  agents,  other  than  organic 
matters,  such  as  hydrogen  sulphide,  nitrites,  ferrous  salts,  etc. 

Ammonia.  Nitrogenous  organic  matters,  when  undergoing  decomposition 
by  the  agency  of  bacteria,  generate  ammonia,  which  is  gradually  converted 
into  nitrites  and  nitrates.  It  is  for  this  reason  that  the  presence  of  these  three 
compounds  is  looked  upon  as  indicative  of  nitrogenous  matters,  though  small 
quantities  of  ammonia  and  nitrites  may  also  be  present  in  the  water  by  ab? 
sorption  from  the  air. 


METHODS  FOR    QUANTITATIVE  DETERMINATIONS.       431 

It  is  customary  to  speak  in  water  analysis  of  free  ammonia  and  albuminoid 
ammonia.  By  free  ammonia  is  meant  the  ammonia  present  as  ammonium 
hydroxide,  or  more  generally  as  an  ammonium  salt,  chiefly  carbonate.  Albu- 
minoid ammonia  refers  to  the  ammonia  obtainable  from  nitrogenous  matter 
by  oxidation  with  alkaline  permanganate  solution. 

The  process  for  the  determination  of  both  kinds  of  ammonia  is  carried  out 
as  follows:  500  c.c.  of  the  water  are  placed  in  a  flask  of  about  one  liter 
capacity  and  5  c.c.  of  a  saturated  solution  of  sodium  carbonate  are  added.  The 
flask  is  connected  with  a  suitable  condenser  whose  outlet  is  so  connected  with  a 
receiver  that  no  loss  of  ammonia  can  occur.  Heat  is  then  applied  to  the  flask 
until  300  c.c.  have  distilled  over.  To  this  distillate,  containing  all  the  "  free 
ammonia,"  is  added  enough  pure  water  to  restore  the  original  volume  of  500 
c.c.,  and  the  distillate  is  s^t  aside  for  Nesslerizing. 

To  the  liquid  remaining  in  the  distilling  flask  are  now  added  50  c.c.  of  an 
alkaline  permanganate  solution  (made  by  dissolving  8  gm.  of  KMnO4  and  200 
gm.  KOH  in  water  to  make  1  liter),  and  distillation  is  resumed  until  200  c.c. 
have  passed  over,  which  distillate  is  also  diluted  to  the  original  volume  of 
water  used — i.  e.,  to  500  c.c. 

Both  distillates,  containing  the  free  and  the  albuminoid  ammonia  respect- 
ively, are  now  ready  to  be  tested  for  ammonia  by  a  method  depending  on 
the  intensity  of  color  imparted  to  them  by  Nessler's  reagent.  This  reagent 
gives  with  highly  diluted  ammonia  a  color  varying  from  pale  straw-yellow  to 
brown.  In  order  to  have  a  standard  for  comparison  of  the  colors,  an  empirical 
solution  of  ammonium  chloride  is  made,  containing  of  this  salt  3.137  gm.  in  1 
liter,  corresponding  to  1  mg.  of  NH3  in  each  c.c.  Just  before  use,  5  c.c.  of  this 
solution  are  diluted  with  pure  water  to  100  c.c.,  of  which  1  c.c.  now  contains 
0.05  mg.  NH3. 

To  make  the  test  there  are  required  five  small  cylinders  of  colorless  glass, 
of  about  30  m.m.  diameter  and  about  100  m.m  high,  each  having  a  mark  at  50 
c.c.,  and  being  numbered  from  1  to  5.  Into  four  of  these  cylinders  are  measured 
0.5,  1,  1.5,  and  2  c.c.,  respectively,  of  the  standard  ammonium  chloride  solu- 
tion, and  all  are  then  filled  with  water  up  to  the  50  c.c.  mark.  This  makes  the 
contents  of  the  four  cylinders  correspond  to  water  containing  0.5,  1,  1.5,  and  2 
mg.  of  NH3  per  liter. 

Cylinder  No.  5  is  next  filled  with  50  c.c.  of  the  water  specimen  prepared  for 
the  ammonia  determination,  and  to  each  of  the  five  cylinders,  standing  on  white 
paper,  is  added  1  c.c.  of  ^essler's  reagent  (see  index),  which  is  well  mixed  with 
the  water.  A  comparison  of  the  yellow  color  produced  in  the  sample  with  that 
of  the  cylinders  1  to  4,  containing  known  quantities,  will  afford  an  estimate  of 
the  quantity  of  ammonia  in  the  water  examined. 

Should  the  color  of  the  specimen  be  deeper  than  that  of  cylinder  No.  4,  or 
lighter  than  that  of  No.  1,  then  the  experiment  has  to  be  repeated,  the  water 
or  the  standard  solution  being  diluted  in  definite  proportions  until  similarity 
of  color  is  reached.  The  calculation  is  based  on  the  dilution  made. 

Of  course,  both  distillates  have  to  be  treated  in  this  manner.  Great  care 
must  be  taken  to  make  sure  that  the  water,  reagents,  and  apparatus  used  in 
the  operation  are  absolutely  free  from  ammonia.  When  only  free  ammonia  is 
to  be  determined  the  distillation  can  be  dispensed  with.  If  the  water  should 
contain  any  considerable  quantity  of  calcium  salts,  these  must  be  precipitated 


432  ANALYTICAL   CHEMISTRY. 

by  digesting  the  water  with  a  little  sodium  carbonate  and  sodium  hydroxide 
before  Nesslerizing. 

Nitric  acid.  While  there  are  methods  by  which  nitric  acid  can  be  deter- 
mined more  accurately,  it  often  suffices  to  make  the  tests  with  brucine, 
diphenylamine,  and  pyrogallic  acid,  as  described  under  the  analytical  reactions 
of  nitric  acid  on  page  177. 

Nitrous  acid.  A  solution  made  by  dissolving  1  gm.  of  metaphenylene- 
diamine  in  200  c.c.  water,  containing  5  gm.  H2SO4,  is  used  for  the  determina- 
tion of  nitrites  in  the  same  manner  as  Nessler's  solution  is  used  for  ammonia. 
The  required  standard  nitrite  solution  is  prepared  by  dissolving  0.406  gm.  silver 
nitrite  and  0.225  gm.  potassium  chloride  in  hot  water,  mixing  and,  after  cool- 
ing, filling  up  to  1  liter.  After  filtering  off  the  precipitated  silver  chloride, 
lOo'c.c.  of  the  nitrate  are  diluted  to  1000  c.c.  This  solution  contains  nitrous 
acid  equivalent  to  10  mg.  of  N2O3  per  liter. 

Metaphenylene-diamine  solution,  prepared  as  above,  gives  with  nitrites  a 
yellow  color,  the  intensity  of  which  serves  for  the  quantitative  estimation  of  the 
nitrites  present.  The  test  is  made  by  using  definite  dilutions  of  the  above 
standard  nitrite  solution  in  the  four  test-cylinders,  adding  1  c.c.  of  the  meta- 
phenylene-diamine  to  each  50  c.c.,  and  comparing  the  colors  produced  with  that 
obtained  in  the  water  specimen,  treated  in  like  manner.  Immersion  of  the 
cylinders  in  warm  water  accelerates  the  reaction. 

Sulphates.  While  there  are  volumetric  methods  for  the  determination  of 
sulphates,  this  can  be  conveniently  made  by  the  gravimetric  method — i.  e.t  by 
precipitating  the  sulphate  with  barium  chloride  and  weighing  the  precipitated 
BaS04.  From  100  to  250  c.c.  of  water  should  be  used. 

Chlorine.  If  the  water  under  examination  has  had  an  opportunity  to 
become  charged  with  sodium  chloride  from  its  proximity  to  the  sea  coast,  to 
salt  lakes,  or  by  flowing  through  strata  containing  salt  deposits,  then  a  con- 
siderable quantity  of  chlorides  may  be  present  and  yet  the  water  may  be  used 
without  detriment  to  health.  But  in  other  cases  the  chlorides  are  derived 
from  cesspools,  sewage,  etc.,  and  their  presence  is  then  indicative  of  dangerous 
pollution. 

The  determination  of  chlorine  is  made  by  titrating  100  c.c.  of  water  with 
^  AgN03,  using  potassium  ~,hromate  as  an  indicator.  For  water  containing 
much  organic  matter  the  gravimetric  method  should,  be  used. 

Phosphates.  The  ammonium  molybdate  test  (see  analytical  reactions  of 
phosphoric  acid,  page  228)  should  give  no  indication  of  phosphoric  acid,  as  the 
presence  of  soluble  phosphates  in  water  is  almost  positive  proof  that  pollution 
with  urine  has  taken  place. 

QUESTIONS. — Explain  the  principles  which  are  made  use  of  in  gravimetric 
and  volumetric  determinations.  Give  an  outline  of  the  operations  to  be  per- 
formed in  the  gravimetric  determination  of  copper  in  cupric  sulphate.  What 
are  normal  and  deci-normal  solutions,  and  how  are  they  made?  What  is  the 
use  of  indicators  in  volumetric  analysis  ?  Mention  some  indicators  and  explain 


DETECTION  OF  IMPURITIES.  433 

39.    DETECTION  OF  IMPURITIES  IN  OFFICIAL  INOKGANIC 
CHEMICAL  PREPARATIONS. 

General  remarks.  Very  little  has  been  said,  heretofore,  about 
impurities  which  may  be  present  in  the  various  chemical  prepara- 
tions, and  this  omission  has  been  intentional,  because  it  would  have 
increased  the  bulk  of  this  book  beyond  the  limits  considered  neces- 
sary for  the  beginner. 

Impurities  present  in  chemical  preparations  are  either  derived  from 
the  materials  used  in  their  manufacture,  or  they  have  been  intention- 
ally added  as  adulterations.  In  regard  to  the  last,  no  general  rule 
for  detecting  them  can  be  given,  the  nature  of  the  adulterating  article 
varying  with  the  nature  of  the  substance  adulterated  ;  the  general 
properties  of  the  substance  to  be  examined  for  purity  will,  in  most 
cases,  suggest  the  nature  of  those  substances  which  possibly  may  have 
been  added,  and  for  them  a  search  has  to  be  made,  or,  if  necessary,  a 
complete  analysis,  by  which  is  proved  the  absence  of  everything  else 
but  the  constituents  of  the  pure  substance. 

Impurities  derived  from  the  materials  used  in  the  manufacture  of 
a  substance  (generally  through  an  imperfect  or  incorrect  process  of 
manufacture),  or  from  the  vessels  used  in  the  manufacture,  are  usually 
but  few  in  number  (in  any  one  substance),  and  their  nature  can,  in 
most  cases,  be  anticipated  by  one  familiar  with  the  process  of  manu- 
facture. For  one  not  acquainted  with  the  mode  of  preparation  it 
would  be  a  rather  difficult  task  to  study  the  nature  of  the  impurities 
which  might  possibly  be  present. 

their  action.  Why  is  oxalic  acid  preferred  in  preparing  normal  acid  solution? 
What  quantity  of  oxalic  acid  is  contained  in  a  liter,  and  why  is  this  quantity 
used?  Suppose  2  grammes  of  crystallized  sodium  carbonate  require  14  c.c. 
of  normal  acid  for  neutralization :  What  are  the  percentages  of  crystallized 
sodium  carbonate  and  of  pure  sodium  carbonate  contained  in  the  specimens 
examined.  Ten  grammes  of  dilute  hydrochloric  acid  require  35.5  c.c.  of  nor- 
mal sodium  hydroxide  solution  for  neutralization ;  what  is  the  strength  of 
this  acid?  Explain  the  action  of  potassium  permanganate  and  of  potassium 
dichromate  when  used  for  volumetric  purposes.  Which  substances  may  be 
determined  volumetrically  by  solutions  of  iodine  and  sodium  thiosulphate? 
Explain  the  mode  in  which  the  determinations  by  these  agents  are  accom- 
plished. Suppose  1  gramme  of  potassium  iodide  requires  for  titration  60  c.c. 
of  deci-normal  solution  of  silver  nitrate:  What  quantity  of  pure  potassium 
iodide  is  indicated  by  this  determination?  Describe  in  detail  the  volumetric 
determination  of  carbolic  acid.  For  what  purposes  is  potassium  sulphocya- 
nate  used  volumetrically,  and  what  is  its  action  ?  Explain  the  method  used 
for  the  analysis  of  ethyl  nitrite. 
28 


434  ANALYTICAL  CHEMISTRY. 

The  same  remarks  apply  to  the  methods  by  which  the  impurities 
can  be  detected.  One  familiar  with  analytical  chemistry  can  easily 
find,  in  most  cases,  a  good  method  by  which  the  presence  or  absence 
of  an  impurity  can  be  demonstrated  ;  but  to  one  unacquainted  with 
chemistry  it  might  be  an  impossibility  to  detect  impurities,  even  if 
a  method  were  given. 

For  these  reasons  little  stress  has  been  laid  upon  the  occurrence  of 
impurities  in  the  various  chemical  preparations  heretofore  considered. 
Moreover,  the  U.  S.  P.  gives,  in  most  cases,  directions  for  the  detec- 
tion of  impurities,  so  explicit  that  anyone  acquainted  with  analytical 
operations  will  find  no  difficulty  in  performing  these  tests  satisfac- 
torily. 

However,  while  the  Pharmacopeia  gives  exact  instructions  how  to 
manipulate,  it  furnishes  no  explanations  why  certain  methods  have 
been  adopted,  or  why  certain  operations  are  to  be  performed.  It  is 
for  this  reason,  and  for  the  special  benefit  of  the  beginner,  that  a  few 
paragraphs  are  devoted  to  the  consideration  of  official  methods  for 
testing  the  chemical  preparations  of  the  U.  S.  P. 

Official  chemicals  and  their  purity.  Absolute  purity  of  chemi- 
cals is  essential  in  some  cases,  as,  for  instance,  when  they  are  intended 
as  reagents ;  such  chemicals  are  commercially  designated  as  C.  P. 
(chemically  pure).  For  the  majority  of  medicinal  chemicals,  how- 
ever, such  absolute  purity  is  unnecessary,  as  the  small  proportion  of 
harmless  impurities  present  in  nowise  interferes*  with  the  therapeutic 
action  of  the  substance,  and  a  demand  for  absolute  purity,  which 
greatly  enhances  the  cost  of  chemicals,  is  therefore  unreasonable  and 
not  required  by  the  Pharmacopeia. 

The  presence  of  a  small  fraction  of  one  per  cent,  of  sodium  chloride 
in  many  official  chemicals  cannot  be  looked  upon  as  objectionable, 
while  the  same  amount  of  arsenic  would  render  the  preparation  unfit 
for  medicinal  use. 

The  methods  used  by  the  Pharmacopoeia  to  determine  the  qualit/ 
of  a  chemical  preparation  may  be  divided  into  four  classes,  as  follows : 
1.  Tests  as  to  identity  ;  2.  Qualitative  tests  for  impurities ;  3.  Quan- 
titative tests  for  the  limit  of  impurities  ;  4.  Quantitative  determina- 
tion of  the  chief  constituent. 

Tests  as  to  identity.  These  tests  are  partly  of  a  physical,  partly 
of  a  chemical  character.  They  include,  in  the  physical  part,  the 
examination  of  the  appearance,  color,  crystalline  structure,  specific 
gravity,  fusing-point,  boiling-point,  etc. 


DETECTION  OF  IMPURITIES.  435 

The  chemical  tests  given  are  sufficiently  characteristic  to  leave  no 
doubt  as  to  the  true  nature  or  identity  of  the  substance.  In  order  to 
accomplish  this  object  it  is  not  necessary  to  apply  all  the  analytical 
reagents  characteristic  of  the  substance  or  its  component  parts,  but 
the  U.  S.  P.  selects  from  the  often  large  number  of  known  tests  one, 
or  possibly  a  few,  which  answer  best  in  the  special  case. 

For  instance,  while  we  have  a  number  of  tests,  both  for  potassium 
and  iodine,  the  U.  S.  P.,  in  the  article  on  potassium  iodide,  gives  but 
one  reaction  for  each  of  these  elements.  Yet  these  tests  have  been 
selected  with  sufficient  judgment  to  admit  of  no  doubt  regarding  the 
nature  of  the  substance. 

Qualitative  tests  for  impurities.  These  tests  are  in  many  cases 
described  minutely,  i.  e.,  the  quantity  to  be  taken  of  both  the  sub- 
stance to  be  examined  and  the  reagent  to  be  added  is  stated.  More- 
over the  amount  of  solvent  (water,  acid,  etc.)  to  be  used  is  mentioned, 
and  other  details  are  given.  The  object  of  this  exactness  in  describ- 
ing the  tests  is  not  only  to  render  the  work  easy  for  one  not  fully 
familiar  with  analytical  methods,  but  also,  in  some  cases,  to  fix  a 
limit  for  the  admissible  quantity  of  an  impurity.  A  certain  reagent 
may,  in  a  concentrated  solution,  indicate  the  presence  of  a  trace  of 
an  impurity,  while  in  a  more  dilute  solution  this  reagent  will  fail  to 
detect  it.  The  selection  of  the  reagents  used  in  certain  tests  is  also 
made  with  the  view  of  establishing  a  sufficient  purity  for  pharmaco- 
poeial  purposes  of  the  article  examined  without  demanding  an  absolute 
purity. 

A  few  instances  may  help  to  illustrate  these  remarks  :  Potassium 
can  be  precipitated  from  a  solution  of  its  salts  by  a  number  of  re- 
agents, which,  however,  differ  widely  in  sensitiveness.  Thus,  tartaric 
acid  will  cause  the  formation  of  a  precipitate  of  potassium  bitartrate 
in  a  solution  containing  at  least  0.1  per  cent,  of  potassium ;  in  solu- 
tions containing  a  less  amount  no  precipitate  is  formed.  Platinic 
chloride  is  somewhat  more  sensitive  than  tartaric  acid,  and  sodium 
cobaltic  nitrite,  which  is  still  more  delicate,  causes  a  precipitate  in 
solutions  containing  even  as  little  as  0.04  per  cent,  of  potassium.  It 
is  evident  that  by  using  either  one  or  the  other  of  the  three  reagents 
mentioned  for  the  detection  of  potassium,  this  metal  may  or  may  not 
be  found,  according  to  the  quantity  present  in  a  solution.  The 
Pharmacopoeia,  in  directing  the  use  of  one  of  these  reagents,  limits 
the  amount  of  a  permissible  quantity  of  potassium  according  to  the 
sensitiveness  of  the  reagent. 


ANALYTICAL   CHEMISTRY. 

Again,  in  testing  for  arsenic,  the  chemist  has  his  choice  between  a 
number  of  more  or  less  delicate  tests.  Gutzeit's  test  is  so  sensitive 
that  by  means  of  it  arsenic  can  be  detected  in  a  solution  containing 
only  0.000001  gramme  of  arsenous  oxide  in  a  cubic  centimeter.  This 
test  would  be,  therefore,  by  far  too  severe  when  applied  to  a  number 
of  pharmaceutical  preparations,  for  which  reason  the  Pharmacopoeia 
directs  in  many  cases  the  less  sensitive  hydrogen  sulphide  test. 

Quantitative  tests  for  the  limit  of  impurities.  While,  as  above 
stated,  even  the  qualitative  tests  are  often  so  made  as  to  be  to  some 
extent  of  a  quantitative  character,  the  U.  S.  P.  recommends  in  many 
cases  methods  by  which  a  stated  limit  of  an  impurity  can  be  detected 
without  the  necessity  of  determining  by  quantitative  analysis  the 
actual  amount  of  the  impurity  present. 

Formerly  it  was,  and  to  some  extent  it  is  now,  customary  to  limit 
the  amount  of  a  permissible  quantity  of  an  impurity  by  referring  to 
the  intensity  of  the  reaction.  In  case  the  impurity  was  to  be  detected 
by  precipitation  (as,  for  instance,  sulphates  or  chlorides  in  potassium 
nitrate)  it  was  stated  that  the  respective  reagents  used  for  the  detec- 
tion (in  the  case  named,  barium  chloride  or  silver  nitrate)  should  not 
produce  more  than  a  very  slight  precipitate,  or  turbidity,  or  cloudi- 
ness, etc.  These  descriptions  are,  of  course,  very  indefinite,  and  the 
conclusion  arrived  at  depends  largely  upon  the  individuality  of  the 
observer. 

In  order  to  obviate  this  uncertainty  the  U.  S.  P.  has  introduced  a 
number  of  more  exact  methods.  These  depend  upon  the  addition  of 
a  definite  quantity  of  a  reagent  capable  of  eliminating  a  certain  quan- 
tity of  the  impurity  from  a  given  quantity  of  the  substance  to  be 
examined.  In  thus  examining  a  preparation  the  impurity  may  or 
may  not  be  present ;  if  present,  the  permissible  quantity  will  be  re- 
moved by  the  operation,  and  if  originally  not  present  in  larger  quan- 
tity, the  substance  will  now  be  found  free  from  the  impurity,  while 
if  present  in  larger  proportions  than  can  be  removed  by  the  quantity 
of  reagent  added,  the  excess  can  be  detected  by  appropriate  tests. 

If  an  excess  of  impurity  is  thus  discovered,  regardless  of  the  fact 
whether  the  excess  be  large  or  small,  the  substance  examined  does 
not  come  up  to  the  pharmacopoeial  requirements. 

Thus,  in  potassium  bromide,  the  pharmacopoeial  limit  of  potassium  carbon- 
ate is  0.068  per  cent.  In  order  to  determine  whether  or  not  this  limit  is  ex- 
ceeded, the  Pharmacopeia  directs  the  addition  of  0.1  c.c.  of  £  sulphuric  acid 


DETECTION  OF  IMPURITIES.  437 

to  a  solution  of  1  gramme  of  the  salt  in  10  c.c.  of  water.  Since  0.1  c.c.  of  5 
sulphuric  acid  is  capable  of  neutralizing  0.000686  gramme  of  potassium  carbon- 
ate, the  whole  quantity  allowed  would  be  neutralized  by  the  addition  of  the 
prescribed  quantity  of  acid,  and  no  red  tint  should  be  imparted  to  the  heated 
liquid  by  adding  a  few  drops  of  phenolphthalein  solution  ;  a  red  color  would 
indicate  that  more  alkali  carbonate  was  present  in  the  weighed  sample  than 
could  be  neutralized  by  the  quantity  of  acid  added. 

Quantitative  determination  of  the  principal  constituent. 
These  determinations  are  made  in  the  majority  of  cases  volumetric- 
ally,  and  require  no  special  explanation  here,  as  the  methods  have 
been  fully  considered  in  the  previous  chapter.  Gravimetric  methods 
are  used  in  the  determination  of  several  alkaloids  and  also  in  a  few 
other  cases. 

QUESTIONS. — What  are  the  sources  of  the  impurities  found  in  chemical 
preparations  ?  Why  is  it  not  obligatory  to  use  chemically  pure  chemicals  for 
medicinal  purposes  ?  Which  are  the  leading  features  adopted  by  the  U.  S.  P. 
in  the  identification  of  chemical  preparations?  State  the  reasons  why  the 
U.  S.  P.  describes  the  tests  for  impurities  so  minutely.  Why  can  we  not  use 
indiscriminately  either  one  of  a  number  of  reagents  or  tests  by  which  the  pres- 
ence of  the  same  impurity  may  be  indicated  ?  What  is  the  principle  applied 
in  the  methods  of  the  Pharmacopeia  for  the  determination  of  a  permitted 
quantity  of  an  impurity  ?  How  can  we  decide  the  question  whether  a  sample 
of  potassium  acetate  contains  more  than  1  per  cent,  of  potassium  chloride  with- 
out making  a  quantitative  estimation  of  chlorine? 


VI. 

CONSIDERATION  OF  CARBON  COMPOUNDS, 
OR  ORGANIC  CHEMISTRY. 


40.  INTRODUCTORY  REMARKS.    ELEMENTARY  ANALYSIS. 

Definition  of  organic  chemistry.  The  term  organic  chemistry 
was  originally  applied  to  the  consideration  of  compounds  formed  in 
plants  and  in  the  bodies  of  animals,  and  these  compounds  were 
believed  to  be  created  by  a  mysterious  power,  called  "  vital  force/' 
supposed  to  reside  in  the  living  organism. 

This  assumption  was  partly  justified  by  the  failure  of  the  earlier 
attempts  to  produce  these  compounds  by  artificial  means,  and  also  by 
the  fact  that  the  peculiar  character  of  the  compounds,  and  the 
numerous  changes  which  they  constantly  undergo  in  nature,  could 
not  be  sufficiently  explained  by  the  experimental  methods  then 
known,  and  the  laws  then  established. 

It  was  in  accordance  with  these  views  that  a  strict  distinction  was 
made  between  inorganic  and  organic  compounds,  and  accordingly 
between  inorganic  and  organic  chemistry,  the  latter  branch  of  the 
science  considering  the  substances  formed  in  the  living  organism 
and  those  compounds  which  were  produced  by  their  decomposition. 

Since  that  time  it  has  been  shown  that  many  substances  which 
formerly  were  believed  to  be  produced  exclusively  in  the  living 
organism,  under  the  influence  of  the  so-called  vital  force,  can  be 
formed  artificially  from  inorganic  matter,  or  by  direct  combination 
of  the  elements.  It  was  in  consequence  of  this  fact  that  the  theory 
of  the  supposed  "  vital  force,"  by  which  organic  substances  could  be 
formed  exclusively,  had  to  be  abandoned. 

The  first  instance  of  the  preparation  of  an  organic  compound  from  inorganic 
material  occurred  in  1828,  when  Wohler  discovered  that  an  aqueous  solution 
of  ammonium  cyanate,  on  evaporation,  yields  crystals  of  urea.  The  latter  up 

439 


440  CONSIDERATION  OF  CARBON  COMPOUNDS. 

to  that  time  had  been  believed  to  be  formed  in  the  animal  system  exclusively. 
As  potassium  cyanate  may  be  obtained  by  oxidation  of  the  cyanide,  and  as  the 
latter  can  be  made  by  passing  nitrogen  over  a  heated  mixture  of  potassium 
carbonate  and  carbon,  it  follows  that  urea  can  be  made  from  the  elements. 

The  conversion  of  ammonium  cyanate  into  urea  is  due  to  a  rearrangement 
of  the  atoms  within  the  molecule,  thus: 


Ammonium  cyanate.  Urea. 

An  organic  compound,  according  to  modern  views,  is  simply  a 
compound  of  carbon  generally  containing  hydrogen,  frequently  also 
oxygen  and  nitrogen,  and  sometimes  other  elements.  As  this  defini- 
tion would  include  carbonic  acid  and  its  salts,  such  as  marble,  CaCO3, 
spathic  iron  ore,  FeCO3,  and  others  —  i.e.9  substances  which  we  are 
accustomed  to  look  upon  as  belonging  to  the  mineral  kingdom  —  it  is 
better  to  omit  carbon  dioxide,  carbonic  acid,  and  carbonates,  and 
define  organic  compounds  as  compounds  containing  carbon  in  a  com- 
bustible form. 

The  definition  usually  given  is  :  Organic  chemistry  is  the  chemistry 
of  the  hydrocarbons  and  their  derivatives.  Hydrocarbons,  as  the  name 
implies,  are  compounds  of  carbon  and  hydrogen,  which  are  to  organic 
chemistry  what  the  elements  are  to  inorganic  chemistry. 

In  a  strictly  systematically  arranged  text-book  of  chemistry  organic  com- 
pounds should  be  considered  in  connection  with  the  element  carbon  itself, 
but  as  these  carbon  compounds  are  so  numerous,  their  composition  often  so 
complicated,  and  the  decompositions  which  they  suffer  under  the  influence  of 
heat  or  other  agents  so  varied,  it  has  been  found  best  for  purposes  of  instruc- 
tion to  defer  the  consideration  of  these  compounds  until  the  other  elements  and 
their  combinations  have  been  studied. 

Elements  entering-  into  organic  compounds.  Organic  com- 
pounds contain  generally  but  a  small  number  of  elements.  These 
are,  besides  carbon,  chiefly  hydrogen,  oxygen,  and  nitrogen,  and 
sometimes  sulphur  and  phosphorus.  Other  elements,  however,  enter 
occasionally  into  organic  compounds,  and  by  artificial  means  all 
metallic  and  non-metallic  elements  may  be  made  to  enter  into  organic 
combinations. 

Here  the  question  presents  itself:  Why  is  it  that  the  four  elements 
carbon,  hydrogen,  oxygen,  and  nitrogen  are  capable  of  producing 
such  an  immense  number  (in  fact,  millions)  of  different  combinations? 
To  this  question  but  one  answer  can  be  given,  which  is  that  these 
four  elements  differ  more  widely  from  each  other,  in  their  chemical 
and  physical  properties,  than  perhaps  any  other  four  elements. 

Carbon  is  a  black,  solid  substance,  which  can  scarcely  be  fused 


INTRODUCTORY  REMARKS.  441 

or  volatilized,  while  hydrogen,  oxygen,  and  nitrogen  are  colorless 
gases  which  can  only  be  converted  into  liquids  with  difficulty.  More- 
over, hydrogen  is  very  combustible,  oxygen  is  a  supporter  of  combus- 
tion, while  nitrogen  is  perfectly  indifferent.  Finally,  hydrogen  is 
univalent,  oxygen  bivalent,  nitrogen  trivalent,  and  carbon  quadri- 
valent. These  elements  are,  therefore,  capable  of  forming  a  greater 
number  and  a  greater  variety  of  compounds  than  would  be  the  case 
if  they  were  elements  of  equal  valence  and  of  similar  properties. 

It  will  be  shown  later  that  carbon  atoms  have,  to  a  higher  degree 
than  the  atoms  of  any  other  element,  the  power  of  combining  with  one 
another  by  means  of  a  portion  of  the  affinities  possessed  by  each  atom, 
thus  increasing  the  possibilities  of  the  formation  of  complex  compounds. 

The  number  of  thoroughly  investigated  organic  compounds  is  estimated  at 
150,000,  and  each  year  is  increased  by  8000  to  9000. 

General  properties  of  organic  compounds.  The  substances 
formed  by  the  union  of  the  four  elements  just  mentioned  have  prop- 
erties in  some  respects  intermediate  to  those  of  their  components. 
Thus,  no  organic  substance  is  as  permanently  solid l  as  carbon,  nor 
as  permanently  gaseous  as  hydrogen,  oxygen,  and  nitrogen. 

Some  organic  substances  are  solids,  others  liquids,  others  gases ; 
generally  they  are  solids  when  the  carbon  atoms  predominate  ;  they 
are  liquids  or  gases  when  the  gaseous  elements,  and  especially  hydro- 
gen, predominate  ;  likewise,  it  may  also  be  said  that  compounds  con- 
taining a  small  number  of  atoms  in  the  molecule  are  gases  or  liquids 
which  are  easily  volatilized ;  they  are  liquids  of  high  boiling- 
points,  or  solids,  when  the  number  of  atoms  forming  the  molecules 
is  large. 

The  combustible  property  of  carbon  and  hydrogen  is  transferred 
to  all  organic  substances,  every  one  of  which  will  burn  when  suffi- 
ciently heated  in  atmospheric  air.  (If  carbon  dioxide,  carbonic  acid 
and  its  salts  be  considered  organic  compounds,  we  have  an  exception 
to  the  rule,  as  they  are  not  combustible.) 

The  properties  possessed  by  organic  compounds  are  many  and 
widely  different.  There  are  organic  acids,  organic  bases,  and  organic 
neutral  substances;  there  are  some  organic  compounds  which  are 
perfectly  colorless,  tasteless,  and  odorless,  while  others  show  every 
possible  variety  of  color,  taste,  and  odor ;  many  serve  as  food,  while 
others  are  most  poisonous ;  in  short,  organic  substances  show  a  greater 
variety  of  properties  than  the  combinations  formed  by  any  other 
four  elements. 

1  Non-volatile  organic  substances  are  decomposed  by  heat  with  generation  of  volatile 
products. 


442  CONSIDERATION  OF  CARBON  COMPOUNDS. 

And  yet,  the  cause  of  all  the  boundless  variety  of  organic  matter 
is  that  peculiar  attraction  called  chemical  affinity,  acting  between  the 
atoms  of  a  comparatively  small  number  of  elements  and  uniting  them 
in  many  thousand  different  proportions. 

It  would,  of  course,  be  entirely  inconsistent  with  the  object  of 
this  book,  if  all  the  many  organic  substances  already  known  (the 
number  of  which  is  continually  being  increased  by  new  discoveries) 
were  to  be  considered,  or  even  mentioned.  It  must  be  sufficient  to 
state  the  general  properties  of  the  various  groups  of  organic  sub- 
stances, to  show  by  what  processes  they  are  produced  artificially  or 
how  they  are  found  in  nature,  how  they  may  be  recognized  and 
separated,  and,  finally,  to  point  out  those  members  of  each  group 
which  claim  a  special  attention  for  one  reason  or  another. 

Difference  in  the  analysis  of  organic  and  inorganic  sub- 
stances. The  analysis  of  organic  substances  differs  from  that  of 
inorganic  substances,  in  so  far  as  the  qualitative  examination  of  an 
organic  substance  furnishes  in  many  cases  but  little  proof  of  the  true 
nature  of  the  substance  (except  that  it  is  organic),  while  the  quali- 
tative analysis  of  an  inorganic  substance  discloses  in  most  cases  the 
true  nature  of  the  substance  at  once. 

For  instance :  If  a  white,  solid  substance,  upon  examination,  be 
found  to  contain  potassium  and  iodine,  and  nothing  else,  the  conclu- 
sion may  at  once  be  drawn  that  the  compound  is  potassium  iodide, 
containing  38.86  parts  by  weight  of  potassium,  and  125.9  parts  by 
weight  of  iodine.  Or,  if  another  substance  be  examined,  and  found 
to  be  composed  of  mercury  and  chlorine,  the  conclusion  may  be  drawn 
that  the  compound  is  either  mercurous  or  mercuric  chloride,  as  no 
other  compounds  containing  these  two  elements  are  known,  and 
whether  the  examined  substance  be  the  lower  or  higher  chloride  of 
mercury,  or  a  mixture  of  both,  can  easily  be  determined  by  a  few 
simple  tests. 

While  thus  the  qualitative  examination  discloses  the  nature  of  the 
substance,  it  is  different  with  organic  compounds.  Many  thousand 
times  the  analysis  might  show  carbon,  hydrogen,  and  oxygen  to  be 
present,  and  yet  every  one  of  the  compounds  examined  might  be 
entirely  different ;  it  is  consequently  not  only  the  quality  of  the  ele- 
ments, but  chiefly  the  quantity  present  which  determines  the  nature 
of  an  organic  substance,  and  in  order  to  identify  an  organic  substance 
with  certainty,  it  frequently  becomes  necessary  to  make  a  quantitative 
determination  of  the  various  elements  present,  and  this  quantitative 
analysis  is  generally  called  ultimate  or  elementary  analysis. 


INTRODUCTORY  REMARKS.  443 

There  are,  however,  for  many  organic  substances  such  character- 
istic tests  that  these  substances  may  be  recognized  by  them  ;  these 
reactions  will  be  mentioned  in  the  proper  places. 

An  analysis  by  which  different  organic  substances,  when  mixed 
together,  are  separated  from  each  other  is  frequently  termed  proximate 
analysis.  Such  an  analysis  includes  the  separation  and  determination 
of  essential  oils,  fats,  alcohols,  sugars,  resins,  organic  acids,  albuminous 
substances,  etc.,  and  is  one  of  the  most  difficult  branches  of  analytical 
chemistry. 

Qualitative  analysis  of  organic  substances.  The  presence  of 
carbon  in  a  combustible  form  is  decisive  in  regard  to  the  organic 
nature  of  a  compound.  If,  consequently,  a  substance  burns  with 
generation  of  carbon  dioxide  (which  may  be  identified  by  passing  the 
gas  through  lime-water),  the  organic  nature  of  this  substance  is 
established.  (See  Chapter  on  Carbon.) 

The  presence  of  hydrogen  can  be  proven  by  allowing  the  gaseous 
products  of  the  combustion  to  pass  through  a  cool  glass  tube,  when 
drops  of  water  will  be  deposited. 

It  is  difficult  to  show  by  qualitative  analysis  the  presence  or 
absence  of  oxygen  in  an  organic  compound,  and  its  determination  is 
therefore  generally  omitted. 

The  presence  of  nitrogen  is  determined  by  heating  the  substance 
with  dry  soda-lime  (a  mixture  of  two  parts  of  calcium  hydroxide  and 
one  part  of  sodium  hydroxide),  when  the  nitrogen  is  converted  into 
ammonia  gas,  which  may  be  recognized  by  its  odor  or  by  its  action 
on  paper  moistened  with  solution  of  cupric  sulphate,  a  dark-blue 
color  indicating  ammonia. 

Ultimate  or  elementary  analysis.  While  the  student  must  be 
referred  to  books  on  analytical  chemistry  for  a  detailed  description  of 
the  apparatus  required  and  the  methods  employed  for  elementary 
analysis,  it  may  here  be  stated  that  the  quantitative  determination  of 
carbon  and  hydrogen  is  generally  accomplished  by  the  following  pro- 
cess :  A  weighed  quantity  of  the  pure  and  dry  substance  is  mixed 
with  a  large  excess  of  dry  cupric  oxide,  and  this  mixture  is  introduced 
into  a  glass  tube,  the  open  end  of  which  is  connected  by  means  of  a 
perforated  cork  and  tubing  with  two  glass  vessels,  the  first  one  of 
which  (generally  a  U-shaped  tube)  is  filled  with  pieces  of  calcium 
chloride,  the  other  (usually  a  tube  provided  with  several  bulbs)  with 
solution  of  potassium  hydroxide.  The  two  glass  vessels,  containing 
the  absorbents  named,  are  weighed  separately  after  having  been 


444  CONSIDERATION  OF  CARBON  COMPOUNDS. 

filled.  Upon  heating  the  combustion-tube  in  a  suitable  furnace,  the 
organic  matter  is  burned  by  the  oxygen  of  the  cupric  oxide,  the 
hydrogen  is  converted  into  water  (steam),  which  is  absorbed  by  the 
calcium  chloride,  and  the  carbon  is  converted  into  carbon  dioxide, 
which  is  absorbed  by  the  potassium  hydroxide.  The  apparatus  repre- 
sented in  Fig.  68  shows  the  gas-furnace  in  which  rests  the  coinbustion- 

FIG.  68. 


Gas-furnace  for  organic  analysis. 

tube  with  calcium  chloride  tube  and  potash  bulb  attached.  Upon 
re-weighing  the  two  absorbing  vessels  at  the  end  of  the  operation,  the 
increase  in  weight  will  indicate  the  quantity  of  water  and  carbon 
dioxide  formed  during  the  combustion,  and  from  these  figures  the 
amount  of  carbon  and  hydrogen  present  in  the  organic  matter  may 
easily  be  calculated. 

For  instance  :  0.81  gramme  of  a  substance  having  been  analyzed, 
furnishes,  of  carbon  dioxide  1.32  gramme,  and  of  water  0.45  gramme. 
As  every  44  parts  by  weight  of  carbon  dioxide  contain  12  parts  by 
weight  of  carbon,  the  above  1.32  gramme  contains  of  carbon  0.36 
gramme,  or  44.444  per  cent.  As  every  17.88  parts  of  water  contain 
2  parts  of  hydrogen,  the  above  0.45  gramme  consequently  contains 
0.0503  gramme,  or  6.213  per  cent. 

Oxygen  is  scarcely  ever  determined  directly,  but  generally  indi- 
rectly, by  determining  the  quantity  of  all  other  elements  and  deduct- 
ing their  weight,  calculated  to  percentages  from  100.  The  difference 
is  oxygen. 

If,  in  the  above  instance,  44.444  per  cent,  of  carbon  and  6.213  per 
cent,  of  hydrogen  were  found  to  be  present,  and  all  other  elements, 


INTRODUCTORY  REMARKS.  445 

except  oxygen,  to  be  absent,  the  quantity  of  oxygen  is,  then,  equal 
to  49.384  per  cent,  and  the  composition  of  the  substance  is  as 
follows : 

Carbon „         .     44.444  per  cent. 

Hydrogen 6.213         " 

Oxygen 49.343 

100.000 

Determination  of  nitrogen.  Nitrogen  is  generally  determined 
by  the  Kjeldahl  method,  which  consists  in  boiling  in  a  suitable  flask  a 
weighed  quantity  of  the  organic  compound  with  30  to  40  times  its 
weight  of  sulphuric  acid  and  a  little  potassium  permanganate  or  mer- 
curic oxide.  By  this  treatment  all  nitrogen  present  is  converted  into 
ammonium  sulphate,  from  which  by  the  addition  of  an  excess  of 
sodium  hydroxide  ammonia  is  liberated.  This  ammonia  is  distilled 
over  into  a  known  volume  of  normal  acid.  By  titration  with  normal 
alkali  the  unsaturated  portion  of  acid  is  determined  and  from  the 
result  the  percentage  of  nitrogen  is  calculated. 

Nitrogen  may  also  be  determined  by  the  Will-  Varr entrap  method,  which  is 
based  on  the  formation  of  ammonia  whenever  nitrogenous  matter  is  heated 
with  soda-lime  (a  mixture  of  sodium  hydroxide  and  calcium  oxide).  The 
method  is  not  applicable  to  all  compounds,  because  the  nitrogen  of  some  is  not 
all  converted  into  ammonia  by  the  process. 

A  third  method,  known  as  the  Dumas  or  absolute  method,  consists  in  oxidiz- 
ing, at  a  red  heat,  the  nitrogenous  substance  by  means  of  cupric  oxide  and 
then  decomposing,  by  means  of  highly-heated  metallic  copper,  any  oxide  of 
nitrogen  which  may  have  been  formed.  By  this  operation  all  nitrogen  is 
obtained  in  the  elementary  state ;  it  is  collected,  measured,  and  from  the  volume 
the  weight  is  calculated. 

For  the  details  of  manipulation  in  the  above  method,  which  are  simply  out- 
lined, large  works  on  quantitative  analysis  must  be  consulted. 

Determination  of  sulphur  and  phosphorus.  These  elements  are 
determined  by  mixing  the  organic  substance  with  sodium  carbonate 
and  nitrate,  and  heating  the  mixture  in  a  crucible.  The  oxidizing 
action  of  the  nitrate  converts  all  carbon  into  carbon  dioxide,  hydrogen 
into  water,  sulphur  into  sulphuric  acid,  phosphorus  into  phosphoric 
acid.  The  latter  two  acids  combine  with  the  sodium  of  the  sodium 
carbonate,  forming  sulphate  and  phosphate  of  sodium.  The  fused 
mass  is  dissolved  in  water,  and  sulphuric  acid  precipitated  by  barium 
chloride  in  the  acidified  solution,  phosphoric  acid  by  magnesium 
sulphate  and  ammonium  hydroxide  and  chloride.  From  the  weight 
of  barium  sulphate  and  magnesium  pyrophosphate  (obtained  by  heat- 
ing the  magnesium  ammonium  phosphate)  the  weight  of  sulphur  and 
phosphorus  is  calculated. 


446  CONSIDERATION  OF  CARBON  COMPOUNDS. 

Determination  of  atomic  composition  from  results  obtained 
by  elementary  analysis.  The  elementary  analysis  gives  the  quan- 
tity of  the  various  elements  present  in  percentages,  and  from  these 
figures  the  relative  number  of  atoms  may  be  found  by  dividing  the 
figures  by  the  respective  atomic  weights.  For  instance  :  The  analysis 
above  mentioned  gave  the  composition  of  a  compound,  as  carbon 
44.444  per  cent,,  hydrogen  6.213  per  cent.,  and  oxygen  49.343  per 
cent.  By  dividing  each  quantity  by  the  atomic  weight  of  the  respec- 
tive element,  the  following  results  are  obtained  : 


11.91 


=  3.731 


La 

15.88 


49'34;   =3.107 


The  figures  3.731,  6.213,  and  3.107  represent  the  relative  number 
of  atoms  present  in  a  molecule  of  the  compound  examined.  In  order 
to  obtain  the  most  simple  proportion  expressing  this  relation,  the 
greatest  divisor  common  to  the  whole  has  to  be  found,  a  task  which 
is  sometimes  rather  difficult  on  account  of  slight  errors  made  in  the 
quantitative  determination  itself.  In  the  above  case,  0.6213  is  the 
greatest  divisor,  which  gives  the  following  results  : 


3.731  6.213  _      .     3.107 


0.6213  '  0.6213  '    0.6213 

The  simplest  numbers  of  atoms  are,  accordingly,  carbon  6,  hydrogen 
10,  oxygen  5,  or  the  composition  is  C6H10O5. 

Empirical  and  molecular  formulas.  A  chemical  formula  is 
termed  empirical  when  it  merely  gives  the  simplest  possible  expression 
of  the  composition  of  a  substance.  In  the  above  case,  the  formula 
C6H10O5  would  be  the  empirical  formula.  It  might,  however,  be 
possible  that  this  formula  did  not  represent  the  actual  number  of 
atoms  in  the  molecule,  which  might  contain,  for  instance,  twice  or 
three  times  the  number  of  atoms  given,  in  which  case  the  true  com- 
position would  be  expressed  by  the  formula  C12H20O10  or  C18H30O15. 

If  it  could  be  proven  that  one  of  the  latter  formulas  is  the  correct 
one,  it  would  be  termed  the  molecular  formula,  because  it  expresses 
not  only  the  numerical  relations  existing  between  the  atoms,  but  also 
the  absolute  number  of  atoms  of  each  element  contained  in  the 
molecule. 


ELEMENTARY  ANALYSIS.  447 

The  best  method  for  determining  the  actual  number  of  atoms  con- 
tained in  the  molecule  is  the  determination  of  the  specific  weight  of 
the  gaseous  compound,  taking  hydrogen  as  the  unit.  For  instance : 
Assume  the  analysis  of  a  liquid  substance  gave  the  following  result : 

Carbon 92.308  per  cent. 

Hydrogen 7-692        " 

100.000 

From  this  result  the  empirical  formula,  CH,  is  deduced  by  apply- 
ing the  method  stated  above.  If  this  formula  were  the  molecular 
formula,  the  density  of  the  vapors  of  the  substance  would,  when  com- 
pared with  hydrogen  (according  to  the  law  of  Avogadro),  be  equal  to 
6.455,  because  a  molecule  of  hydrogen  weighs  2  and  a  molecule  of  the 
compound  CH  weighs  12.91. 

Suppose,  however,  the  density  of  the  gaseous  substance  is  found  to 
be  38.73,  then  the  molecular  formula  would  be  expressed  by  C6H6, 
because  its  molecular  weight  (6  X  11.91  -f  6  X  1)  is  equal  to  77.46, 
which  weight,  when  compared  with  the  molecular  weight  of  hydrogen 
=  2,  gives  the  proportions  77.46  :  2,  or  38.73  : 1. 

Not  all  organic  compounds  can  be  converted  into  gases  or  vapors 
without  undergoing  decomposition,  and  the  determination  of  the 
molecular  formulas  of  such  compounds  has  to  be  accomplished  by 
other  methods.  If  the  substance,  for  instance,  is  an  acid  or  a  base, 
the  molecular  formula  may  be  determined  by  the  analysis  of  a  salt 
formed  by  these  substances.  For  instance  :  The  empirical  formula  of 
acetic  acid  is  CH2O ;  the  analysis  of  the  potassium  acetate,  however, 
shows  the  composition  KC2H3O2,  from  which  the  molecular  formula 
HC2H3O2  is  deduced  for  acetic  acid. 

In  many  cases,  however,  it  is  as  yet  absolutely  impossible  to  give 
with  certainty  the  molecular  formula  of  some  compounds. 

Rational,  constitutional,  structural,  or  graphic  formulas. 
These  formulas  are  intended  to  represent  the  theories  which  have 
been  formed  in  regard  to  the  arrangement  of  the  atoms  within  the 
molecule,  or  to  represent  the  modes  of  the  formation  and  decom- 
position of  a  compound,  or  the  relation  which  allied  compounds  bear 
to  one  another. 

The  molecular  formula  of  acetic  acid,  for  instance,  is  C2H4O2,  but 
different  constitutional  formulas  have  been  used  to  represent  the 
structure  of  the  acetic  acid  molecule. 

Thus,  H.C2H3O2  is  a  formula  analogous  to  H.NO3,  indicating  that 
acetic  acid  (analogous  to  nitric  acid),  is  a  monobasic  acid,  containing 
one  atom  of  hydrogen,  which  can  be  replaced  by  metallic  atoms. 


448  CONSIDERATION  OF  CARBON  COMPOUNDS. 

•  C  H  O.OH1  is  a  formula  indicating  that  acetic  acid  is  composed  of 
two  univalent  radicals  which  may  be  taken  out  of  the  molecule  and 
replaced  by  other  atoms  or  groups  of  atoms.  This  formula  indicates 
also  that  acetic  acid  is  analogous  to  hydroxides,  the  radical  C2H3O 
having  replaced  one  atom  of  hydrogen  in  H2O. 

CH  .CO2Hl  is  a  formula  indicating  that  acetic  acid  is  composed  of 
the  two  compound  radicals,  methyl  and  carboxyl. 

It  may  be  said  finally,  that  quite  a  number  of  other  rational 
formulas  have  been  applied,  or,  at  least,  have  been  proposed  by 
different  chemists  and  at  different  times,  to  represent  the  structure  of 
acetic  acid,  but  it  should  be  remembered  that  these  formulas  are  not 
intended  to  represent  the  actual  arrangement  of  the  atoms  in  space, 
but  only,  as  it  were,  their  relative  mode  of  combination,  showing 
which  atoms  are  combined  directly  and  which  only  indirectly,  that 
is,  through  the  medium  of  others. 

41.    CONSTITUTION,  DECOMPOSITION,   AND   CLASSIFICATION 
OF  ORGANIC  COMPOUNDS. 

Radicals  or  residues.  The  nature  of  a  radical  or  residue  has 
been  stated  already  in  Chapter  8,  but  the  important  part  played  by 
radicals  in  organic  compounds  renders  it  necessary  to  consider  them 
more  fully. 

In  most  compounds  there  is  one  or  several  groups  of  atoms  which  re- 
main unchanged  in  the  various  reactions  to  which  the  compounds  may 
be  submitted.  The  group  behaves  like  a  unit  or  an  element,  although 
it  cannot  exist  in  the  free  state.  Such  groups  are  called  radicals. 


QUESTIONS. — What  is  organic  chemistry,  according  to  modern  views  ?  Men- 
tion the  four  chief  elements  entering  into  organic  compounds,  and  name  the 
elements  which  may  be  made  to  enter  into  organic  compounds  by  artificial 
processes.  State  the  reason  why  the  four  elements,  carbon,  hydrogen,  oxy- 
gen, and  nitrogen,  are  better  adapted  to  form  a  larger  number  of  compounds 
than  most  other  elements.  State  the  general  properties  of  organic  compounds. 
Why  does  a  qualitative  analysis  of  an  organic*com pound,  in  most  cases,  'not 
disclose  its  true  nature?  By  what  test  may  the  organic  nature  of  a  compound 
be  established?  By  what  tests  may  the^  presence  of  carbon,  hydrogen,  and 
nitrogen  be  demonstrated  in  organic  compounds?  State  the  methods  by  which 
the  elements  carbon,  hydrogen,  oxygen,  sulphur,  and  phosphorus  are  deter- 
mined quantitatively.  By  what  general  method  may  a  formula  be  deduced 
from  the  results  of  a  quantitative  analysis  ?  What  is  meant  by  an  empirical, 
molecular,  and  constitutional  formula ;  how  are  they  determined,  and  what  is 
the  difference  between  them  ? 


CONSTITUTION  OF  ORGANIC  COMPOUNDS.  449 

Kadicals  exist  in  organic  and  inorganic  compounds ;  an  inorganic 
radical  spoken  of  heretofore  is  the  water  residue  or  hydroxyl,  OH, 
obtained  by  removal  of  one  atom  of  hydrogen  from  one  molecule  of 
water.  Hydroxyl  does  not  exist  in  the  separate  state,  but  it  exists  in 
hydrogen  dioxide,  H2O2,  or  HO — OH,  and  is  also  a  constituent  of  the 
various  hydroxides,  as,  for  instance,  of  KOH,  Ca(OH)2,  Fe(OH)3,  etc. 

If  one  atom  of  hydrogen  be  removed  from  the  saturated  hydro- 
carbon methane,  CH4,  the  univalent  residue  methyl,  CH3,  is  left, 
which  is  capable  of  combining  with  univalent  elements,  as  in  methyl 
chloride,  CH3C1,  or,  with  univalent  residues,  as  in  methyl  hydroxide, 
CH3OH. 

If  two  atoms  of  hydrogen  be  removed  from  CH4,  the  bivalent  resi- 
due methylene,  CH2,  is  left,  capable  of  forming  the  compounds 
CH2C12,  CH2(OH)2,  etc. 

If  three  atoms  of  hydrogen  be  removed  from  CH4,  the  trivalent 
residue  CH  is  left,  capable  of  combining  with  three  atoms  of  univa- 
lent elements,  as  in  CHC13,  or  with  another  trivalent  radical,  etc. 

Chains.  The  expression,  chain,  designates  a  series  of  multivalent 
atoms  (generally,  but  not  necessarily,  of  the  same  element),  held 
together  by  one  or  more  affinities.  While  such  linkage  of  atoms  into 
chains  occurs  with  a  number  of  elements,  it  appears  that  silicon  and 
carbon  have  a  greater  tendency  to  form  chains  than  other  elements. 

The  linkage  of  carbon  atoms  may  be  represented  thus : 

II  III  I      I     I     I 

_C— C— ,        — C— C— C— ,        — C— C— C— C— ,  etc. 

II  III  till 

The  above  carbon  chains  have  6,  8,  and  10  available  affinities, 
respectively,  which  may  be  saturated  by  the  greatest  variety  of  atoms 
or  radicals.  The  chain  combination  of  carbon,  above  indicated  by  the 
first  three  members  of  a  series,  may,  as  far  as  is  known,  be  continued 
indefinitely.  This  fact,  in  connection  with  the  possibility  of  saturating 
the  other  affinities  with  various  atoms  or  radicals,  indicates  the  almost 
unlimited  number  of  possible  combinations  to  be  formed  in  this  way. 
In  fact,  the  existence  of  such  an  enormous  number  of  carbon  com- 
pounds is  greatly  due  to  the  property  of  carbon  to  form  these  chains. 

It  is  not  always  the  case  that  the  atoms  when  forming  a  chain  are 
united  by  one  affinity  only,  as  above,  but  they  may  be  united  by  two 
or  three  affinities,  as  indicated  by  the  compounds  C2H4  and  C2H2,  the 
graphic  formulas  of  which  may  be  represented  by 

H\          /H 


450  CONSIDERATION  OF  CARBON  COMPOUNDS. 

Finally,  it  is  assumed  that  the  carbon  atoms  are  united  partially 
by  double  and  partially  by  single  union,  as,  for  instance,  in  the  so- 
called  closed  chain  of  C6,  capable  of  forming  the  hydrocarbon  benzene, 
C6H6: 

H 

\CAC/  H\c/ 

ACA  HACAH 

'  i 

A  chain  has  also  been  termed  a  skeleton,  because  it  is  that  part  of  an  organic 
compound  around  which  the  other  elements  or  radicals  arrange  themselves, 
filling  up,  as  it  were,  the  unsaturated  affinities. 

Homologous  series.  This  term  is  applied  to  any  series  of  organic 
compounds  the  terms  or  members  of  which,  preceding  or  following 
each  other,  differ  by  CH2,  Moreover,  the  general  character,  the  con- 
stitution, and  the  general  properties  of  the  members  of  an  homologous 
series  are  similar. 

The  explanation  regarding  the  formation  of  an  homologous  series 
is  to  be  found  in  the  above-described  property  of  carbon  to  form 
chains.  By  saturating,  for  instance,  the  affinities  in  the  open  carbon 
chains  mentioned  above,  we  obtain  the  compounds  CH4,  C2H6,  C3H8, 
C4H10,  etc. 

H  HH  HHH  HHHH 

H-C-H,    H-C-C-H,    H-C-C-C-H,    H-C-C-C-C-H, 

H  HH  HHH  HHHH 

Many  homologous  series  of  various  organic  compounds  are  known, 
as,  for  instance  : 

C  H3  Cl,  C  H4  O,  C  H2  02. 

C2H5  Cl,  C2H6  O,  C2H4  02. 

QA  Cl,  C3H8  O,  C3H6  02. 

C4H9C1,  C4H100,  C4H802. 

c5Hnci,  cjr.A  cjw 

etc.  etc.  etc- 

Substitution  is  a  term  used  for  those  reactions  or  chemical  changes 
which  depend  on  the  replacement  of  an  atom  or  a  group  of  atoms  by 
other  atoms  or  groups  of  atoms.  Substitution  takes  place  in  organic 
or  inorganic  substances,  and  its  nature  may  be  illustrated  by  the  fol- 
lowing instances : 


etc. 


CONSTITUTION  OF  ORGANIC  COMPOUNDS.  451 

K     +    H2O    =    KOH    +    H. 
Potassium.      Water.         Potassium      Hydrogen. 
hydroxide. 

C2H402     +     2C1        :    C2H3C102    +     HC1. 
Acetic  acid.      Chlorine.    Monochloracetic   Hydrochloric 
acid.  "    acid. 

C6H6    +    HN03     =    C6H5N02    +     H2O. 
Benzene.       Nitric  acid.      Nitro-benzene.          Water. 

Derivatives.  This  term  is  applied  to  bodies  derived  from  others 
by  some  kind  of  decomposition,  generally  by  substitution.  Thus, 
nitro-benzene  is  a  derivative  of  benzene;  chloroform,  CHC13,  is  a 
derivative  of  methane,  CH4,  obtained  from  the  latter  by  replacement 
of  three  atoms  of  hydrogen  by  the  same  number  of  atoms  of  chlorine. 

Isomerism.  Two  or  more  substances  may  have  the  same  elements 
in  the  same  proportion  by  weight  (or  the  same  centesimal  composi- 
tion), and  yet  be  different  bodies,  showing  different  properties.  Such 
substances  are  called  isomeric  bodies.  Three  kinds  of  isomerism  are 
distinguished,  viz.,  metamerism,  polyinerism,  and  stereo-isomerism. 

Metamerism.  Substances  are  metameric  when  their  molecules  con- 
tain equal  numbers  of  atoms  of  the  same  elements.  Thus,  cane- 
sugar  and  milk-sugar  have  both  the  composition  C12H22On,  and  yet 
they  have  different  physical  properties,  and  may  be  distinguished  by 
their  solubility  and  by  a  number  of  characteristic  tests. 

The  explanation  given  regarding  this  difference  of  properties  is, 
that  the  atoms  are  arranged  differently  within  the  molecule.  In 
some  cases  this  arrangement  is  as  yet  unknown,  in  other  cases  struc- 
tural or  graphic  formulas  showing  this  atomic  arrangement  may  be 
given. 

For  instance  :  Acetic  acid  and  methyl  formate  both  have  the  com- 
position C2H4O2,  but  the  arrangement  of  the  atoms  (or  the  structure) 
is  very  different,  as  shown  by  the  formulas  : 

Acetic  acid.  Methyl  formate. 

C2HS0\0  CHO\0 

a  0< 


CH3X 

As  another  instance  may  be  mentioned  the  compound  CN2H4O, 
which  represents  either  ammonium  cyanate  or  urea  : 

Ammonium  cyanate.  Urea. 

NH4\0  NHACO 

CN/U  NH2/OU' 

Polymerism.     Substances  are  said  to  be  polymeric  when  they  have 
the  same  centesimal  composition,  but  a  different  molecular  weight,  or. 


452  CONSIDERATION  OF  CARBON  COMPOUNDS. 

in    other   words,  when    one    substance   contains   some   multiple   of 
the  number  of  each  of  the  atoms  contained  in  the  molecule  of  the 

other. 

For  instance,  some  volatile  oils  have  the  composition  C20H32,  which 
is  double  the  number  of  atoms  contained  in  oil  of  turpentine,  C10H16 ; 
acetylene,  C2H2,  is  polymeric  with  benzene,  C6H6,  and  styrene,  C8H8 ; 
formaldehyde,  CH2O,  acetic  acid,  C2H4O2>  lactic  acid,  C3H6O3>  and 
glucose,  C6H12O6,  are  polymeric  compounds. 

Stereo-isomerism.  There  has  long  been  known  a  number  of 
bodies  having  the  same  molecular  and  constitutional  formulas  (i.  e., 
behaving  alike  chemically),  but  which  exhibit  differences  in  prop- 
erties, as,  -for  instance,  in  their  behavior  toward  polarized  light 
and  in  the  form  of  their  crystals.  The  explanation  at  present 
given  of  these  differences  is  based  on  this  assumption  :  that  the  dif- 
ferent atoms  or  radicals  in  combination  with  a  carbon  atom  may 
occupy  toward  it  different  relative  positions,  and  that  actually 
they  do. 

In  order  to  understand  what  is  meant  by  this  statement  we  should 
bear  in  mind  that  we  represent  the  grouping  of  our  atoms  on  the 
flat  surface  of  paper,  while  actually  the  formation  of  molecules  takes 
place  in  space — i.  e.y  in  three  directions.  If  we  assume,  for  instance, 
that  four  different  radicals  are  in  combination  with  a  carbon  atom, 
we  can  well  imagine  that  the  relative  positions  in  which  these  radicals 
are  grouped  around  the  carbon  atom  have  an  influence  on  the  nature 
of  the  compound.  There  are  bodies  which  contain  the  same  elements 
in  the  same  quantities  but  in  which  the  molecular  structures  seem  to 
be  reversed,  precisely  as  they  would  be  if  seen  directly  and  then 
observed  after  reflection  from  a  mirror.  In  fact,  there  are  known 
isomeric  bodies  the  crystals  of  which  seem  to  exhibit  exactly  that 
relation  to  each  other. 

The  term  stereo-isomerism  is,  therefore,  used  for  that  kind  of 
isomerism  found  in  substances  which  contain  apparently  the  same 
radicals,  show  practically  the  same  chemical  behavior  toward  other 
agents,  but  differ  in  certain  physical  properties.  Of  stereo-isomeric 
substances  may  be  mentioned  2  malic  acids,  3  lactic  acids,  4  tartaric 
acids,  etc.  (For  details  of  stereo-isomerism  the  student  is  referred 
to  works  treating  more  fully  on  this  subject.) 

Various  modes  of  decomposition.  The  principal  changes  which 
a  molecule  may  suffer  are  as  follows : 


DECOMPOSITION  OF  ORGANIC  COMPOUNDS.  453 

a.  The  atoms  may  arrange  themselves  differently  within  the  mole- 
cule.    Ammonium  cyanate,  NH4CNO,  is  easily  converted  into  urea, 
CO(NH2)2.     This  is  called  molecular  rearrangement. 

b.  A  molecule  may  split  up  into  two  or  more  molecules.     For 
instance  : 

C6H1206    :   :    2C2H6O      +      2CO2. 
Grape-sugar.          Alcohol.          Carbon  dioxide. 

This  decomposition  is  spoken  of  as  cleavage.  When  cleavage  is 
accompanied  by  the  taking  up  of  the  constituents  of  water  the  change 
is  called  hydrolytic  cleavage  or  hydrolysis.  The  following  reaction 
belongs  to  this  class  : 

C9H9NO3  +  H2O  =  C7H602  +  C2H3NH2O2. 

Hippur'ic  acid.  Benzoic  acid.         Glycocoll. 

c.  Two  molecules,  either  of  the  same  kind,  or  of  different  sub- 
stances, may  unite  directly : 

C2H4    -f     2Br      =      C2H4Br2. 
Ethylene.     Bromine.       Ethylene  bromide. 

d.  Atoms  may  be  removed  from  a  compound  without  replacing 
them  by  other  atoms  : 

C2H60    +    O    =    C2H4O    +    H2O. 
Alcohol.       Oxygen.      Aldehyde.          Water. 

e.  Atoms  may  be  removed  and  replaced  by  others  at  the  same 
time  (substitution)  : 

C2H4O2    +    2C1    =    C2H3C1O2      +      HC1. 

Acetic  acid.      Chlorine.    Monochloracetic      Hydrochloric 
acid.  acid. 

Action  of  heat  upon  organic  substances.  As  a  general  rule, 
organic  bodies  are  distinguished  by  the  facility  with  which  they 
decompose  under  the  influence  of  heat  or  chemical  agents ;  the  more 
complex  the  body  is,  the  more  easily  does  it  undergo  decomposition 
or  transformation. 

Heat  acts  differently  upon  organic  substances,  some  of  which  may 
be  volatilized  without  decomposition,  while  others  are  decomposed 
by  heat  with  generation  of  volatile  products.  This  process  of  heating 
non-volatile  organic  substances  in  such  a  manner  that  the  oxygen  of 
the  atmospheric  air  has  no  access,  and  to  such  an  extent  that  decom- 
position takes  place,  is  called  dry  or  destructive  distillation. 

The  nature  of  the  products  formed  during  this  process  varies  not 
only  with  the  nature  of  the  substance  heated,  but  also  with  the  tem- 
perature applied  during  the  operation.  The  products  formed  by 
destructive  distillation  are  invariably  less  complex  in  composition, 


454  CONSIDERATION  OF  CAftSON  COMPOUNDS. 

that  is,  have  a  smaller  number  of  atoms  in  the  molecule,  than  the 
substance  which  suffered  decomposition ;  in  other  words,  a  complex 
molecule  is  split  up  into  two  or  more  molecules  less  complex  in 
composition. 

Otherwise,  the  products  formed  show  a  great  variety  of  properties ; 
some  are  gases,  others  volatile  liquids  or  solids,  some  are  neutral, 
others  basic  or  acid  substances.  In  most  cases  of  destructive  distilla- 
tion a  non-volatile  residue  is  left,  which  is  nearly  pure  carbon. 

Action  of  oxygen  upon  organic  substances.  Combustion. 
Decay.  All  organic  substances  are  capable  of  oxidation,  which 
takes  place  either  rapidly  with  the  evolution  of  heat  and  light  and  is 
called  combustion,  or  it  takes  place  slowly  without  the  emission  of 
light,  and  is  called  slow  combustion  or  decay.  The  heat  generated 
during  the  decay  of  a  substance  is  the  same  as  that  generated  by 
burning  the  substance ;  but  as  this  heat  is  liberated  in  the  first 
instance  during  weeks,  months,  or  perhaps  years,  its  generation  is  so 
slow  that  it  can  scarcely  be  noticed. 

No  organic  substance  found  or  formed  in  nature  contains  a  suffi- 
cient quantity  of  oxygen  to  cause  the  complete  combustion  of  the 
combustible  elements  (carbon  and  hydrogen)  present;  by  artificial 
processes  such  substances  may,  however,  be  produced,  and  are  then 
either  highly  combustible  or  even  explosive. 

During  common  combustion,  provided  an  excess  of  atmospheric  oxygen  be 
present,  the  total  quantity  of  carbon  is  converted  into  carbon  dioxide,  hydrogen 
into  water,  sulphur  and  phosphorus  into  sulphuric  and  phosphoric  acids,  while 
nitrogen  is  generally  liberated  in  the  elementary  state. 

During  the  process  of  decay  the  compounds  mentioned  above  are  produced 
finally,  although  many  intermediate  products  are  generated.  For  instance :  If 
a  piece  of  wood  be  burnt,  complete  oxidation  takes  place ;  intermediate  pro- 
ducts also  are  formed  chiefly  in  consequence  of  the  destructive  distillation  of 
a  portion  of  the  wood,  but  they  are  consumed  almost  as  fast  as  they  are  pro- 
duced, as  was  mentioned  in  connection  with  the  consideration  of  flame.  Again, 
when  a  piece  of  wood  is  exposed  to  the  action  of  the  atmosphere,  it  slowly 
burns  or  decays.  The  intermediate  products  formed  in  this  case  are  entirely 
different  from  those  produced  during  common  combustion. 

Common  alcohol  has  the  composition  C2H6O ;  in  burning,  it  requires 
six  atoms  of  oxygen,  when  it  is  converted  into  carbon  dioxide  and  water : 
CaH«O    +    60    =    2C03    +    3H2O. 

But  alcohol  may  also  undergo  slow  oxidation,  in  which  case  oxygen 
first  removes  hydrogen,  with  which  it  combines  to  form  water,  while 
at  the  same  time  a  compound  known  as  acetic  aldehyde,  C2H4O,  is 
formed  : 


DECOMPOSITION  OF  ORGANIC  COMPOUNDS.  455 

C2H60    -f    O  C2H40     -f     HaO. 

This  aldehyde,  when  further  acted  upon   by  oxygen,  takes  up  an 
atom  of  this  element,  thereby  forming  acetic  acid  : 

C2H40    +    O    =  :    C2H402 

The  three  instances  given  above  illustrate  the  action  of  oxygen 
upon  organic  substances,  which  action  may  consist  in  a  mere  removal 
of  hydrogen,  in  a  replacement  of  hydrogen  by  oxygen,  or  in  an 
oxidation  of  both  the  carbon  and  hydrogen,  and  also  of  sulphur  and 
phosphorus,  if  they  be  present. 

An  organic  substance,  when  perfectly  dry  and  exposed  to  dry  air 
only,  may  not  suffer  decay  for  a  long  time  (not  even  for  centuries), 
but  in  the  presence  of  moisture  and  air  this  oxidizing  action  takes 
place  almost  invariably. 

Besides  the  slow  oxidation  or  decay  which  all  dead  organic  matter 
undergoes  in  the  presence  of  moisture,  there  is  another  kind  of  slow 
oxidation,  called  respiration,  which  takes  place  in  the  living  animal ; 
this  process  will  be  more  fully  considered  in  the  physiological  part  of 
this  book. 

Fermentation  and  putrefaction.  These  terms  are  applied  to 
peculiar  kinds  of  decomposition,  by  which  the  molecules  of  certain 
organic  substances  are  split  up  into  two  or  more  molecules  of  a  less 
complicated  composition.  These  decompositions  take  place  when 
three  factors  are  simultaneously  acting  upon  the  organic  substance. 
These  factors  are :  presence  of  moisture,  favorable  temperature,  and 
presence  of  a  substance  generally  termed  ferment. 

The  most  favorable  temperature  for  these  decompositions  lies 
between  25°  and  40°  C.  (77°  and  104°  F.),  but  they  may  take  place 
at  lower  or  higher  temperatures.  No  substance,  however,  will  either 
ferment  or  putrefy  at  or  below  the  freezing-point,  or  at  or  above  the 
boiling-point  of  water. 

The  nature  of  the  various  ferments  differs  widely,  and  their  true 
action  cannot,  in  many  cases,  be  explained;  what  we  do  know  is, 
that  the  presence  of  comparatively  small  (often  minute)  quantities  of 
one  substance  (the  ferment)  is  sufficient  to  cause  the  decomposition  of 
large  quantities  of  certain  organic  substances,  the  ferment  itself  suf- 
fering often  no  apparent  change  during  this  decomposition. 

Ferments  have  been  divided  into  two  classes :  1.  Organized  fer- 
ments (sometimes  called  true  ferments),  being  unicellular  living  micro- 
organisms chiefly  of  vegetable  origin.  2.  Soluble  ferments,  unorganized 


456  CONSIDERATION  OF  CARBON  COMPOUNDS. 

ferments,  or  enzymes  (false  ferments)  which  are  in  most  cases  nitro- 
genous substances  closely  related  to  the  proteins. 

This  classification  was  based  on  the  belief  that  the  living  cell  itself 
was  the  acting  agent.  It  has,  however,  been  shown  that  this  view  is 
incorrect  and  that  the  decomposing  influence  exerted  by  these  fer- 
ments is  due  to  some  substance  produced  by  the  living  cell,  from 
which  it  may  be  separated  or  extracted  in  a  more  or  less  pure  condi- 
tion. It  is  consequently  more  in  conformity  with  our  present  views 
to  apply  the  term  enzyme  to  that  agent  which  causes  the  decomposi- 
tion. Enzymes  are  always  products  of  the  cell  action  of  a  living 
organism,  but  this  organism  may  be  a  micro-organism,  such  as  the 
yeast  cell ;  or  it  may  be  a  highly  developed  plant,  such  as  the  almond 
tree  which  produces  emulsine,  an  enzyme  which  decomposes  amyg- 
dalin ;  or  it  may  be  an  animal  or  man,  generating  such  enzymes 
as  ptyalin,  pepsin,  etc.  (Enzymes  will  be  more  fully  considered 
later  on.) 

The  nature  of  the  ferment  generally  determines  the  nature  of  the 
decomposition  which  a  substance  suffers,  or,  in  other  words,  one  and 
the  same  substance  will  under  the  influence  of  one  ferment  decom- 
pose with  liberation  of  certain  products,  while  a  second  ferment 
causes  other  products  to  be  evolved.  Sugar,  for  instance,  under  the 
influence  of  yeast,  is  converted  into  alcohol  and  carbon  dioxide, 
while  under  the  influence  of  certain  other  ferments  it  is  converted 
into  lactic  acid. 

The  difference  between  fermentation  and  putrefaction  is  that  the 
first  term  is  used  in  those  cases  where  the  decomposing  substance 
belongs  to  the  group  of  carbohydrates,  all  of  which  contain  the 
elements  carbon,  hydrogen,  and  oxygen  only,  while  substances  be- 
longing to  the  proteins,  which  contain,  in  addition  to  these  three 
elements,  also  nitrogen  and  sulphur,  undergo  putrefaction.  The  two 
last-named  elements  are  generally  evolved  as  ammonia  or  derivatives 
of  ammonia  and  hydrogen  sulphide,  which  gases  give  rise  to  an 
offensive  odor,  the  putrefying  mass  being  generally  designated  as 
fetid  matter. 

As  a  general  rule  the  oxygen  of  the  air  takes  no  part  in  either  fer- 
mentation or  putrefaction,  but  the  presence  or  absence  of  atmospheric 
air  may  cause  or  prevent  decomposition,  inasmuch  as  the  atmosphere 
is  filled  with  millions  of  bacteria,  which  may  act  as  ferments  when  in 
contact  with  organic  matter  under  favorable  conditions. 


DECOMPOSITION  OP  OttOANlC  COMPOUNDS.  457 

One  of  the  fermentations  in  which  oxygen  takes  part  is  acetic  acid  fermen- 
tation, resulting  in  the  conversion  of  alcohol  into  acetic  acid  by  oxidation. 
This  conversion  may  be  brought  about  by  suitable  oxidizing  agents,  or  even  by 
atmospheric  oxygen,  and  is  then  practically  a  slow  combustion  or  decay.  But 
the  transfer  of  oxygen  may  be  brought  about  by  micro-organisms  and  the  pro- 
cess is  then  defined  as  fermentation. 

Whenever  organic  bodies  (a  dead  animal,  for  instance)  undergo  de- 
composition in  nature,  the  processes  of  fermentation  and  putrefaction 
are  generally  accompanied  by  oxidation  or  decay. 

The  conditions  under  which  a  substance  will  ferment  or  putrefy 
have  been  stated  above,  and  the  non-fulfilment  of  these  conditions 
enables  us  to  prevent  decomposition  artificially. 

Thus,  we  make  use  of  a  low  temperature  in  our  refrigerators  or  by 
cold  storage.  We  expel  water  by  drying  or  by  dehydrating  agents 
such  as  absolute  alcohol.  We  prevent  the  action  of  the  ferments 
either  by  antiseptic  agents  (salt,  carbolic  or  salicylic  acid,  etc.)  which 
are  incompatible  with  organic  life,  or  by  excluding  the  air,  and  with 
it  the  ferments,  by  enclosing  the  substances  in  air-tight  vessels  (glass 
jars,  tin  cans,  etc.),  which,  when  filled,  are  heated  sufficiently  to  destroy 
any  bacteria  which  may  have  been  present. 

Antiseptics  and  disinfectants.  While  the  term  antiseptics  is 
applied  to  those  substances  which  retard  or  prevent  fermentation  and 
putrefaction,  the  term  disinfectants  refers  to  those  agents  actually 
destroying  the  organisms  which  are  the  causes  of  these  decomposi- 
tions. If  we  assume  that  all  infectious  diseases  are  due  to  micro- 
organisms, or  germs  of  various  kinds,  disinfectants  may  be  considered 
as  equivalent  to  germicides.  Disinfectants  are  generally  antiseptics 
also,  but  the  latter  are  not  in  all  cases  disinfectants.  The  solution 
of  a  substance  of  certain  strength  may  act  as  a  disinfectant  and 
antiseptic,  while  the  same  solution  diluted  further  may  act  as  an 
antiseptic  only,  but  not  as  a  disinfectant. 

Deodorizers  are  those  substances  which  convert  the  strongly  smell- 
ing products  of  decomposition  into  inodorous  compounds.  Strong 
oxidizing  agents  are  generally  good  deodorizers,  as,  for  instance, 
chlorine,  potassium  permanganate,  hydrogen  dioxide,  etc.  Among 
the  best  antiseptics  and  disinfectants  are  mercuric  chloride  (a  solution 
of  1  :  500  or  1  :  1000) ;  carbolic  acid  (5  per  cent,  solution) ;  potassium 
permanganate  (5  per  cent,  solution) ;  chlorine  (generally  used  in  the 
form  of  a  4  per  cent,  solution  of  calcium  hypochlorite) ;  formaldehyde, 


458  CONSIDERATION  OF  CARBON  COMPOUNDS. 

used  in  solution  or  as  a  gas ;  hydrogen  peroxide,  salicylic  acid,  boric 
acid,  sulphur  dioxide,  ferrous  or  cupric  sulphate,  alcohol,  chloroform, 
thymol,  etc. 

The  selection  of  a  disinfectant  depends  on  the  respective  conditions.  While 
the  relatively  harmless  salicylic  acid  is  often  used  as  a  preservative  for  articles 
of  food  it  is  the  powerful  but  strongly  poisonous  mercuric  chloride  which  is 
used  externally  in  the  operating  room.  The  surgeon  disinfects  his  hands  by 
first  scrubbing  with  soap  and  water,  immersing  in  a  saturated  solution  of  potas- 
sium permanganate  and  washing  finally  in  solution  of  oxalic  acid.  The  latter 
removes  through  its  deoxidizing  and  dissolving  power  that  portion  of  the  per- 
manganate which  adheres  to  the  hands.  For  the  disinfection  of  rooms  gases^ 
such  as  formaldehyde,  sulphur  dioxide  or  chlorine,  are  indicated.  Instruments 
may  be  disinfected  by  heat  or  by  immersion  in  suitable  solutions. 

The  term  asepsis  refers  to  the  absence  of  living  germs  of  fermentation,  putre- 
faction or  disease,  while  the  term  sterilization  is  used  for  the  process  of  destroy- 
ing all  living  micro-organisms  in  the  object  or  material  operated  on.  Aseptic 
conditions  by  means  of  sterilizing  may  be  brought  about  either  by  the  use  of 
antiseptic  agents  or  by  application  of  heat. 


Action  of  chlorine  and  bromine.  These  two  elements  act  upon 
organic  substances  (similarly  to  oxygen)  in  three  different  ways,  viz., 
they  either  (rarely,  however)  combine  directly  with  the  organic  sub- 
stance, or  remove  hydrogen,  or  replace  hydrogen.  The  following 
equations  illustrate  this  action  : 

C2H4        +        2Br        =        C2H4Br2. 
Ethylene.  Bromine.          Ethylene  bromide. 

C2H60      +      2C1    :  :    G2H40      +      2HC1. 
Ethyl  alcohol.       Chlorine.      Aldehyde.    Hydrochloric  acid. 

C2H402      +      2C1  C2H3C102      +      HC1. 

Acetic  acid.         Chlorine.       Monochloracetic      Hydrochloric 
acid.  acid. 

In  the  presence  of  water,  chlorine  and  bromine  often  act  as  oxidiz- 
ing agents  by  combining  with  the  hydrogen  of  the  water  and  liber- 
ating oxygen ;  iodine  may  act  in  a  similar  manner  as  an  oxidizing 
agent,  but  it  rarely  acts  directly  by  substitution. 

Action  of  nitric  acid.  This  substance  acts  either  by  direct  com- 
bination with  organic  bases  forming  salts,  or  as  an  oxidizing  agent, 
or  by  substitution  of  nitryl,  NO2,  for  hydrogen.  As  instances  of  the 
latter  action  may  be  mentioned  the  formation  of  nitro-benzene  and 
cellulose  nitrate: 


DECOMPOSITION  OF  ORGANIC  COMPOUNDS.  459 

C6H6    +    HN03    =    C6H5N02    +     H2O. 
Benzene.       Nitric  acid.       Nitro-benzene.         Water. 

C6H]005    +     3HN03        :    C6H7«N(V,05    +     3H2O. 
Cellulose.  Nitric  acid.       Cellulose  trinitrate.          Water. 

The  additional  quantity  of  oxygen  thus  introduced  into  the  mole- 
cules renders  them  highly  combustible,  or  even  explosive. 

Action  of  dehydrating-  agents.  Substances  having  a  great 
affinity  for  water,  such  as  strong  sulphuric  acid,  phosphoric  oxide, 
and  others,  act  upon  many  organic  substances  by  removing  from  them 
the  elements  of  hydrogen  and  oxygen,  and  combining  with  the  water 
formed,  while,  at  the  same  time,  frequently  dark  or  even  black  com- 
pounds are  formed,  which  consist  largely  of  carbon.  The  black 
color  imparted  to  sulphuric  acid  by  organic  matter  depends  on  this 
action. 

Action  of  alkalies.  The  hydroxides  of  potassium  and  sodium 
act  in  various  ways  on  organic  substances. 

In  some  cases  substitution  products  are  decomposed : 

C2H5C1        -f        KOH  KC1        -f        C2H5OH. 

Ethyl  chloride.  Potassium  Potassium  Ethyl  alcohol, 

hydroxide.  chloride. 

Salts  are  formed  : 

C2H402     -f    NaOH  -=  NaC2H3O2     +    H2O. 
Acetic  Sodium  Sodium  Water, 

acid.  hydroxide.          acetate. 

Fats  are  decomposed  with  the  formation  of  soap  : 

C3H5(C18H3A)3    +    3NaOH    =    C3H5(OH)3    -f    3NaC18H33O2. 
Oleate  of  glyceryl.    Sodium  hydroxide.        Glycerin.  Sodium  oleate. 

Oxidation  takes  place,  while  hydrogen  is  liberated  : 

C,H6O     -f     KOH    =    KC2H3O2     -f    4H. 

Ethyl  Potassium          Potassium         Hydrogen, 

alcohol.          hydroxide.  acetate. 

From  compounds  containing  nitrogen,  ammonia  is  evolved : 

NH2C2H30    -f     KOH  KC2H302     +    NH3. 

Acetamide.  Potassium          Potassium          Ammonia, 

hydroxide.  acetate. 

Action  of  reducing-  agents.  Deoxidizing  or  reducing  agents, 
especially  hydrogen  in  the  nascent  state,  act  upon  organic  substances 
either  by  direct  combination  : 

C2H4O        +        2H        =       C2H60. 
Acetic  aldehyde.  Ethyl  alcohol. 

or  by  removing  oxygen  (and  also  chlorine  or  bromine)  : 


460  CONSIDERATION  OF  CARBON  COMPOUNDS. 

C7H602    +    2H    =    C7H60     +    H20. 
Benzoic  acid.  Benzole  aldehyde. 

C7H6O        +        2H        =        C7H8O. 
Benzoic  aldehyde.  Benzylic  alcohol. 

In  some  cases  hydrogen  replaces  oxygen  : 

C6H5N02    +    6H    =    C6H5NH2    +    2H2O. 
Nitro-benzene.  Aniline. 

Classification  of  organic  compounds.  There  are  great  diffi- 
culties in  arranging  the  immense  number  of  organic  substances 
properly,  and  in  such  a  manner  that  natural  groups  are  formed  the 
members  of  which  are  similar  in  composition  and  possess  like 
k  properties. 

Various  modes  of  classification  have  been  proposed,  some  of  which, 
however,  are  so  complicated  that  the  beginner  will  find  it  difficult  to 
make  use  of  them.  The  grouping  of  organic  substances  here  adopted, 
while  far  from  being  perfect,  has  the  advantages  of  being  simple, 
easily  understood,  and  remembered. 

1.  Hydrocarbons.     All  compounds   containing  the  two  elements 
carbon  and  hydrogen  only.     For  instance,  CH4,  C6H6,  C10H16,  etc. 

2.  Alcohols.     These    are   hydrocarbon   radicals   in   combination 
with  hydroxyl,  OH.    For  instance,  ethyl  alcohol,  CjH^OH,  glycerin, 
C3Hiii5(OH)3,  etc. 

3.  Aldehydes.     Hydrocarbon    radicals   in   combination   with   the 
radical  COH  ;  they  are  compounds  intermediate  between  alcohols 
and   acids,  or  alcohols  from  which   hydrogen   has   been  removed. 
For  instance  : 

C2H60,  CH3.COH,  C2H402, 

Ethyl  alcohol.  Aldehyde.  Acetic  acid. 

4.  Organic  acids.     Hydrocarbon    radicals   in   combination   with 
carboxyl,  a  radical  having  the  composition   CO2H,  or  compounds 
formed  by  replacement  of  hydrogen  in  hydrocarbons  by  carboxyl. 
Instances  :  Acetic  acid,  CH3CO2H  ;  pyrotartaric  acid,  C3H6(CO2H)2. 

5.  Ethers.     Compounds  formed  from  alcohols  by  replacement  of 
the  hydrogen  of  the  hydroxyl  by  other  hydrocarbon  radicals,  or, 
what  is  the  same,  by  other  alcohol  radicals.     For  instance  : 


Ethyl  alcohol.  Ethyl  ether.          Ethyl-methyl  ether. 

6.   Compound  ethers  or  esters.     Formed  from  alcohols  by  replace- 
ment of  the  hydrogen  of  the  hydroxyl  by  acid  radicals,  or  from  acids 


DECOMPOSITION  OF  ORGANIC  COMPOUNDS.  461 

by  replacement  of  the  hydrogen  of  carboxyl  by  alcoholic  radicals. 
For  instance  : 

Q     .    CH3CO\0  C2H5\0         H\0 

C  C     ~  °     h         ° 


H/        ~  CH3CO/ 
Ethyl  alcohol.        Acetic  acid.  Acetic  ether.          Water. 

The  various  fats  belong  to  this  group  of  compound  ethers. 

7.  Carbohydrates.      (Sugars,    starch,    cellulose,   etc.)     These   are 
compounds  of  carbon,  hydrogen,  and  oxygen,  in  which  the  number 
of  carbon   and  oxygen  atoms  is   the  same,  while  the   number  of 
hydrogen  atoms  is  double  that  of  the  oxygen  atoms.     As  the  hydro- 
gen and  oxygen  are  present  in  the  proportion  to  form  water,  they  are 
hence  called  carbohydrates.     There  are  only  a  few  exceptions  to  the 
above  statement.     Most  carbohydrates  are  capable  of  fermentation, 
or  of  being  easily  converted  into  fermentable  bodies.     Instances  : 
C6H1206,  C6HI005,  etc. 

Glucosides  are  substances  the  molecules  of  which  may  be  split  up 
in  such  a  manner  that  several  new  bodies  are  formed,  one  of  which 
is  sugar. 

8.  Amines  and   amides.     Substances   formed   by   replacement   of 
hydrogen  in  ammonia  by  alcohol  or  acid  radicals.     For  instance  : 
ethyl  amine,  NH2.C2H5,  urea,  N2H4.CO,  etc.     The  alkaloids  belong 
to  this  group. 

9.  Cyanogen  and  its  compounds.    Substances  containing  the  radical 
cyanogen,  CN.     For  instance  :  potassium  cyanide,  KCN. 

10.  Proteins   or   albuminous   substances.      These,   besides   carbon, 
hydrogen,  and  oxygen,  always  contain  nitrogen  and  sulphur,  some- 
times also  other  elements.     Instances  :  albumin,  casein,  fibrin,  etc. 

In  connection  with  each  of  these  groups  have  to  be  considered  the 
derivatives  obtained  from  them  directly  or  indirectly. 

As  all  those  organic  compounds  the  constitution  of  which  has 
been  explained  may  be  looked  upon  as  derivatives  of  either  methane, 
CH4,  or  benzene,  C6H6,  a  separation  of  organic  compounds  is  made 

QUESTIONS.  —  Explain  the  term  residue  or  radical.  What  is  understood  by 
the  expression  chain,  when  used  in  chemistry?  What  are  the  characteristics 
of  an  homologous  series  ?  Give  an  explanation  of  the  terms  isomerism,  meta- 
merism, and  polymerism.  How  does  heat  act  upon  organic  compounds? 
What  is  destructive  distillation?  State  the  difference  between  combustion, 
decay,  fermentation,  and  putrefaction  ;  what  is  the  nature  of  these  processes, 
and  under  what  conditions  do  they  take  place?  How  do  chlorine,  nitric  acid, 
and  alkalies  act  upon  organic  substances  ?  What  is  the  action  of  hydrogen 
and  of  dehydrating  agents  upon  organic  substances  ?  Mention  the  chief 
groups  of  organic  compounds. 


462  CONSIDERATION  OF  CARBON  COMPOUNDS. 

into  two  large  classes,  each  one  embodying  all  the  derivatives  of  one 
of  the  two  hydrocarbons  named.  The  derivatives  of  methane  are 
often  termed  fatty  compounds,  those  of  benzene  aromatic  compounds. 
Methane  derivatives  have  representatives  in  each  one  of  the  above 
ten  groups :  benzene  derivatives  are  missing  in  a  few.  As  far  as 
practicable,  the  two  classes  will  be  considered  separately,  because 
the  properties  of  fatty  and  aromatic  compounds  diifer  so  widely,  in 
some  respects,  that  this  method  of  studying  the  nature  of  carbon 
compounds  is  to  be  preferred. 

42.   HYDROCARBONS  AND  THEIR  HALOGEN   DERIVATIVES. 

Occurrence  in  nature.  Hydrocarbons  are  seldom  derived  from 
animal  sources,  being  more  frequently  products  of  vegetable  life; 
thus,  the  various  essential  oils  (oil  of  turpentine  and  others)  of  the 
composition  C10H16  or  C20H32  are  frequently  found  in  plants. 

Other  hydrocarbons  are  found  in  nature  as  products  of  the  decom- 
position of  organic  matter.  Thus  methane,  CH4,  is  generally  formed 
during  the  decay  of  organic  matter  in  the  presence  of  moisture ;  the 
higher  members  of  the  methane  series  are  found  in  crude  coal-oil. 

Formation  of  hydrocarbons.  It  is  difficult  to  combine  the  two 
elements  carbon  and  hydrogen  directly;  as  an  instance  of  such  direct 
combination  may  be  mentioned  acetylene,  C2H2,  which  is  formed 
when  electric  sparks  pass  between  electrodes  of  carbon  in  an  atmos- 
phere of  hydrogen. 

Many  hydrocarbons  are  obtained  by  destructive  distillation  of 
organic  matter,  and  their  nature  depends  on  the  composition  of  the 
material  used  and  upon  the  degree  of  heat  applied  for  the  decompo- 
sition. Hydrocarbons  may  also  be  obtained  by  the  decomposition 
(other  than  destructive  distillation)  of  numerous  organic  bodies,  such 
as  alcohols,  acids,  amines,  etc.,  and  from  derivatives  of  these  sub- 
stances. 

The  hydrocarbons  found  in  nature  are  generally  separated  from 
other  matter,  as  well  as  from  each  other,  by  the  process  known  as 
fractional  distillation.  As  the  boiling-points  of  the  various  compounds 
differ  more  or  less,  they  may  be  separated  by  carefully  distilling  off 
the  compounds  of  lower  boiling-points,  while  noting  the  temperature 
of  the  vapors  above  the  boiling  liquid  by  means  of  an  inserted  ther- 
mometer, and  changing  the  receiver  every  time  an  increase  of  the 
boiling-point  is  noticed.  This  separation  of  volatile  liquids,  known 
as  fractional  distillation,  is,  however,  not  absolutely  complete,  because 


HYDROCARBONS  AND   THEIR  HALOGEN  DERIVATIVES.    463 


traces  of  substances  having  a  higher  boiling-point  are  simultaneously 
volatilized  with  the  distilling  substance. 


FIG. 


Flasks  arranged  for  fractional  distillation. 

For  fractional  distillation  of  small  quantities  of  liquids  as  well  as 
for  the  determination  of  boiling-points,  flasks  arranged  like  those 
shown  in  Fig.  69  may  be  used. 

Properties  of  hydrocarbons.  There  are  no  other  two  elements 
which  combine  together  in  so  many  proportions  as  carbon  and  hydro- 
gen. Several  hundred  hydrocarbons  are  known,  many  of  which 
form  either  homologous  series  or  are  metameric  or  polymeric. 

Hydrocarbons  occur  either  as  gases,  liquids,  or  solids.  If  the  mole- 
cule contains  not  over  4  atoms  of  carbon,  the  compound  is  generally 
a  gas  at  the  ordinary  temperature ;  if  it  contains  from  4  to  10  or  12 
atoms  of  carbon,  it  is  a  liquid ;  and  if  it  contains  a  yet  higher  number 
of  carbon  atoms,  it  is  generally  a  solid. 

All  hydrocarbons  may  be  volatilized  without  decomposition,  all 
are  colorless  substances,  and  many  have  a  peculiar  and  often  charac- 
teristic odor ;  they  are  generally  insoluble  in  water  but  soluble  in 
alcohol,  ether,  disulphide  of  carbon,  etc. 


464 


CONSIDERATION  OF  CARBON  COMPOUNDS. 


First  member. 
CH4 
C2H4 
C2H2 


In  regard  to  chemical  properties,  it  may  be  said  that  hydrocarbons 
are  neutral  substances,  behaving  rather  indifferently  toward  most 
other  chemical  agents.  Many  of  them  are,  however,  oxidized  by  the 
oxygen  of  the  air,  by  which  process  liquid  hydrocarbons  are  often 
converted  into  solids.  The  action  of  halogens  on  hydrocarbons  will 
be  considered  later  on. 

A  number  of  homologous  series  of  hydrocarbons  are  known,  of 
which  the  following  are  the  most  important : 

General  formula. 

Methane  series  or  paraffins,  CnH2U  +  2 

Ethene  series  or  olefins,  CnH2n 

Eihine  series  or  acetylenes,  CnH2n  _  2 

Terpenes,  CnH2n  _  4  C10H16 

Benzene  series,  CnH2n  -  e  C6He 

Of  the  acetylene  series  and  of  the  terpenes  only  a  few  homologues 
are  known. 

The  univalent  radicals  of  the  members  of  the  methane  series  are  designated 
by  changing  the  termination  ane  to  yl  (methane,  methyl,  CH3!) ;  the  bivalent 
radicals  by  changing  ane  to  ene  (rnethene,  CH2]i) ;  and  the  trivalent  radicals 
by  changing  the  final  e  of  ene  to  yl  (methenyl,  CHU1).  The  derivatives  of  the 
bivalent  radicals  are  indicated  by  the  termination  ylene,  as  methylene  iodide, 
CH2I2. 

i 

Hydrocarbons  of  the  paraffin  or  methane  series.  The  hydro- 
carbons having  the  general  composition  CnH2n  +  2  are  known  as 
paraffins,  the  name  being  derived  from  the  higher  members  of  the 
series  which  form  the  paraffin  of  commerce.  The  following  table 
gives  the  composition,  boiling-points,  etc.,  of  the  first  sixteen  mem- 
bers of  this  series : 


Methane  or  methyl  hydride, 
Ethane  or  ethyl  hydride, 
Propane  or  propyl  hydride, 
Butane  or  butyl  hydride, 
Pentane  or  amyl  hydride, 
Hexane  or  hexyl  hydride, 
Heptane  or  heptyl  hydride, 
Octane  or  octyl  hydride, 
Nonane  or  nonyl  hydride, 
Decane  or  decyl  hydride, 
Undecane  or  undecyl  hydride, 
Dodecane  or  dodecyl  hydride, 
Tridecane  or  tridecyl  hydride, 
Tetradecane  or  tetradecyl  hydride, 
Pentadecane  or  pentadecyl  hydride, 
Hexadecane  or  hexadecyl  hydride, 
etc. 


B.  P. 


Sp.  gr. 


H 


H 


H 


1°C. 

38 

0.628 

70 

0.669 

99 

0.690 

125 

0.726 

148 

0.741 

166 

0.757 

184 

0.766 

202 

0.778 

218 

0.796 

236 

0.809 

258 

0.825 

280 

HYDROCARBONS  AND  THEIR  HALOGEN  DERIVATIVES.    465 

The  above  table  shows  that  the  paraffins  form  an  homologous 
series;  the  first  four  members  are  gases,  most  of  the  others  liquids, 
regularly  increasing  in  specific  gravity,  boiling-point,  viscidity,  and 
vapor  density,  as  their  molecular  weight  becomes  greater. 

The  paraffins  are  saturated  hydrocarbons,  the  constitution  of  which 
has  been  already  explained;  they  are  incapable  of  uniting  directly 
with  monatomic  elements  or  residues,  but  they  easily  yield  sub- 
stitution-derivatives when  subjected  to  the  action  of  chlorine  or  bro- 
mine, hydrogen  in  all  cases  being  given  up  from  the  hydrocarbon. 

Most  of  the  paraffins  are  known  in  two  (or  even  more)  modifications ;  there 
are,  therefore,  other  homologous  series  of  hydrocarbons  of  the  same  composition 
as  the  above  normal  paraffins,  which  show  some  difference  from  the  normal 
paraffins  in  boiling-points  and  other  properties.  In  these  isomeric  paraffins  the 
atoms  are  arranged  differently  from  those  in  the  normal  hydrocarbons,  which 
fact  may  be  proven  by  the  difference  in  decomposition  which  these  substances 
suffer  when  acted  upon  by  chemical  agents. 

No  isomeric  hydrocarbons  of  the  first  three  members  of  the  paraffin  series  are 
known,  which  fact  is  in  accordance  with  our  present  theories.  Assuming  that 
the  quadrivalent  carbon  atoms  exert  their  full  valence,  and  that  they  are  held 
together  by  one  bond  only,  we  can  arrange  the  atoms  in  the  compounds, 
CH4,  C2H6,  and  C3H8,  not  otherwise  than  thus: 

/H 
^H 


In  the  next  compound,  butane,  C4H10,  we  have  two  possibilities  explaining 
the  structure  of  the  molecule,  namely,  these  : 

CEBH3 

C=:H2  C=H3 

(j=tiy  O^=Ii3 — OH — G^^-tl3. 

LH 

L/ — r±3 

Both  these  compounds  are  known,  and  termed  normal  butane  and  isobutane, 
respectively. 

The  next  member,  pentane,  C5H12,  shows  three  possibilities  of  constitution, 
thus: 

C=H3 

C=Ha  CEEH3 

|  C=H3-C-H.  | 

C=H2  |  C=H3— C— C^H, 

C=H2  |  _  O=H3. 

C^5iHj| 

C=H3 

These  compounds  also  are  known.    With  the  higher  members  of  the  paraffins 
the  number  of  possible  isomers  rises  rapidly  according  to  the  law  of  permuta- 
30 


466  CONSIDERATION  OF  CARBON  COMPOUNDS. 

tion,  so  that  we  have  of  the  seventh  member  9,  of  the  tenth  75,  and  of  the 
thirteenth  member  80<>,  possible  isomeric  hydrocarbons. 

Methane,  CH4  (Marsh-gas,  Fire-damp).  This  hydrocarbon  has 
been  spoken  of  in  Chapter  14,  where  it  was  stated  that  it  is  a  color- 
less, combustible  gas,  which  is  formed  by  the  decay  of  organic  matter 
in  the  presence  of  moisture,  during  the  formation  of  coal  in  the 
interior  of  the  earth,  and  by  the  destructive  distillation  of  various 
organic  matters.  Methane  is  of  special  interest,  because  it  is  the 
compound  from  which  thousands  of  other  substances  are  derived.  It 
may  be  made  by  the  action  of  inorganic  substances  upon  one  another; 
for  instance,  by  the  action  of  water  on  aluminum  carbide,  a  compound 
of  the  metal  aluminum,  and  carbon,  A14C3,  the  following  change  tak- 
ing place  : 

A14C3    +    12H20    =  =    3CH4    +    4A1(OH)3. 

Bearing  in  mind  that  aluminum  carbide,  as  well  as  water,  may  be 
obtained  by  direct  union  of  the  elements,  it  is  evident  that  methane 
may  be  formed  indirectly,  by  means  of  the  above  method,  from  the 
elements  carbon  and  hydrogen. 

Experiment  51.  Use  apparatus  shown  in  Fig.  35,  page  87,  omitting  the  bent 
tube  B.  Mix  in  a  mortar  20  grammes  of  sodium  acetate  with  20  grammes  of 
potassium  (or  sodium)  hydroxide  and  30  grammes  of  calcium  hydroxide  ;  fill 
with  this  mixture  the  tube  A,  which  should  be  made  of  glass  fusing  with 
difficulty,  or  of  so-called  "combustion  tubing;"  apply  heat  and  collect  the  gas 
over  water.  The  decomposition  takes  place  thus  : 

NaC2H3O2  +  NaOH  =  NajCOg  +  CH4. 


Ignite  the  gas,  and  notice  that  its  flame  is  but  slightly  luminous.  Mix  some 
of  the  gas  in  a  wide-mouth  cylinder,  of  not  more  than  about  200  c.c.  capacity, 
with  an  equal  volume  of  air  and  ignite.  Eepeat  this  experiment  with  mixtures 
of  one  volume  of  methane  with  2,  4,  6,  8,  and  10  volumes  of  atmospheric  air. 
Which  mixture  is  most  explosive,  and  why  ?  How  many  volumes  of  oxygen 
and  how  many  volumes  of  atmospheric  air  are  needed  for  the  complete  com- 
bustion of  one  volume  of  methane  ? 


Ethane,  C-^Hg,  is  a  constituent  of  natural  gas  and  of  crude  petroleum.  It 
can  be  obtained  from  methane  by  first  replacing  in  it  a  hydrogen  atom  by 
iodine,  when  iodo-methane,  or  methyl-iodide,  CH3I,  is  formed,  which,  when 
acted  on  by  sodium,  is  decomposed  thus: 

CH3I  +  CH3I  +  2Na  =  2NaI  +  C2Hfi. 

This  formation  of  ethane  illustrates  one  of  the  methods  for  producing  by 
synthesis—  i.  e.,  for  building  up—  more  complex  from  simpler  hydrocarbons. 
Another  method,  accomplishing  the  same  result,  depends  on  the  action  of  a 


HYDROCARBONS  AND  THEIR  HALOGEN  DERIVATIVES.    467 

zinc  compound  of  the  radicals  on  the  iodides  of  the  radicals.     The  radicals 
may  be  the  same  or  different  ones;  for  instance: 

Zn(CH3)2        +         2CH3T         =        ZnI2        +        2C2He, 
Zinc  methyl.  Methyl  iodide.  Zinc  iodide.  Ethane. 

Zn(CHs)2        +        2C2H5I        =        ZnI2        -f-        2C3H8. 
Ethyl  iodide.  Propane. 

Coal.  As  methane  is  one  of  the  products  generated  during  the 
formation  of  coal,  it  may  be  well  to  consider  this  process  here  briefly. 

The  various  substances  classed  togther  under  the  name  of  coal  con- 
sist principally  of  carbon,  associated  with  smaller  quantities  of  hydro- 
gen, oxygen,  nitrogen,  sulphur,  and  certain  inorganic  mineral  matters 
which  compose  the  ash.  Coal  is  formed  from  buried  vegetable 
matter  by  a  process  of  decomposition  which  is  partly  a  fermentation, 
partly  a  decay,  and  chiefly  a  slow  destructive  distillation,  the  heat 
for  this  latter  process  being  derived  from  the  interior  of  the  earth,  or 
by  the  decomposition  itself. 

The  principal  constituent  of  the  organic  matter  furnishing  coal  is 
wood  (or  woody  fibre,  cellulose),  and  a  comparison  of  the  composition 
of  this  substance  with  the  various  kinds  of  coal  gradually  formed 
will  help  to  illustrate  the  chemical  change  taking  place : 

Carbon.  Hydrogen.  Oxygen. 

Wood 100  12.18  83.07 

Peat 100  9.85  55.67 

Lignite 200  8.37  42.42 

Bituminous  coal         .        .        .        .100  6.12  21.23 

Anthracite  coal 100  2.84              1.74 

This  table  shows  a  progressive  diminution  in  the  proportions  of 
hydrogen  and  oxygen  during  the  passage  from  wood  to  anthracite. 
These  two  elements  must,  therefore,  be  eliminated  in  some  form  of 
combination  which  allows  them  to  move,  viz.,  as  gases  or  liquids. 
The  gases  formed  are  chiefly  carbon  dioxide  (which  finds  its  way 
through  the  rocks  and  soils  to  the  surface  either  in  the  gaseous  state 
or  after  having  been  absorbed  by  water  in  the  form  of  carbonic  acid 
springs)  and  methane,  known  to  coal-miners  as  fire-damp,  frequently 
causing  the  formation  of  explosive  gas  mixtures  in  the  coal  mines,  or 
escaping,  like  carbon  dioxide,  through  fissures  to  the  surface  of  the 
earth,  where  it  may  be  ignited. 

Natural  gas.  While  methane  and  other  combustible  gases  are 
undoubtedly  formed  during  the  formation  of  coal,  the  gas  mixture 
now  generally  termed  natural  gas  (a  mixture  of  methane,  ethane, 
propane,  hydrogen,  and  a  few  other  gases),  and  used  largely  for 


f  Liquids 
Coal-tar  -! 


470  CONSIDERATION  OF  CARBON  COMPOUNDS. 

B.  P. 

f  Benzene         ....  C6H6  80° 

Toluene          .  .        •  C7H8 

Aniline C6H5NH2  182 

Acetic  acid     .  C2H4O2  117 

Water H2O  100 

Carbolic  acid          .        .        .  C6H6O  188 

Kresylic  acid         .        .        .  C7H8O 

Naphthalene  ....  C10H8  220 

Anthracene    ....  CUH10  360 

Paraffin C16H34  280 

Solid  residue :  Coke,  chiefly  carbon  and  inorganic  matter. 

The  gases  are  purified  by  condensing  ammonia  (and  some  other 
gases)  in  water,  carbon  dioxide  and  hydrogen  sulphide  in  calcium 
hydroxide.  The  following  is  the  composition  of  a  purified  illumi- 
nating gas  obtained  from  cannel-coal : 

Hydrogen 46  volumes. 

Methane 41        " 

Ethene 6 

Carbon  monoxide         ....      4        " 

Carbon  dioxide 2         " 

Nitrogen 1  volume. 

The  poisonous  properties  of  illuminating  gas  are  due  chiefly  to  car- 
bon monoxide,  all  other  constituents  being  more  or  less  harmless. 

Experiment  53.  Use  apparatus  shown  in  Fig.  35,  page  87.  Fill  the  combus- 
tion-tube A  with  sawdust  (almost  any  other  non-volatile  organic  matter  may  be 
used),  apply  heat  and  continue  it  as  long  as  gases  are  evolved.  Notice  that  by 
this  process  of  destructive  distillation  are  formed  a  gas  (or  gas  mixture),  which 
may  be  ignited,  a  dark,  almost  black  liquid  (tar),  which  condenses  in  the  tube 
B,  and  that  a  residue  is  left  which  is  chiefly  carbon.  The  tarry  liquid  shows  an 
acid  reaction,  due  to  acetic  and  other  acids  present. 

Coal-tar,  obtained  as  a  by-product  in  the  manufacture  of  illumi- 
nating gas,  contains,  as  shown  by  the  above  table,  many  valuable  sub- 
stances, such  as  benzene,  aniline,  carbolic  acid,  paraffin,  etc.,  which 
are  separated  from  each  other  by  making  use  of  the  diiference  in  their 
boiling-points  and  specific  gravities,  or  of  their  solubility  or  insolu- 
bility in  various  liquids,  or,  finally,  of  their  basic,  acid,  or  neutral 
properties. 

Unsaturated  hydrocarbons.  The  terms  saturated  and  un- 
saturated  compounds  are  used  for  inorganic  and  organic  substances. 
A  compound  is  said  to  be  unsaturated  when  it  has  the  power  to  enter 
directly  into  combination  with  elements  or  compounds.  Thus,  car- 


HYDROCARBONS  AND   THEIR  HALOGEN  DERIVATIVES.    471 

bon  monoxide  and  phosphorus  trichloride  are  un  saturated,  as  they 
combine  directly  with  a  number  of  substances  ;  for  instance,  with 

chlorine,  thus  : 

CO    +  2C1  =  COC12, 

PC13  +  2C1  =  PC15. 

The  hydrocarbons  of  the  methane  series  are  saturated  ;  they  can- 
not be  made  to  enter  directly  into  combination  with  other  substances, 
because  there  are  no  bonds  left  unprovided  for. 

On  the  other  hand,  we  have  several  homologous  series  of  hydro- 
carbons which  are  unsaturated.  The  olefins  belong  to  this  kind, 
and  the  reason  is  found  in  the  structure  of  the  molecules. 

Looking  at  the  graphic  formulas  of  the  normal  hydrocarbons  of  the  methane 
series  on  page  465,  we  find  all  affinities  completely  saturated.  The  structure 
of  ethylene,  C2H4,  the  first  member  of  the  olefines,  may  be  represented  by  either 
of  the  following  formulas  : 

H   H  H   H 

H—  C—  C—  H 


Each  of  these  representations  shows  that  two  bonds  are  left  unsaturated,  and 
as  certain  considerations  lead  us  to  assume  that  two  hydrogen  atoms  are  in 
combination  with  one  carbon  atom  the  second  representation  is  the  one  agree- 
ing with  our  views.  Instead  of  leaving  the  affinities  unsaturated  in  our  for- 
mulas as  above,  we  use  double  linkage,  and  give  to  ethylene  the  formula 

H  H 
H—  C=C—  H  or  H3C=CH2. 

Whenever  direct  combination  between  ethylene  and  another  substance 
occurs  the  double  linkage  is  broken  and  the  bonds  are  utilized  for  holding 

the  respective  atoms,  or  radicals,  thus  : 

Br  Br 

H2C=CH2  +  2Br    =    H2C—  CH2. 

As  the  higher  members  of  the  ethylene  series  are  obtained  by  replacement 
of  hydrogen  atoms  by  hydrocarbon  radicals  in  ethylene,  which  replacement 
does  not  alter  the  double  linkage  of  its  carbon  atoms,  all  members  behave  like 
unsaturated  compounds. 

In  a  similar  manner  we  represent  the  unsaturated  hydrocarbon  acetylene 
C2H2,  by  the  formula  HC=CH,  showing  triple  linkage  between  the  carbon 
atoms.  That  this  view  is  in  keeping  with  the  facts  is  shown  by  the  action  of 
bromine  or  of  hydrobromic  acid  on  acetylene,  thus  : 

HC=CH  +  4Br      =  Br2HC—  CHBr^ 
HfeCH  +  2HBr  =  BrH2C—  CH3Br. 


Coal-tar  - 

Solids 


470  CONSIDERATION  OF  CARBON  COMPOUNDS. 

B.  P. 

f  Benzene          ....    C6H6  80° 

I  Toluene          .                 .        .     C7H8  110 

Liquids     -j   Aniline C6H5NH2  182 

'  Acetic  acid     ....     C2H4O2  117 

Water H2O  100 

Carbolic  acid          .        .        .    C6H6O  188 

Kresylicacid          .        .        .     C7H8O  201 

Naphthalene  ....     CIOH8  220 

Anthracene    ....     CUH10  360 

I  Paraffin C16H34  280 

Solid  residue :  Coke,  chiefly  carbon  and  inorganic  matter. 

The  gases  are  purified  by  condensing  ammonia  (and  some  other 
gases)  in  water,  carbon  dioxide  and  hydrogen  sulphide  in  calcium 
hydroxide.  The  following  is  the  composition  of  a  purified  illumi- 
nating gas  obtained  from  cannel-coal : 

Hydrogen 46  volumes. 

Methane 41        " 

Ethene 6        " 

Carbon  monoxide          ....  4        " 

Carbon  dioxide 2         " 

Nitrogen 1  volume. 

The  poisonous  properties  of  illuminating  gas  are  due  chiefly  to  car- 
bon monoxide,  all  other  constituents  being  more  or  less  harmless. 

Experiment  53.  Use  apparatus  shown  in  Fig.  35,  page  87.  Fill  the  combus- 
tion-tube A  with  sawdust  (almost  any  other  non-volatile  organic  matter  may  be 
used),  apply  heat  and  continue  it  as  long  as  gases  are  evolved.  Notice  that  by 
this  process  of  destructive  distillation  are  formed  a  gas  (or  gas  mixture),  which 
may  be  ignited,  a  dark,  almost  black  liquid  (tar),  which  condenses  in  the  tube 
B,  and  that  a  residue  is  left  which  is  chiefly  carbon.  The  tarry  liquid  shows  an 
acid  reaction,  due  to  acetic  and  other  acids  present. 

Coal-tar,  obtained  as  a  by-product  in  the  manufacture  of  illumi- 
nating gas,  contains,  as  shown  by  the  above  table,  many  valuable  sub- 
stances, such  as  benzene,  aniline,  carbolic  acid,  paraffin,  etc.,  which 
are  separated  from  each  other  by  making  use  of  the  difference  in  their 
boiling-points  and  specific  gravities,  or  of  their  solubility  or  insolu- 
bility in  various  liquids,  or,  finally,  of  their  basic,  acid,  or  neutral 
properties. 

Unsaturated  hydrocarbons.  The  terms  saturated  and  un- 
saturated compounds  are  used  for  inorganic  and  organic  substances. 
A  compound  is  said  to  be  unsaturated  when  it  has  the  power  to  enter 
directly  into  combination  with  elements  or  compounds.  Thus,  car- 


HYDROCARBONS  AND   THEIR  HALOGEN  DERIVATIVES.    471 

bon  monoxide  and  phosphorus  trichloride  are  unsaturated,  as  they 
combine  directly  with  a  number  of  substances ;  for  instance,  with 
chlorine,  thus : 

CO    -f  2C1  =  COC12, 

PC13  +  2C1  =  PC15. 

The  hydrocarbons  of  the  methane  series  are  saturated  ;  they  can- 
not be  made  to  enter  directly  into  combination  with  other  substances, 
because  there  are  no  bonds  left  unprovided  for. 

On  the  other  hand,  we  have  several  homologous  series  of  hydro- 
carbons which  are  unsaturated.  The  olefins  belong  to  this  kind, 
and  the  reason  is  found  in  the  structure  of  the  molecules. 

Looking  at  the  graphic  formulas  of  the  normal  hydrocarbons  of  the  methane 
series  on  page  465,  we  find  all  affinities  completely  saturated.  The  structure 
of  ethylene,  C2H4,  the  first  member  of  the  olefines,  may  be  represented  by  either 
of  the  following  formulas  : 

H   H  H   H 

H— C— C—  H— C— C— H 

A1  '  ' 

Each  of  these  representations  shows  that  two  bonds  are  left  unsaturated,  and 
as  certain  considerations  lead  us  to  assume  that  two  hydrogen  atoms  are  in 
combination  with  one  carbon  atom  the  second  representation  is  the  one  agree- 
ing with  our  views.  Instead  of  leaving  the  affinities  unsaturated  in  our  for- 
mulas as  above,  we  use  double  linkage,  and  give  to  ethylene  the  formula 

H  H 
H— C=C— H  or  HaC=CHr 

Whenever  direct  combination  between  ethylene  and  another  substance 
occurs  the  double  linkage  is  broken  and  the  bonds  are  utilized  for  holding 

the  respective  atoms,  or  radicals,  thus : 

Br  Br 

H2C=CH2  -f  2Br    =    H2C— CH3. 

As  the  higher  members  of  the  ethylene  series  are  obtained  by  replacement 
of  hydrogen  atoms  by  hydrocarbon  radicals  in  ethylene,  which  replacement 
does  not  alter  the  double  linkage  of  its  carbon  atoms,  all  members  behave  like 
unsaturated  compounds. 

In  a  similar  manner  we  represent  the  unsaturated  hydrocarbon  acetylene 
C2H2,  by  the  formula  HfeCH,  showing  triple  linkage  between  the  carbon 
atoms.  That  this  view  is  in  keeping  with  the  facts  is  shown  by  the  action  of 
bromine  or  of  hydrobromic  acid  on  acetylene,  thus  : 

HfeCH  +  4Br      =  Br2HC— CHBry 
2HBr  =  BrH2C— CH8Br. 


472  CONSIDERATION  OF  CARBON  COMPOUNDS. 

Olefins.  The  hydrocarbons  of  the  general  formula  CnH2n  are 
termed  olefins.  To  this  series  belong : 

Ethylene  or  ethene C2H4. 

Propylene  or  propene       ....  C3H6. 

Butylene  or  butene C4H8. 

Amylene  or  pentene          ....  C5H10. 

Hexylene  or  hexene         ....  C6H12. 

Methene,  CH2,  the  lowest  term  of  this  series,  is  not  known.  The 
hydrocarbons  of  this  series  are  not  only  homologous,  but  also  poly- 
meric with  one  another. 

Ethylene,  C2H4  (Ethene,  olefiant  gas),  the  first  member  of  the 
olefins,  is  of  special  interest  on  account  of  its  normal  occurrence  in 
illuminating  gas  made  from  coal,  as  also  in  most  common  flames,  the 
luminosity  of  which  depends  largely  on  the  quantity  of  this  compound 
present  in  the  burning  gas. 

Besides  destructive  distillation  there  are  several  reactions  by  which  ethylene 
can  be  obtained.  Of  these  two  are  of  interest.  The  first  one  depends  on  the 
action  of  an  alcoholic  solution  of  potassium  hydroxide  on  ethyl  chloride,  bro- 
mide, or  iodide : 

C2H5Br  +  KOH  =  C2H4  +  KBr  +  H2O. 

This  reaction  shows  the  possibility  of  preparing  an  unsaturated  compound 
of  the  ethylene  series  from  a  saturated  hydrocarbon ;  and  as  the  method  is 
applicable  to  compounds  of  other  classes  it  furnishes  the  means  to  pass  from 
any  saturated  compound  to  the  corresponding  unsaturated  compound  of  the 
ethylene  series. 

The  second  method  for  preparing  ethylene  depends  on  the  dehydrating  action 
of  sulphuric  acid  on  ethyl  alcohol : 

C2H5OH  H20        =        C2H4. 

Ethylene  combines  directly  with  an  equal  volume  of  chlorine  forming  ethy- 
lene dichloride,  C2H4C12,  an  oily  liquid,  whence  the  name  olefiant  gas. 

Amylene,  C5H10.  Of  the  three  isomeric  hydrocarbons  of  the  composition 
C5H10,  two  have  been  used  medicinally.  It  is  especially  the  amylene  of  the 

CH  CH 

composition  Qjj3^>C  =  C<JT  3 — i.  e.,  trimethyl-ethylene — which  has  been  in- 
troduced as  an  anaesthetic  under  the  name  of  pental.  It  is  formed  from  tertiary 
amyl  alcohol  (amylene  hydrate)  by  the  action  of  dehydrating  agents.  It  is  a 
colorless,  very  volatile  liquid,  insoluble  in  water,  but  miscible  in  all  proportions 
with  chloroform,  ether,  and  alcohol.  It  has  a  penetrating  odor,  reminding  of 
mustard  oil. 


HALOGEN  DERIVATIVES  OF  HYDROCARBONS.  473 

Acetylene,  C2H2,  is  the  first  member  of  a  hydrocarbon  series  of 
the  general  composition  CnH2n_2.  It  has  been  stated  before  that 
acetylene  is  formed  by  direct  union  of  the  elements  when  an  electric 
current  passes  between  two  carbon  poles  in  an  atmosphere  of  hydro- 
gen. It  is  also  formed  during  the  incomplete  combustion  of  coal- 
gas,  such  as  takes  place  when  the  flame  of  a  Btinsen  burner  "  strikes 
back  " — i.  e.,  burns  at  the  base  of  the  burner. 

The  method  now  extensively  used  in  the  manufacture  of  acetylene 
for  illuminating  purposes  depends  on  the  decomposition  of  calcium 
carbide  by  water : 

C2Ca  +  H2O  =  CaO  +  C2H2. 

Pure  acetylene  is  a  gas  of  agreeable  ethereal  odor,  while  the  gas  as  ordi- 
narily prepared  possesses  an  unpleasant  odor,  due  to  impurities.  With  an 
ordinary  burner  acetylene  burns  with  a  luminous  but  sooty  flame,  while  by 
the  use  of  specially  constructed  burners  flames  may  be  obtained  giving  a  very 
pure,  intensely  luminous  white  light.  Like  ethene,  it  combines  directly  with 
halogens,  and  when  heated  to  a  sufficiently  high  temperature  it  is  converted 
into  the  polymeric  compounds,  benzene,  C6H6,  and  styrene,  C8H8. 

A  characteristic  property  of  acetylene  is  the  readiness  with  which  its 
hydrogen  may  be  replaced  by  metals ;  thus,  by  treating  acetylene  with  sodium, 
either  monosodium  acetylid,  C2HNa,  or  disodium  acetylid,  C2Na,,  may  be  ob- 
tained. Silver  acetylid,  C2Ag2,  a  white  crystalline  compound,  and  cuprous 
acetylid,  C2Cu2,  a  red  powder,  may  be  obtained  by  passing  the  gas  through 
ammoniacal  solutions  of  silver  and  cuprous  salts,  respectively.  When  dry, 
both  compounds  explode  violently  when  heated,  the  silver  compound  even 
when  rubbed  with  a  glass  rod. 

Halogen  derivatives  of  hydrocarbons. 

Substitution  products.  When  a  mixture  of  methane  and  chlorine 
is  exposed  to  diffused  daylight  chemical  action  takes  place  gradually, 
resulting  in  the  successive  substitution  of  hydrogen  by  chlorine,  thus  : 

CH4  +  2C1  =  CH3C1  +  HC1. 
CH3C1  +  2C1  =  CH2C12  +  HC1. 
CH2C12  +  2C1  ==  CHC13  +  HC1. 
CHC13  +  2C1  =  CC14  +  HC1. 

These  reactions  between  methane  and  chlorine  are  more  or  less 
characteristic  of  the  general  interaction  between  the  halogens  and 
hydrocarbons,  most  of  the  latter  being  very  susceptible  to  the  action 
of  halogens.  The  4  substitution  products  formed  are  designated 
respectively  as  monochlor-methane  or  chlor-methane,  dichlor-methane, 
trichlor-methane,  and  tetracUor-methane  or  carbon  tetmcMoride.  These 
compounds  may  also  be  looked  upon  as  chlorides  of  the  radicals  CH3', 


474  CONSIDERATION  OF  CARBON  COMPOUNDS. 

methyl ;  CH2H,  methylene  ;  CHm,  meihenyl ;  and  of  carbon  CUii.  The 
univalent  radicals  such  as  methyl,  ethyl,  propyl  are  called  alkyl  or 
alcohol  radicals,  while  the  term  alkylene  designates  bivalent  radicals 
such  as  methylene,  ethylene,  propylene,  etc. 

A  characteristic  feature  of  these  halogen  derivatives  is  the  behavior  of  the 
halogens  towards  such  reagents  as  silver  nitrate.  Chlorine  and  iodine  when  in 
combination  with  hydrogen  or  metals  readily  form  with  a  soluble  silver  salt 
insoluble  chloride  or  iodide.  The  halogens  which  have  replaced  hydrogen  in 
organic  compounds  are,  as  a  general  rule,  not  affected  by  silver  salts  in  solu- 
tion. This  behavior  shows  that  the  substitution  products  are  not  dissociable 
— i.  e.,  there  are  no  halogen  ions  present.  While  above  a  general  method  has 
been  given  by  which  the  halogen  compounds  can  be  made,  there  are  usually 
employed  other  processes  for  their  manufacture.  Also  the  names  given  above 
are  not  always  those  in  general  use.  Thus,  trichlor-methane  or  methenyl 
chloride  is  generally  called  chloroform  and  the  corresponding  bromine  and 
iodine  compounds  bromoform  and  iodoform. 

Methyl  chloride,  CH3C1  (Monochlor-methane),  is  readily  obtainable  by  the 
action  of  hydrochloric  acid  on  methyl  alcohol : 

CH3OH  +  HC1  =  CH3C1  +  H2O. 

It  is  a  colorless,  inflammable  gas  which  can  be  liquefied  by  pressure.  This 
liquid  which  produces  an  intense  cold  by  its  evaporation  has  been  used  locally 
for  neuralgia. 

Dichlor-methane,  CH2C12  (Methylene  chloride),  is  obtained  by  the  action  of 
nascent  hydrogen  on  chloroform  : 

CHC13  +  2H  =  CH8Cla  +  HC1. 

It  is  a  colorless,  oily  liquid,  boiling  at  40°  C.  (104°  F.) ;  sp.  gr.  1.344.  It  has 
an  odor  similar  to  that  of  chloroform,  and  has  been  employed  as  an  anaesthetic. 

Tetrachlor-methane,  CC14  (Carbon  tefrachloride),  is  obtained  by  the  action 
of  chlorine  on  carbon  disulphide,  or  by  treating  chloroform  with  iodine  chloride : 

CH.CL,  -f  IC1  =  CC14  +  HI. 

It  is  a  colorless  liquid  possessing  anaesthetic  properties,  but,  like  the  previous 
compound,  is  dangerous. 

By  far  the  most  important  halogen  derivatives  of  methane  are  the 
trisubstitution  products  :  chloroform,  bromoform  and  iodoform.  The 
gaseous  chlorine  and  the  liquid  bromine  convert  through  their  sub- 
stitution the  gaseous  methane  into  colorless,  heavy,  volatile  liquids, 
while  the  solid  iodine  confers  the  solid  state  upon  the  compound. 

Chloroform,  Chloroformum,  CHOI,  =  118.45  (Trichlor-methane), 
is  obtained  by  the  action  of  bleaching-powder  and  calcium  hydroxide 


HALOGEN  DERIVATIVES  OF  HYDROCARBONS.  475 

on  alcohol.  The  three  substances  named,  after  being  mixed  with  a 
considerable  quantity  of  water,  are  heated  in  a  retort  until  distilla 
tion  commences  ;  the  crude  product  of  distillation  is  an  impure  chloro- 
form, which  is  purified  by  mixing  it  with  strong  sulphuric  acid  and 
allowing  the  mixture  to  stand ;  the  upper  layer  of  chloroform  is 
removed  and  treated  with  sodium  carbonate  (to  remove  any  acids) 
and  distilled  over  calcium  chloride  (to  remove  water). 

A  full  explanation  of  the  formation  of  chloroform  by  the  above  process  will 
be  given  later  on  in  connection  with  the  consideration  of  chloral,  where  it  will 
be  shown  that  alcohol  is  converted  by  the  action  of  chlorine  first  into  aldehyde 
and  subsequently  into  chloral,  which,  upon  being  treated  with  alkalies,  is 
•decomposed  into  an  alkali  formate  and  chloroform. 

The  action  of  the  chlorine  of  the  calcium  hypochlorite  (which  is  the  active 
principle  in  bleaching-powder)  upon  the  alcohol  is  similar  to  that  of  free 
chlorine  upon  alcohol;  in  both  cases  aldehyde,  and  afterward  chloral,  are 
formed,  which  latter,  in  the  manufacture  of  chloroform,  is  decomposed  by  the 
calcium  hydroxide  into  chloroform  and  calcium  formate.  The  last-named  salt 
is,  however,  not  found  in  the  residue  of  the  distillation,  because  it  is  decomposed 
by  bleaching-powder  and  calcium  hydroxide  into  calcium  carbonate,  chloride, 
and  water : 

Ca(CHO2)2  +  Ca(ClO)2  +  Ca(OH)3  =  2CaCO3  +  CaCl2  +  2H2O. 

If  the  various  intermediate  steps  of  the  decomposition  are  not  considered,  the 
process  may  be  represented  by  the  following  equation : 

4C2H60  +  8Ca(C10)2  =  2CHC13  -f  3[Ca(CHO2)2]  +  5CaCl2  +  8H2O. 
Alcohol.  Calcium        Chloroform.  Calcium  Calcium         Water, 

hypochlorite.  formate.  chloride. 

Chloroform  is  now  made  extensively  by  the  action  of  bleaching-powder  upon 
acetone ;  the  reaction  takes  place  thus  : 

2CO(CH3)2  -f  3Ca(C10)2  =  2CHC13  +  2Ca(OH)2  +  Ca(C2H3<V2 
Acetone.  Calcium         Chloroform.         Calcium  Calcium 

hypochlorite.  hydroxide.  acetate. 

Pure  chloroform  is  a  heavy,  colorless  liquid,  of  a  characteristic 
ethereal  odor,  a  burning,  sweet  taste,  and  a  neutral  reaction  ;  it  is  but 
very  sparingly  soluble  in  water,  but  miscible  with  alcohol  and  ether 
in  all  proportions  ;  the  specific  gravity  of  pure  chloroform  is  1.50, 
but  a  small  quantity  of  alcohol  (from  one-half  to  one  per  cent.), 
allowed  to  be  present  by  the  U.  S.  P.,  causes  the  specific  gravity  to 
be  about  1.48;  boiling-point  61°  C.  (141.8°  F.),  but  rapid  evapora- 
tion takes  place  at  all  temperatures. 

Chloroform  or  its  vapors  do  not  ignite  readily,  but  at  a  high  tem- 
perature chloroform  burns  with  a  green  flame.  When  kept  in  a 
partially  filled  bottle  exposed  to  daylight  it  decomposes  with  the  for- 
mation of  the  highly  irritating  carbonyl  chloride  : 


476  CONSIDERATION  OF  CARBON  COMPOUNDS. 

CHC13  +  O  =  COC12  -f-  HC1. 

Chloroform  containing  some  alcohol  is  less  apt  to  undergo  this  oxida- 
tion, but  the  latter  also  takes  place  when  chloroform  is  used  for  inha- 
lation near  an  exposed  flame. 

Analytical  reactions  for  chloroform. 

1.  Dip  a  strip  of  paper  into  chloroform  and  ignite.     The  flame  has 
a  green  mantle  and  emits  vapors  of  hydrochloric  acid,  rendered  more 
visible  upon  the  approach  of  a  glass  rod  moistened  with  ammonia  water. 

2.  Add  a  drop  of  chloroform  and  a  drop  of  aniline  to  some  alco- 
holic solution  of  potassium  hydroxide  and  heat  gently  :  a  peculiar, 
penetrating,  offensive  odor  of   benzo-isonitrile,  C6H5NC,  is  noticed. 
(Chloral  shows  the  same  reaction.) 

CHClg  -f  3KOH  +  C6H5.NH2  =  C6H5NC  +  3KC1  +  3H2O. 

3.  Add  some  chloroform  to   Fehling's   solution  and  heat :    red 
cuprous  oxide  is  precipitated. 

4.  Vapors  of  chloroform,  when  passed  through  a  glass  tube  heated 
to  redness,  are  decomposed  into  carbon,  chlorine,  and  hydrochloric 
acid.     The  two  latter  should  be  passed  into  water,  and  may  be  recog- 
nized by  their  action  on  silver  nitrate  (white  precipitate  of  silver 
chloride)  and  on  mucilage  of  starch,  to  which  potassium  iodide  has 
been  added  (blue  iodized  starch  is  formed). 

5.  Heat  some  chloroform  with  solution  of  potassium  hydroxide  and 
a  little  alcohol.     Chloroform  is  decomposed  into  potassium  chloride 
and  formate : 

CHC13  -f  4KOH  ==  3KC1  +  KCH02  +  2H2O. 

Divide  solution  into  two  portions.  Acidulate  one  portion  with 
nitric  acid,  boil,  and  add  silver  nitrate  :  white  precipitate  of  silver 
chloride.  To  second  portion  add  a  little  ammonia  water  and  a  crystal 
of  silver  nitrate :  a  mirror  of  metallic  silver  will  be  formed  after 
heating  slightly. 

6.  Add  to  1  c.c.  of  chloroform  about  0.3  gramme  of  resorcin  in 
solution,  and  3  drops  of  solution  of  sodium  hydroxide  ;  boil  strongly  : 
a  yellowish-red  color  is  produced,  and  the  liquid  shows  a  beautiful 
yellow-green  fluorescence.     (Chloral  shows  the  same  reaction.) 

In  cases  of  poisoning  chloroform  is  generally  to  be  sought  for  in  the  lungs 
and  blood,  which  are  placed  in  a  flask  connected  with  a  tube  of  difficultly 
fusible  glass.  By  heating  the  flask  the  chloroform  is  expelled  and  decomposed 
in  the  heated  glass  tube,  as  stated  above  in  reaction  4.  Another  portion  of 
chloroform  should  be  distilled  without  decomposing  it,  and  the  distillate  tested 
as  above  stated. 

There  is  no  chemical  antidote  which  may  be  used  in  cases  of  poisoning  by 


HALOGEN  DERIVATIVES  OF  HYDROCARBONS.  477 

chloroform,  and  the  treatment  is,  therefore,  confined  to  the  use  of  the  stomach- 
pump,  to  the  maintenance  of  respiration  with  oxygen  inhalation,  and  to  the 
use  of  strychnine  hypodermically. 

Bromoform,  Bromoformum,  CHBr3  (Tribrom-methane),  is  an 
extremely  heavy,  colorless  mobile  liquid,  with  an  ethereal  odor,  and 
a  penetrating,  sweet  taste,  resembling  chloroform,  specific  gravity 
2.884 ;  B.  P.  148°  C.  It  is  sparingly  soluble  in  water,  soluble  in 
alcohol  and  ether.  Its  physiological  action  is  similar  to  that  of 
chloroform. 

Bromoform  may  be  obtained  by  gradually  adding  bromine  to  a  cold  solution 
of  potassium  hydroxide  in  ethyl  alcohol  until  the  color  is  no  longer  discharged, 
and  rectifying  over  calcium  chloride.  It  is  also  made  by  the  action  of  an  alkali 
hypobromite  on  acetone. 

lodoform,  lodoformum,  CHI3  =  390.61  (Triiodo-methane).  This 
compound  is  analogous  in  its  constitution  to  chloroform  and  bromo- 
form.  It  is  made  by  heating  together  an  aqueous  solution  of  an  alkali 
carbonate,  iodine,  and  alcohol  until  the  brown  color  of  iodine  has 
disappeared ;  on  cooling,  iodoform  is  deposited  in  yellow  scales,  which 
are  well  washed  with  water  and  dried  between  filtering  paper.  (For 
an  explanation  of  the  chemical  changes  taking  place  see  chloral  and 
chloroform.) 

lodoform  occcurs  in  small,  lemon-yellow,  lustrous  crystals,  having 
a  peculiar,  penetrating  odor,  and  an  unpleasant,  sweetish  taste ;  it  is 
nearly  insoluble  in  water  and  acids,  soluble  in  alcohol,  ether,  fatty 
and  essential  oils.  It  contains  96.7  per  cent,  of  iodine. 

lodoform  digested  with  an  alcoholic  solution  of  potassium  hy- 
droxide imparts,  after  acidulation  with  nitric  acid,  a  blue  color  to 
starch  solution.  (See  reaction  in  Test  5  under  Chloroform.) 

Experiment  54.  Dissolve  4  grammes  of  crystallized  sodium  carbonate  in  6 
c.c.  of  water :  add  to  this  solution  1  c.c.  of  alcohol ;  heat  to  about  70°  C.  (158° 
F.),  and  add  gradually  1  gramme  of  iodine.  A  yellow  crystalline  deposit  of 
iodoform  separates. 

Ethyl  chloride,  ^Jthylis  chloridum,  C2H5C1  =  64  (Chlor-cthane), 
is  prepared  analogously  to  methyl  chloride  by  the  action  of  hydro- 
chloric acid  gas  upon  absolute  ethyl  alcohol : 

C2H5OH  +  HC1  =  C2H5C1  +  H20. 
In  place  of  hydrochloric  acid  phosphorus  pentachloride  may  be  used : 

C2H6OH  +  PC15  =  C2H5C1  +  POC1,  +  HCL 

Ethyl  chloride  is  a  gas  at  ordinary  temperature,  but  by  pressure  it 
is  converted  into  a  colorless,  mobile,  very  volatile  liquid  which  boils  at 


478  CONSIDERATION  OF  CARBON  COMPOUNDS. 

12.5°  C.  The  compressed  liquid  is  sold  in  tubes,  from  which  it  is  permit- 
ted to  escape  through  a  small  opening  when  used  as  a  local  anaesthetic. 
It  is  highly  inflammable.  It  is  known  also  as  kelene  or  chelene. 

Ethyl  bromide,  C2H5Br  (Brom-ethane,  Hydrobromlc  ether],  is  obtained  by 
the  same  reactions  as  ethyl  chloride,  substituting  bromine  for  chlorine.  It  is 
a  colorless,  heavy,  volatile  liquid.  Specific  gravity  1.473;  B.  P.  40°  C.  When 
inhaled  it  rapidly  produces  anaesthesia,  followed  by  quick  recovery. 

Somnoform  is  said  to  be  a  mixture  of  60  parts  of  ethyl  chloride,  35  parts  of 
methyl  chloride,  and  5  parts  of  ethyl  bromide.  It  is  used  to  some  extent  in 
dentistry  as  an  anaesthetic. 

Ethyl  iodide,  C2H5I,  may  be  obtained  similarly  to  the  chlorine  or  bromine 
compound.  It  is  a  colorless  liquid  with  the  boiling-point  of  72°  C. 

Compounds  of  hydrocarbon  (alkyl)  radicals  with  other  elements.  Some 
metals,  as  zinc,  magnesium,  cadmium,  aluminum,  etc.,  can  form  compounds 
with  alkyl  radicals;  for  example,  Zn(CH3)2,  Sn(C2H5)4.  Likewise,  alkyl  rad- 
icals can  be  substituted  for  one  or  more  atoms  of  hydrogen  in  ammonia  (NH3), 
arsine  (AsH3),  and  phosphine  (PH3) ;  for  example,  NH.2.CH3,  AsH(CH3)2, 
P(CH3)3.  The  alkyl  derivatives  of  ammonia  are  treated  in  chapter  49.  One 
of  the  arsenic  compounds  possesses  some  interest  because  of  its  use  in  med- 
icine, although  its  employment  is  limited.  When  arsenous  oxide  and  potas- 
sium acetate  are  distilled  together,  a  heavy,  horribly-smelling,  poisonous, 
fuming  oil  is  formed,  the  principal  constituent  of  which  has  the  composition, 
[(CH3)2As]2O.  The  reaction  is,  As2O3  +  4CH3COQK  =  K2C03  +  2CO2  + 
[(CH3)2As]2O.  Dimethyl  arsine  oxide  is  known  best  as  cacodyl  oxide,  the 
word  cacodyl  having  been  adopted  in  allusion  to  the  disgusting  odor  of  the 
compound.  It  contains  the  univalent  radical,  (CH3)2As — ,  which  acts  like  an 
atom  of  a  univalent  metal.  Cacodyl  itself,  (CH3)2As — As(CH3)2,  also  exists. 
The  oxide  has  a  strong  affinity  for  oxygen,  and  inflames  in  oxygen  gas,  but  not 
in  air.  By  oxidizing  cacodyl  oxide  with  mercuric  oxide,  cacodylic  acid  is  formed, 
(CH3)2AsO.OH,  which  yields  odorless  prisms,  easily  soluble  in  water.  Sodium 
cacodylate,  (CH3)2AsO.ONa  -f  3H2O,  also  called  sodium  dimethyl  arsenate,  is 
evidently  closely  related  to  mono-sodium  arsenate.  It  is  a  white  odorless 
powder,  very  soluble  in  water,  forming  needle-shaped  crystals,  which  are  hygro- 
scopic, but  otherwise  very  stable.  The  aqueous  solution  is  alkaline  to  litmus, 
but  nearly  neutral  to  phenolphthalein.  Its  action  is  similar  to  that  of  other 
arsenic  compounds,  but  it  is  said  to  be  much  less  toxic,  and  also  less  apt  to 
cause  undesirable  side-effects. 

QUESTIONS. — How  do  hydrocarbons  occur  in  nature,  and  by  what  processes 
are  they  formed  in  nature  or  artificially?  State  the  general  physical  and 
chemical  properties  of  hydrocarbons.  State  the  composition  and  properties 
of  methane,  and  also  the  conditions  under  which  it  is  formed  in  nature.  What 
is  coal,  what  are  its  constituents,  from  what  is  it  derived,  and  by  what  process 
has  it  been  formed  ?  What  is  crude  coal-oil,  what  is  petroleurn-benzin,  and  wh at 
is  petrolatum?  How  is  illuminating  gas  manufactured,  and  what  are  its  chief 
constituents?  Mention  some  of  the  important  substances  found  in  coal-tar. 
State  of  chloroform :  composition,  properties,  two  processes  for  its  manufacture, 
and  method  of  detection.  Explain  the  action  of  chlorine  on  methane  and 
name  the  products.  How  is  iodoform  made  and  what  are  its  properties  ? 


ALCOHOLS.  479 


43.  ALCOHOLS. 

Constitution  of  alcohols. — The  old  term  "alcohol"  originally 
indicated  but  one  substance  (ethyl  alcohol),  but  it  is  now  applied  to  a 
large  group  of  substances  which  may  be  looked  upon  as  being  derived 
from  hydrocarbons  by  replacement  of  one,  two,  or  more  hydrogen 
atoms  by  hydroxyl,  OH.  In  other  words,  alcohols  are  hydrocar- 
bon radicals  in  combination  with  hydroxyl. 

If  hydroxyl  replaces  but  one  atom  of  hydrogen  in  a  hydrocarbon, 
the  alcohol  is  termed  monatomic  ;  diatomic  and  triatomic  alcohols  are 
formed  by  replacement  of  two  or  three  hydrogen  atoms  respectively. 
(Diatomic  alcohols  are  also  termed  glycols.)  As  an  instance  of  a 
diatomic  alcohol  may  be  mentioned  ethylene  alcohol,  C2H4(OH)2, 
while  glycerin,  C3H5(OH)3,  is  a  triatomic  alcohol.  Tetratomic, 
pentatomic,  and  hexatomic  alcohols  are  also  known. 

It  has  been  shown  before  that  the  higher  members  of  the  paraffin  series  are 
capable  of  forming  a  number  of  isomeric  compounds.  Running  parallel  to  the 
various  series  of  hydrocarbons  (and  their  isomers)  we  have  homologous  series 
of  alcohols.  The  isomeric  alcohols  also  show  properties  different  from  one 
another,  and  yield  different  decomposition  products. 

Normal  alcohols  are  those  with  a  straight  carbon  chain  derived  from  normal 
hydrocarbons.  Alcohols  are  also  divided,  according  to  the  linkage  between  tho 
hydroxyl  groups  and  a  carbon  atom,  into  primary,  secondary,  and  tertiary 
alcohols. 

A  primary  alcohol  is  one  in  which  the  hydroxyl  group  is  linked  to  a  carbon 
atom  which  is  united  to  but  one  other  carbon  atom,  or,  in  other  words,  it  is  one 
containing  the  univalent  group,  — CH2— OH.  For  instance,  ethyl  alcohol, 
CH3— CH2— OH,  represents  a  primary  alcohol.  Primary  alcohols  yield  by 
oxidation  aldehydes  and  acids. 

A  secondary  alcohol  is  one  in  which  the  hydroxyl  group  is  linked  to  a  car- 
bon atom  which  is  joined  to  two  other  carbon  atoms-*. «.,  the  hydroxyl  forms 
a  side  chain  and   the  bivalent  group  characteristic  of  secondary  alc( 
is>CH-OH.    For  instance,  iso-propyl  alcohol,  ggpCH-OH.     Secondary 

alcohols  yield  ketones  by  oxidation. 

A  tertiary  alcohol  is  one  in  which  the  hydroxyl  group  is  linked  to  a  carbon 
atom  which  is  joined  to  three  other  carbon  atoms,  or  one  containing  the  tnva- 

CH3\ 
lent  group  ^C-OH.    For  instance,  tertiary  butyl  alcohol,  CHpC 

tiary  alcohols  by  oxidation  yield  decomposition  products. 

By  saturating  with  hydrogen  the  three  bonds  in  the  above  tnatomic  radical 
methyl  alcohof,  H.O-OH,  is  obtained.  Methyl  alcohol  »  ato  known  as 
carbinol,  and  the  term  carbinoh  is  used  for  the  hydrocarbon  derivative*, 


480  CONSIDERATION  OF  CARBON  COMPOUNDS. 

methyl  alcohol  ;    for  instance,  ethyl  alcohol  may  be  called  methyl-carbinol. 


Alcohols  correspond  in  their  composition  to  the  hydroxides  of 
inorganic  substances  ;  both  classes  of  compounds  containing  hydroxyl, 
OH,  which,  in  the  case  of  alcohols,  is  in  combination  with  radicals 
containing  carbon  and  hydrogen,  in  the  case  of  inorganic  hydroxides 
with  metals,  as,  for  instance,  in  potassium  hydroxide,  KOH. 

If  we  represent  any  hydrocarbon  radical  by  E,  the  general  formula 
of  the  alcohols  will  be  : 

Monatomic  alcohol.  Diatomic  alcohol.  Triatomic  alcohol. 

/OTT  /OH 

Ki—  OH  RJi<^  Riii—  OH 

^OH~  \OH 

or 

Kii(OH)2 


corresponding  to 

KOH  CaW(OH)2  Bim(OH)3. 

Of  the  many  reactions  which  justify  our  views  regarding  the 
structure  of  alcohols,  a  few  may  be  mentioned.  We  believe  that 
hydroxyl  exists  in  metallic  hydroxides,  because  they  can  be  made  by 
the  action  of  metals  on  water,  and  similarly,  by  acting  with  potassium 
on  an  alcohol,  we  obtain  a  potassium  compound  and  free  hydrogen  : 


Also,  when  we  act  on  a  metallic  hydroxide  with  an  acid  a  salt  is 
formed  and  water  produced  ;  the  corresponding  reaction  takes  place 
between  alcohols  and  acids  : 

K.OH  +  HC1  =  KC1  +  H20, 
CH3.OH  +  HC1  =  CH3C1  +  H2O. 

Many  other  reactions  might  be  mentioned  which  furnish  proof 
that  each  oxygen  atom  contained  in  an  alcohol  molecule  is  in  com- 
bination with  an  atom  of  hydrogen—  i.  e.,  that  alcohols  are  hydroxides 
of  hydrocarbon  radicals. 

Occurrence  in  nature.  Alcohols  are  not  found  in  nature  in  a  free 
or  uucombined  state,  but  generally  in  combination  with  acids  as  com- 
pound ethers,  Some  plants,,  for  instance,  contain  compound  ethers 


ALCOHOLS.  481 

mixed  with  volatile  oils.  The  triatomic  alcohol  glycerin  is  a  normal 
constituent  of  all  fats  or  fatty  oils,  and  is  therefore  found  in  many 
plants  and  in  most  animals. 

Formation  of  alcohols.  Alcohols  are  often  produced  by  fermen- 
tation (ethyl  alcohol  from  sugar),  sometimes  by  destructive  distillation 
(methyl  alcohol  from  wood) :  they  are  obtained  from  compound  ethers 
(which  are  compounds  of  acids  and  alcohols)  by  treating  them  with  the 
alkali  hydroxides,  when  the  acid  enters  into  combination  with  the  alkali, 
while  the  alcohols  are  liberated  according  to  the  general  formula : 

RTO>°  +  KOH  = 

Alcohols  may  be  obtained  artificially  by  various  processes,  as,  for 
instance,  by  treating  hydrocarbons  with  chlorine,  when  the  chloride 
of  a  hydrocarbon  residue  is  formed,  which  may  be  decomposed  by 
alkali  hydroxides  in  order  to  replace  the  chlorine  by  hydroxyl,  when 
an  alcohol  is  formed.  For  instance : 

C2H6    +    2C1    ==      C2H5C1      +      HC1. 

Ethane.  Ethyl  chloride. 

C2H5C1    +     KOH  KC1    -f     C2H5OH. 

Ethyl  Potassium      Potassium  Ethyl 

chloride.         hydroxide.       chloride.  alcohol. 

Another  method  by  which  alcohols  can  be  obtained  depends  on 
the  action  of  nitrous  acid  on  amines  containing  radicals  of  the 
methane  series.  For  instance  : 

C2H5NH2   +   NOOH  =  C2H5OH   +   2N  +  H,O. 

Ethyl  amine.        Nitrous  Ethyl 

acid.  alcohol. 

Properties  of  alcohols.  Alcohols  are  generally  colorless,  neutral 
liquids ;  some  of  the  higher  members  are  solids,  none  is  gaseous  at 
the  ordinary  temperature.  Most  alcohols  are  specifically  lighter  than 
water;  the  lower  members  are  soluble  in  or  mix  with  water  in 
all  proportions ;  the  higher  members  are  less  soluble,  and,  finally, 
insoluble.  Most  alcohols  are  volatile  without  decomposition; 
some  of  the  highest  members,  however,  decompose  before  being 
volatilized. 

Although  alcohols  are  neutral  substances,  it  is  possible  to  replace 
the  hydrogen  of  the  hydroxyl  by  metals,  as  has  been  shown  above. 
The  oxygen  of  alcohols  may  be  replaced  by  sulphur,  when  com- 
pounds are  formed  known  as  hydrosulphides  or  mercaptans;  these 
bodies  may  be  obtained  by  treating  the  chlorides  of  hydrocarbon 
radicals  with  potassium  sulphydrate. 

C2H5C1     -f     KSH    =    KC1    + 
31 


482  CONSIDERATION  OF  CARBON  COMPOUNDS. 

By  replacement  of  the  hydrogen  of  the  hydroxyl  in  alcohols  by 
alcohol  radicals  ethers  are  formed ;  by  replacing  the  same  hydrogen 
with  acid  radicals  compound  ethers  are  produced.  Suitable  oxidizing 
agents  convert  alcohols  first  into  aldehydes  then  into  acids. 

Monatomic   normal    alcohols   of    the    general   composition 

or  CnH2n  +  2O. 


Methyl  a 
Ethyl 

Icohol 
u 

.    C  H3OH 
C  H5  OH 

B.  P. 

67°  C. 
78 

Propyl 

« 

C  H  OH 

07 

Butyl 

M 

C4  H9  OH 

115 

Amyl 
Hexyl 

« 
H 

.     C5HUOH 

r  H  OH 

132 
150 

Heptyl 
Octyl 
Nonyl 
Cetyl 
Ceryl 

t( 
U 
it 
« 
It 

.        .     C7H15OH 
.     C8H17OH 
.     C9H19OH 
.        .         .     CKH33OH 
C97H~OH 

168 
186 
204 

50  i 
yg  1   Fusing- 

Melissyl 

u 

85  J     P°int' 

Methyl  alcohol,  CH3OH  (Methyl  hydroxide,  Carbinol,  Wood-spirit, 
Wood-naphtha).  Methyl  alcohol  is  one  of  the  many  products  obtained 
by  the  destructive  distillation  of  wood.  When  pure  it  is  a  thin  color- 
less liquid,  similar  in  odor  and  taste  to  ethyl  alcohol,  and  is  often  sub- 
stituted for  the  latter  for  various  purposes  in  the  arts  and  manu- 
factures. 

Crude  wood-spirit,  which  contains  many  impurities,  has  an  offensive  odor, 
a  burning  taste,  and  is  strongly  poisonous.  A  more  or  less  impure  article  is 
sold  under  the  name  of  Columbian  spirit,  while  methylated  spirit  is  ordinary 
alcohol  containing  10  per  cent,  of  methyl  alcohol. 

The  physiological  intoxicating  and  poisonous  properties  of  methyl  alcohol 
are  similar  to  those  of  ordinary  alcohol,  but  more  pronounced.  Cases  of 
poisoning,  if  recovery  takes  place,  may  be  followed  by  more  or  less  blindness, 
due  to  atrophy  of  the  optic  nerve. 

Ethyl  alcohol,  C2H5OH  =45.7  (Common  alcohol,  Ethyl  hydroxide, 
Spirit),  may  be  obtained  from  ethene,  C2H4,  by  addition  of  the 
elements  of  water,  which  may  be  accomplished  by  agitating  ethene 
with  strong  sulphuric  acid,  when  direct  combination  takes  place  and 
ethyl  sulphuric  acid  is  formed  : 


C2H4        +        H,S04        =        C2H3HS04. 
Ethene.  Sulphuric  acid.        Ethyl  sulphuric  acid. 

Ethyl  sulphuric  acid  mixed  with  water  and  distilled  yields  sul- 
phuric acid  and  ethyl  alcohol  : 

C2H6HS04    +     H20    =    H2SO4    +     C2H5OH. 


ALCOHOLS.  483 

Ethyl  alcohol  may  also  be  obtained,  as  already  mentioned,  by  treat- 
ing ethyl  chloride  with  potassium  hydroxide : 

C2H5C1    +    KOH  KC1    +    C2H6OH. 

While  the  above  methods  for  obtaining  alcohol  are  of  scientific 
interest,  there  is  but  one  mode  of  manufacturing  it  on  a  large  scale, 
namely,  by  the  fermentation  of  certain  kinds  of  sugar,  especially 
grape-sugar  or  glucose,  C6H12O6.  A  diluted  solution  of  grape-sugar 
under  the  influence  of  certain  ferments  (yeast)  suffers  decomposition, 
yielding  carbon  dioxide  and  alcohol : 

C6H1206    =    2CO2    +     2C2H5OH. 
Glucose.  Carbon  Ethyl 

dioxide.  alcohol. 

From  94  to  96  per  cent,  of  the  sugar  is  decomposed,  according  to 
the  above  reaction,  the  rest  forming  glycerin  (3  per  cent.),  succinic 
acid  (0.6  per  cent.),  and  higher  alcohols  designated  "  fusel  oil." 

Experiment  55.  To  a  solution  of  25  grammes  of  commercial  glucose  (grape- 
sugar)  in  1000  c.c.  of  water,  add  a  little  brewer's  yeast  and  introduce  this  mix- 
ture into  a  flask.  Attach  to  the  flask,  by  means  of  a  perforated  cork,  a  bent 
glass  tube  leading  into  clear  lime-water,  contained  in  a  small  flask.  After 
standing  (a  warm  place  should  be  selected  in  winter  for  this  operation)  a  few 
hours  fermentation  will  commence,  which  can  be  noticed  by  the  evolution  of 
carbon  dioxide,  which,  in  passing  through  the  lime-water,  causes  the  precipi- 
tation of  calcium  carbonate. 

After  fermentation  ceases  connect  the  flask  with  a  condenser  and  distil  over 
50  to  100  c.c.  of  the  liquid.  Verify  in  the  distilled  portion  the  presence  of 
alcohol  by  applying  the  tests  mentioned  below.  For  condensation  of  the  dis- 
tilling vapors  a  Liebig's  condenser,  represented  in  Fig.  70,  may  be  used. 

The  alcoholic  strength  of  fermented  sugar  solutions  is  never  over 
14  per  cent.,  since  above  this  point  the  yeast  ceases  to  act.  On  the 
large  scale  this  liquid  is  distilled  in  apparatus  so  arranged  that  the 
vapors  are  repeatedly  condensed  and  vaporized,  thus  yielding  by  a 
single  distillation  an  alcohol  of  about  90  per  cent.  This  is  further 
purified  by  treatment  with  charcoal  and  rectifying  in  so-called  column 
stills,  when  alcohol  containing  as  much  as  94  to  95  per  cent,  is  ob- 
tained. To  remove  the  last  portions  of  water  the  liquid  is  distilled 
over  calcium  oxide,  which  forms  calcium  hydroxide. 

The  alcohol  thus  obtained,  and  containing  not  more  than  1  per 
cent,  of  water,  is  known  as  pure,  absolute,  or  real  alcohol  (alcohol 
absolutum).  The  alcohol  of  the  U.  8.  P.  contains  92.3  per  cent,  by 
weight  or  94.9  per  cent,  by  volume  of  real  alcohol,  and  has  a  specific 
gravity  of  0.816  at  15.6°  C.  (60°  F.).  The  diluted  alcohol,  is  made 
by  mixing  equal  volumes  of  water  and  alcohol,  and  has  a  specific 


484 


CONSIDERATION  OF  CARBON  COMPOUNDS. 


gravity  of  0.936 ;  it  is  identical  with  the  proof-spirit  of  the  U.  8. 
Custom-house  and  Internal  Revenue  service. 

Pure  alcohol  is  a  transparent,  colorless,  mobile,  and  volatile  liquid, 
of  a  characteristic  rather  agreeable  odor,  and  a  burning  taste;  it  boils 
at  78°  C.  (172°  F.),  has  a  specific  gravity  of  0.797,  is  of  a  neutral 
reaction,  becomes  syrupy  at— 110°  C.  (—166°  F.),  and  solidifies  at 
— 130°  C.  ( — 202°  F.);  it  burns  with  a  non-luminous  flame;  when 
mixed  with  water  a  contraction  of  volume  occurs,  and  heat  is  liber- 
ated ;  the  attraction  of  alcohol  for  water  is  so  great  that  strong 
alcohol  absorbs  moisture  from  the  air  or  abstracts  it  from  membranes, 

FIG.  70. 


Liebig's  condenser  with  distilling-flask. 

tissues,  and  other  similar  substances  immersed  in  it;  to  this  property 
are  due  its  coagulating  action  on  albumin  and  its  preservative  action 
on  animal  substances.  The  solvent  powers  of  alcohol  are  very  exten- 
sive, both  for  inorganic  and  organic  substances ;  of  the  latter  it  readily 
dissolves  essential  oils,  resins,  alkaloids,  and  many  other  bodies,  for 
which  reason  it  is  used  in  the  manufacture  of  the  numerous  official 
tinctures,  extracts,  and  fluid  extracts. 

Alcohol  taken  internally  in  a  dilute  form  has  intoxicating  proper- 
ties ;  pure  alcohol  acts  poisonously ;  it  lowers  the  temperature  of  the 
body  from  0.5°  to  2°  C.  (0.9°  to  3.6°  F.),  although  the  sensation  of 
warmth  is  experienced.  Alcohol  is  not  a  food  in  the  ordinary  sense 
of  the  word.  Small  quantities  of  diluted  alcohol  are  oxidized  jn  the 


ALCOHOLS.  485 

system  to  carbon  dioxide  and  water ;  larger  amounts  are  eliminated, 
for  the  most  part  unchanged,  by  the  lungs  and  kidneys. 

The  treatment  of  acute  alcohol  poisoning  is  chiefly  restricted  to  the  evacua- 
tion of  the  stomach,  warm  applications  to  the  extremities,  and  possibly  hypo- 
dermic injections  of  strychnine  to  sustain  the  heart. 

Denatured  alcohol.  Alcohol  may  be  withdrawn  from  bond  without  the 
payment  of  internal  revenue  tax  for  use  in  the  arts  and  industries,  and  for 
fuel,  light,  and  power,  provided  said  alcohol  shall  have  been  mixed,  under 
certain  prescribed  regulations,  with  specified  denaturing  material,  whereby  it  is 
rendered  unfit  for  beverage  or  medicinal  purposes. 

Completely  denatured  alcohol  must  contain  either  methyl  alcohol  and  ben- 
zin,  or  methyl  alcohol  and  pyridine  bases.  Tax-free  alcohol  may  also  be  used 
for  manufacturing  chemicals,  where  the  alcohol  is  changed  into  some  other 
chemical  substance  and  does  not  appear  in  the  finished  product  as  alcohol, 
Inasmuch  as  the  agents  present  in  completely  denatured  alcohol  render  it 
unfit  for  use  in  many  chemical  industries,  special  denaturants  have  been 
authorized  by  the  Commissioner  of  Internal  Revenue  where  absolutely  neces- 
sary. About  fifteen  special  denaturing  formulas  are  in  use  at  the  present  time. 

Hospitals  are  allowed  to  denature  alcohol  with  substances  which  render  it 
unfit  as  a  beverage,  but  not  for  external  use.  For  this  purpose  such  substances 
as  camphor,  thymol,  boric  acid,  etc.,  may  be  used.  . 

For  a  full  account  of  the  subject  of  denatured  alcohol,  and  the  various  for- 
mulas for  this  purpose,  see  the  article  on  Alcohol  in  the  National  Standard 
Dispensatory. 

Analytical  reactions  for  ethyl  alcohol. 

1.  Dissolve  a  small  crystal  of  iodine  in  about  2  c  c.  of  alcohol ; 
add  to  the  cold  solution  potassium  hydroxide  until  the  brown  color 
of  the  solution  disappears ;  a  yellow  precipitate  of  iodoform,  CHI3, 
forms.     Many  other  alcohols,  aldehyde,  acetone,  etc.,  show  the  same 
reaction. 

2.  Add  to  about  1  c.c.  of  alcohol  the  same  volume  of  sulphuric 
acid ;  heat  to  boiling  and  add  gradually  a  little  more  alcohol :  the 
odor  of  ethyl  ether  will  be  noticed  distinctly  on  further  heating. 

3.  Add  to  a  mixture  of  equal  volumes  of  alcohol  and  sulphuric, 
acid,  a  crystal  (or  strong  solution)  of  sodium  acetate:  acetic  ether  is 
formed  and  recognized  by  its  odor. 

4.  To  about  2  c.c.  of  potassium  dichromate  solution  add  0.5  c.c.  of 
sulphuric  acid  and  1  cc.  of  alcohol:  upon  heating  gently  the  liquid 
becomes  green  from  the  formation  of  chromic  sulphate,  while  alde- 
hyde is  formed  and  may  be  recognized  by  its  odor. 

Alcoholic  liquors.  Numerous  substances  containing  sugar  or  starch  (which 
may  be  converted  into  sugar)  are  used  in  the  manufacture  of  the  various  alco- 


486  CONSIDERATION  OF  CARBON  COMPOUNDS. 

holic  liquors,  all  of  which  contain  more  or  less  of  ethyl  alcohol,  besides  color- 
ing matter,  ethers,  compound  ethers,  and  many  other  substances. 

White  and  red  wines  are  obtained  by  the  fermentation  of  the  grape-juice ;  the 
so-called  light  wines  contain  from  10  to  12,  the  strong  wines,  such  as  port  and 
sherry,  from  19  to  25  per  cent,  of  alcohol ;  if  the  grapes  contain  much  sugar, 
only  a  portion  of  it  is  converted  into  alcohol,  while  another  portion  is  left 
undecomposed ;  such  wines  are  known  as  sweet  wines.  Effervescent  wines,  as 
champagne,  are  bottled  before  the  fermentation  is  complete ;  the  carbonic  acid 
is  disengaged  under  pressure  and  retained  in  solution  in  the  liquid. 

Beer  is  prepared  by  fermentation  of  germinated  grain  (generally  barley)  to 
which  much  water  and  some  hops  have  been  added;  the  active  principle  of 
hops  is  lupulin,  which  confers  on  the  beer  a  pleasant,  bitter  flavor,  and  the 
property  of  keeping  without  injury.  Light  beers  have  from  2  to  4,  strong  beers, 
as  porter  or  stout,  from  4  to  6  per  cent,  of  alcohol. 

/Spirits  differ  from  either  wines  or  beers  in  so  far  as  the  latter  are  not  dis- 
tilled, and  therefore  contain  also  non-volatile  organic  and  inorganic  substances, 
such  as  salts,  etc.,  not  found  in  the  spirits,  which  are  distilled  liquids  contain- 
ing volatile  compounds  only.  Moreover,  the  quantity  of  alcohol  in  spirits  is 
very  much  larger,  and  varies  from  45  to  55  per  cent.  Of  distilled  spirits  may 
be  mentioned :  American  whiskey,  made  from  fermented  rye  or  Indian  corn ; 
Irish  whiskey,  from  potatoes ;  Scotch  whiskey,  from  barley ;  brandy  or  cognac,  by 
distilling  French  wines ;  rum,  by  fermenting  and  distilling  molasses ;  gin,  from 
various  grains  flavored  with  juniper  berries. 

Amyl  alcohol,  C5HnOH.  Theoretically  eight  amyl  alcohols  are  possible, 
and  all  are  known.  The  common  amyl  alcohol  is  iso-butyl-carbinol,  (CH3)2.- 
CH.CH2.CH2OH.  It  is  frequently  formed  in  small  quantities  during  the  fer- 
mentation of  corn,  potatoes,  and  other  substances.  When  the  alcoholic  liquors 
are  distilled,  amyl  alcohol  passes  over  toward  the  end  of  the  distillation,  gener- 
ally accompanied  by  propyl,  butyl,  and  other  alcohols,  and  by  certain  ethers 
and  compound  ethers.  A  mixture  of  these  substances  is  known  as  fusel  oil, 
and  from  this  liquid  amyl  alcohol  may  be  obtained  in  a  pure  state.  It  is  an 
oily,  colorless  liquid,  having  a  peculiar  odor  and  a  burning,  acrid  taste ;  it  is 
soluble  in  alcohol,  but  not  in  water.  By  oxidation  of  amyl  alcohol  valerianic 
acid  is  obtained. 

Amylene  hydrate,  Ethyl-dimethyl-carbinol,  (CH3}2.COff.C2H5,  is  an  alcohol 
isomeric  with  the  above  amyl  alcohol,  but  yielding  only  acetic  acid  on  oxida- 
tion. It  is  a  colorless  liquid,  having  a  pungent,  ethereal  odor,  and  a,  boiling- 
point  of  100°  C.  (212°  F.).  It  has  been  used  as  an  hypnotic. 

Allyl  alcohol,  C3H5OH,  is  an  unsaturated  monatomic  alcohol  which  can  be 
obtained  from  glycerin  by  several  reactions.  It  is  most  readily  obtained  by 
distilling  a  mixture  of  glycerin  and  oxalic  acid  between  220°  and  230°  C., 
when  allyl  alcohol,  CH2  =  CH  —  CH2OH,  passes  over.  When  glycerin  is 
treated  with  iodide  of  phosphorus,  allyl  iodide,  CH2  =  CH.CH2I,  is  obtained. 
This  reacts  with  silver  hydroxide,  forming  silver  iodide  and  allyl  alcohol. 
Allyl  iodide  is  employed  in  the  artificial  preparation  of  oil  of  mustard,  or  allyl 
iso-sulpho-cyanate,  and  oil  of  garlic,  or  allyl  sulphide.  These  products  are 
found  in  nature  and  are  salts  of  allyl  alcohol. 

By  oxidation  with  potassium  permanganate  allyl  alcohol  is  reconverted  into 
glycerin. 


ALCOHOLS.  487 

Allyl  alcohol  is  a  colorless  liquid  possessing  a  disagreeable  penetrating  odor. 
It  is  soluble  in  water  in  all  proportions ;  B.  P.  96.5°  C. 

Glycerin,  Glycerinum,  C3H5(OH)3  =  91.37  (Glycerol).  This  is 
a  triatomic  alcohol,  in  which  three  OH  groups  have  replaced  three 
hydrogen  atoms  in  propane,  CH3.CH2.CH3.  Synthetic  methods  have 
shown  the  glycerin  to  be  CH2OH.CHOH.CH2OH. 

Glycerin  is  a  normal  constituent  of  all  fats,  which  are  glycerin  in  which  the 
three  atoms  of  hydrogen  of  the  hydroxyl  have  been  replaced  by  radicals  of 
fat  acids.  It  is  obtained  as  a  by-product  in  the  manufacture  of  soap,  but  it  is 
also  largely  manufactured  by  passing  steam  under  120  to  150  pounds  pressure 
into  fats  contained  in  large  copper  digesters.  By  this  treatment  the  fats  are 
decomposed  into  glycerin,  which  remains  dissolved  in  the  water;  non-volatile 
fatty  acids,  floating  on  the  surface  of  the  solution ;  and  volatile  fatty  acids, 
which  escape  with  the  steam.  The  aqueous  solution  of  glycerin  is  first  con- 
centrated by  evaporation,  and  then  treated  with  superheated  steam,  with  which 
glycerin  volatilizes  and  is  condensed  in  suitably  constructed  vessels. 

Pure  glycerin  is  a  clear,  colorless,  odorless  liquid  of  a  syrupy  con- 
sistence, smooth  to  the  touch,  hygroscopic,  very  sweet,  and  neutral  in 
reaction,  soluble  in  water  and  alcohol  in  all  proportions,  but  insoluble 
in  ether,  chloroform,  benzol,  and  fixed  oils ;  its  specific  gravity  is 
1.246  at  25°  C. ;  it  cannot  be  distilled  by  itself  without  decomposition, 
but  is  volatilized  in  the  presence  of  water  or  when  steam  is  passed 
through  it. 

Glycerin  is  a  good  solvent  for  a  large  number  of  organic  and  inorganic  sub- 
stances ;  the  solutions  thereby  obtained  are  often  termed  glycerites  ;  official  are 
the  glycerites  of  starch,  carbolic  acid,  tannic  acid,  and  a  few  others. 

Boroglycerin  is  made  by  heating  a  mixture  of  boric  acid  and  gly- 
cerin, when  an  ether  of  the  composition  C3H5BO3  is  obtained.  It  is 
used  as  a  mild  antiseptic  agent. 

Analytical  reactions. 

1.  A  borax  bead  immersed  for  a  few  minutes  in  a  solution    of 
glycerin  (made  slightly  alkaline  with  potassium  hydroxide)  imparts 
a  green  color  to  a  non-luminous  flame,  owing  to  the  liberation  of 
boric  acid. 

2.  Glycerin  slightly  warmed  with  an  equal  volume  of  sulphuric 
acid  should  not  turn  dark,  but,  on  further  heating,  the  characteristic, 
irritating  odor  of  acrolein  is  noticed. 

Glycerin  trinitrate,  C3H5(NO3)3  (Nitro-glycerin,  Glonoin).  When 
glycerin  is  treated  with  nitric  acid,  or,  better,  with  a  mixture  of  con- 
centrated sulphuric  and  nitric  acids,  chemical  action  takes  place 


488  CONSIDERATION  OF  CARBON  COMPOUNDS. 

resulting  in  the  formation  of  glyceryl  mono-nitrate,  or  tri-nitrate, 
substances  belonging  to  the  group  of  compound  ethers,  the  constitu- 
tion of  which  will  be  explained  later. 

C3H5(OH)3  +  3HN03  =  C3H5(N03)3  +  3H2O. 

The  tri-nitro-glycerin  is  the  common  nitro-glyceriu,  a  pale-yellow 
oily  liquid,  which  is  nearly  insoluble  in  water,  soluble  in  alcohol, 
crystallizes  at  — 20°  C.  ( — 4°  F.)  in  long  needles,  and  explodes  very 
violently  by  concussion  ;  it  may  be  burned  in  an  open  vessel,  but 
explodes  when  heated  over  250°  C.  (482°  F.). 

Spirit  of  g-lyceryl  trinitrate,  Spiritus  g-lycerylis  nitratis  (Spirit 
of  glonoiri)  is  an  alcoholic  solution  of  nitro-glycerin,  containing  of  this 
substance  1  per  cent. 

Dynamite.  One  kilogram  of  nitro-glycerin  yields  after  explosion  713  liters 
of  gas,  measured  at  normal  temperature  and  pressure.  As  the  gas  temperature 
is  raised  by  explosion  to  about  7000°  C.  (13,000°  F.),  the  volume  is  comparatively 
larger,  and  the  explosive  power  of  nitro-glycerin  compared  with  that  of  gun- 
powder is  about  13  to  1.  Indeed,  the  explosions  of  pure  nitro-glycerin  are  so 
violent  that  it  is  generally  mixed  with  inert  substances,  such  as  clay,  sawdust, 
infusorial  (diatomaceous)  earth,  etc.  When  mixed  with  the  latter  it  forms  the 
extensively  used  dynamite,  which  is  more  useful  and  less  dangerous  to  handle 
than  pure  nitro-glycerin.  While  it  is  not  readily  exploded  by  pressure  or  jar, 
it  is  by  percussion ;  for  instance,,  by  fulminating  mercury  explosion. 

Mixtures  of  nitro-glycerin  and  gun-cotton  form  explosive  gelatine,  or  gelatine- 
dynamite. 

Glycerin-phosphoric  acid,  C3H5(OH)2O.PO(OH)2.  Compounds 
of  this  acid  are  met  with  in  blood,  flesh,  the  brain,  and  the  nerves. 
It  also  occurs  together  with  cholin,  as  a  result  of  the  splitting  up  of 
lecithin  (see  Index). 

The  absolute  acid  is  very  unstable,  decomposing  easily  into  glycerin 
and  phosphoric  acid.  The  commercial  article  is  a  20  per  cent,  aqueous 
solution.  It  is  obtained  by  dissolving  gradually  glacial  phosphoric 
acid  in  an  equal  weight  of  95  per  cent,  glycerin  with  moderate  heat,  and 
subsequently  heating  the  mixture  for  several  hours  at  110°  C.  Union 
takes  place  thus : 

C3H5(OH)3    -f    HPO3       =    C3H5(OH)2O.PO(OH)2. 

The  tenacious  mass  is  dissolved  in  water,  neutralized  with  milk  of 
lime,  and  filtered.  The  excess  of  lime  is  precipitated  by  a  current 
of  carbon  dioxide  and  filtered  off.  The  filtrate  is  concentrated  in  a 
vacuum  and  precipitated  with  alcohol  or  evaporated  to  dryness.  The 
calcium  salt  is  washed  with  alcohol  to  remove  glycerin,  dissolved  in 
water,  and  decomposed  with  a  calculated  amount  of  diluted  sulphuric 
acid.  (The  filtrate  is  evaporated  to  the  proper  concentration.) 


ALDEHYDES.    KETOXES.  489 

Glycerin-phosphoric  acid  is  a  clear  colorless  liquid  which  gradually 
turns  yellow,  and  decomposes  slowly  in  the  cold,  more  rapidly  when 
heated.  It  is  a  dibasic  acid  of  decidedly  acid  taste  and  reaction. 
The  normal  salts  are  soluble  in  water,  but  insoluble  in  alcohol,  and 
generally  have  an  alkaline  reaction.  The  usual  reagents  for  phos- 
phoric acid  do  not  affect  the  solution  of  glycerin-phosphoric  acid  in 
the  cold.  The  calcium,  potassium,  sodium,  lithium,  iron,  and  quinine 
salts  of  the  acid  have  been  introduced  into  medicine. 

Calcium  glycerin -phosphate,  C3H5(OH).2CaPO4  +  H,O,  is  a  white 
crystalline  powder,  soluble  in  20  parts  of  water,  but  less  soluble  in  hot  water. 
It  is  neutral  to  litmus,  but  the  commercial  product  is  sometimes  acid.  It  loses 
its  water  of  crystallization  at  or  above  130°  C. 

Sodium  glycerin-phosphate,  C3H5(OH)2.Na2PO4  +  H2O,  is  obtained 
by  neutralizing  glycerin-phosphoric  acid.  It  occurs  in  the  market  as  a  50  per 
cent,  solution  of  a  clear,  light  yellow  color. 

44.  ALDEHYDES.    KETONES. 

Aldehydes.  The  name  aldehyde  is  derived  from  alcohol  dehydro- 
genatum,  referring  to  its  method  of  formation,  viz.,  by  the  removal 
of  hydrogen  from  alcohols,  as,  for  instance : 

C2H6O    —    2H    =    C2H4O. 
Ethyl  alcohol.  Acetic  aldehyde. 

This  removal  of  hydrogen  may  be  accomplished  by  various  methods, 
as,  for  instance,  by  oxidation  of  alcohols,  when  one  atom  of  oxygen 
combines  with  two  atoms  of  hydrogen,  forming  water,  while  an  alde- 
hyde is  formed  at  the  same  time.  Aldehydes,  when  further  oxidized, 
are  converted  into  acids ;  aldehydes  are,  consequently,  the  interme- 
diate products  between  alcohols  and  acids,  and  are  frequently  looked 
upon  as  the  hydrides  of  the  acid  radicals.  The  constitution  of  acetic 

QUESTIONS. — What  is  the  general  constitution  of  alcohols,  and  what  is  the 
difference  between  monatomic,  diatomic,  and  triatomic  alcohols?  How  do 
alcohols  occur  in  nature  ?  By  what  processes  may  alcohols  be  formed  arti- 
ficially, and  how  may  they  be  separated  from  their  combinations  ?  State  the 
general  properties  of  alcohols.  Mention  names  and  composition  of  the  first 
five  members  of  alcohols  of  the  general  composition  CnH2n+iOH.  By  what 
process  is  methyl  alcohol  obtained,  under  what  other  names  is  it  known,  and 
what  are  its  properties?  Describe  the  manufacture  of  pure  alcohol  from 
sugar.  Give  the  alcoholic  strength  of  the  alcohol  and  diluted  alcohol  of  the 
U.  S.  P.,  and  also  of  spirit  of  wine,  proof-spirit,  light  wines,  heavy  wines,  beers, 
and  spirits.  What  are  the  general  properties  of  common  alcohol  ?  How  is 
alcohol  denatured  ?  What  is  glycerin,  how  is  it  found  in  nature,  how  is  it 
obtained,  and  what  are  its  properties  ? 


490  CONSIDERATION  OF  CARBON  COMPOUNDS. 

acid  may  be  represented  by  the  formula  CH3.CO.OH ;  the  radical  of 
acetic  acid  or  acetyl  is  the  group  CH3.CO,  and  the  hydride  of  acetyl 

/TT  /FT 

is  acetic  aldehyde,  CH3.C^Q.  It  is  the  group — C\o  which  is  char- 
acteristic of,  and  found  in,  all  aldehydes.  Only  a  few  aldehydes  are 
of  practical  interest,  as,  for  instance,  formaldehyde,  acetic  aldehyde, 
paraldehyde,  and  benzoic  aldehyde. 

xTT 

Formic  aldehyde,  CH2O  or  H.C/Q  (Formaldehyde,  methyl  alde- 
hyde). This  is  obtained  by  the  dry  distillation  of  calcium  formate, 
or  by  gentle  oxidation  of  methyl  alcohol.  The  latter  process  is 
carried  out  by  passing  vapors  of  methyl  alcohol  with  air  over  a 
heated  spiral  of  platinum  or  copper.  The  condensed  vapors  are 
formaldehyde  dissolved  in  undecomposed  methyl  alcohol.  Another 
process  is  by  heating  paraformaldehyde,  which  yields  formaldehyde 
in  a  pure  condition. 

Formaldehyde  is  a  colorless  gas,  possessing  a  strong,  penetrating 
odor;  it  may  be  condensed  to  a  liquid  which  boils  at  — 20°  C. 
(-4°  F.). 

Solution  of  formaldehyde,  Liquor  formaldehydi.  Forma-lde- 
hyde  is  readily  soluble  in  water,  and  a  solution  containing  37  per  cent, 
by  weight  is  official.  It  is  a  colorless  liquid  which  has  a  pungent 
odor  and  caustic  taste ;  its  vapors  act  as  an  irritant  upon  the  mucous 
membrane.  Sometimes  on  standing,  always  on  slow  evaporation,  white, 
solid  paraformaldehyde  separates.  With  ammonio-silver  nitrate  the 
solution  gives  a  precipitate  of  metallic  silver.  The  solution  is  a 
strong  antiseptic,  and  when  diluted  to  4  or  5  per  cent,  it  is  one  of  the 
best  hardening  and  preserving  agents  for  tissues. 

Formic  aldehyde  may  be  recognized  by  Schijf's  reaction:  A  solution  of 
fuchsin  (rosanilin  chloride)  decolorized  or  nearly  so  with  sulphurous  acid  turns 
pink  or  violet  when  brought  in  contact  with  any  aldehyde  solution.  For  the 
examination  of  air,  suspended  filter-paper,  moistened  with  the  decolorized 
fuchsin  solution,  may  be  used. 

Paraformaldehyde,  C3H6O3  or  (CH2O)3  (Formalin).  On  slow 
evaporation  of  a  solution  of  formaldehyde  in  methyl  alcohol  poly- 
merization takes  place,  and  paraformaldehyde  separates  in  colorless 
crystals  which  are  insoluble  in  water.  On  heating  the  compound, 
which  is  now  found  in  the  market  in  the  form  of  tablets,  it  splits 
up  into  three  molecules  of  formaldehyde,  which,  escaping  as  a 
gas,  is  used  for  disinfecting  purposes.  It  acts  powerfully  on  all 
germs,  and  has  the  advantage  over  chlorine  and  sulphur  dioxide  that 
it  does  not  act  injuriously  on  the  fabric  or  color  of  household  goods. 


ALDEHYDES.     KETONES.  491 

Formaldehyde  gas  is  now  very  generally  used  for  disinfecting  rooms,  etc., 
and  has  practically  displaced  the  method  of  burning  sulphur  to  obtain  sulphur 
dioxide.  The  simplest  method  of  filling  a  closed  space  with  the  gas  is  to  pour 
the  commercial  solution  of  formaldehyde  upon  small  crystals  of  potassium  per- 
manganate, contained  in  a  spacious  metallic  vessel.  A  vigorous  reaction  takes 
place,  with  destruction  of  a  portion  of  the  formaldehyde,  approximately 
according  to  this  reaction  : 

4KMn04   +   3HCOH   +   H20   =   4MnO(OH)2   +   2K2C03  +   CO2. 

The  great  heat  produced  causes  nearly  all  the  remaining  solution  to  vaporize 
and  fill  the  space  with  formaldehyde  gas  and  water  vapor,  which  latter  is  an 
essential  factor  in  the  disinfection.  The  temperature  of  the  room  should  be 
not  less  than  10°  C.  (50°  F.),  but  a  higher  temperature  is  better.  The  propor- 
tions adopted  by  some  Boards  of  Health  are  500  c.c.  of  formaldehyde  solution 
and  237  grammes  of  potassium  permanganate  per  1000  cubic  feet  of  space.  It 
is  well  known  that  formaldehyde  is  mainly  a  surface  disinfectant,  having  very 
little  power  to  penetrate  objects,  as  clothing,  etc. 

The  formaldehyde  odor  clinging  for  days  to  rooms  which  have  been  disin- 
fected by  it  may  be  quickly  removed  by  evaporation  of  some  ammonia  water, 
hexamethylene  tetramin,  (CH2)6N4,  being  formed. 


Acetic  aldehyde,  C2H4O  or  CH3.C        (Ethyl  aldehyde).     Alcohol 

may  be  converted  into  aldehyde  by  the  action  of  various  oxidizing 
agents  ;  the  one  generally  used  is  potassium  dichromate  in  the  pres- 
ence of  sulphuric  acid,  which  oxidizes  two  hydrogen  atoms  of  the 
alcohol  molecule,  converting  it  into  aldehyde  : 

C2H60    +    O    =    C2H40    +    H20. 

Experiment  56.  Place  in  a  500  c.c.  flask,  provided  with  a  funnel-tube  and 
connected  with  a  Liebig's  condenser,  6  grammes  of  potassium  dichromate. 
Pour  upon  this  salt  through  the  funnel-tube,  very  slowly,  a  previously  pre- 
pared and  cooled  mixture  of  5  c.c.  of  sulphuric  acid,  24  c.c.  of  water  and  6  c.c. 
of  alcohol.  Chemical  action  begins  generally  without  application  of  heat,  and 
often  becomes  so  violent  that  the  liquid  boils  up,  for  which  reason  a  large  flask 
is  used.  The  escaping  vapors,  which  are  a  mixture  of  aldehyde,  alcohol,  and 
water,  are  collected  in  a  receiver  kept  cold  by  ice.  From  this  mixture  pure 
aldehyde  may  be  obtained  by  repeated  distillation.  Use  the  distillate  for 
silvering  a  test-tube  by  adding  some  ammoniated  silver  nitrate.  How  much 
potassium  dichromate  is  needed  for  the  conversion  of  5  grammes  of  pure 
alcohol  into  aldehyde? 

Aldehyde  is  a  neutral,  colorless  liquid,  having  a  strong  and  charac- 
teristic odor  ;  it  mixes  with  water  and  alcohol  in  all  proportions  and 
boils  at  21°  C.  (69.8°  F.).  The  most  characteristic  chemical  property 
of  aldehyde  is  its  tendency  to  combine  directly  with  a  great  number 
of  substances;  thus  it  combines  with  hydrogen  to  form  alcohol,  with 
oxygen  to  form  acetic  acid,  with  ammonia  to  form  aldehyde-ammonia, 


492  CONSIDERATION  OF  CARBON  COMPOUNDS. 

C2H4O.NHS,  a  beautifully  crystallizing  substance,  with  hydrocyanic 
acid  to  form  aldehyde  hydrocyanide,  C2H4O.HCN,  with  acid  sulphites 
and  with  many  other  substances.  In  the  absence  of  such  other  sub- 
stance it  unites  often  with  itself,  forming  polymeric  modifications, 
such  as  paraldehyde  and  metaldehyde. 

Aldehyde  is  a  strong  reducing  agent,  which  property  is  used  in  the 
silvering  of  glass,  which  is  done  by  adding  aldehyde  to  an  ammoniacal 
solution  of  silver  nitrate,  when  metallic  silver  is  deposited  on  the  walls 
of  the  vessel  or  upon  substances  immersed  in  the  solution. 

Paraldehyde,  C6H12O3.  When  a  few  drops  of  concentrated  sul- 
phuric acid  are  added  to  aldehyde,  this  becomes  hot  and  solidifies  on 
cooling  to  0°  C.  (32°  F.).  This  solid  crystalline  mass  of  paralde- 
hyde, which  liquefies  at  10.5°  C.  (51°  F.),  has  been  formed  by  the 
direct  union  of  three  molecules  of  common  aldehyde.  Paraldehyde 
is  soluble  in  8.5  parts  of  water,  boils  at  124°  C.  (253°  F.),  and  is 
reconverted  into  common  aldehyde  by  boiling  it  with  dilute  sulphuric 
or  hydrochloric  acid.  It  is  official  as  Paraldehydum  and  a  hypnotic. 

Metaldehyde,  (C2H40)3,  is  stereo-isomeric  with  paraldehyde ;  it  is  obtained  by  a 
process  similar  to  the  one  mentioned  for  paraldehyde,  but  at  a  lower  tempera- 
ture. It  is  a  solid  crystalline  substance,  insoluble  in  water,  but  slightly  soluble 
in  alcohol,  ether,  and  chloroform. 

Trichloraldehyde,  Chloral,  C^CLjO  or  CC13.C^Q  (Trichlorace- 
tyl  hydride).  This  substance  may  be  looked  upon  as  acetic  aldehyde, 
C2H4O,  in  which  three  atoms  of  hydrogen  have  been  replaced  by 
chlorine.  It  is  made  by  passing  a  rapid  stream  of  dry  chlorine  into 
pure  alcohol  to  saturation,  keeping  the  alcohol  cool  during  the  first 
few  hours,  and  warming  it  gradually  until  the  boiling-point  is 
reached.  According  to  the  quantity  of  alcohol  operated  on,  the  con- 
version requires  several  hours  or  even  days.  The  crude  liquid  pro- 
duct separates  into  two  layers ;  the  lower  is  removed  and  shaken  with 
three  times  its  volume  of  strong  sulphuric  acid  and  distilled,  the  dis- 
tillate is  mixed  with  calcium  oxide  and  again  distilled ;  the  portion 
passing  over  between  94°  and  99°  C.  (201°  and  210°  F.)  is  collected. 

The  decomposition  taking  place  between  alcohol  and  chlorine  may 
be  explained  by  the  formation  of  aldehyde  : 

C2H6O     +    2C1    =    C2H4O     +    2HC1, 

and  by  the  subsequent  replacement  of  hydrogen  by  chlorine : 
C2H4O     +     6C1    =    C2HC130     +    3HC1 


ALDEHYDES.     KETONES.  493 

The  actual  decomposition  is,  however,  somewhat  more  complicated, 
numerous  intermediate  bodies  and  other  decomposition  products 
being  formed  at  the  same  time. 

Chloral  is  a  colorless,  oily  liquid,  having  a  penetrating  odor  and  an 
acrid,  caustic  taste;  its  specific  gravity  is  1.5,  and  its  B.  P.  95°  C. 
(202°  F.). 

Hydrated  chloral,  Chloralum  hydratum,  CC13.CH(OH)2  =164.12. 
When  water  is  added  to  chloral  the  two  substances  combine,  heat  is  dis- 
engaged, and  the  hydrate  of  chloral  is  formed,  which  is  a  crystalline, 
colorless  substance,  having  an  aromatic,  penetrating  odor,  a  bitter, 
caustic  taste,  and  a  neutral  reaction  ;  it  is  freely  soluble  in  water. 
alcohol,  and  ether,  also  soluble  in  chloroform,  carbon  disulphide, 
benzene,  fatty  and  essential  oils,  etc.  ;  it  liquefies  when  mixed  with 
carbolic  acid  or  with  camphor;  it  melts  at  58°  C.(136°  F.),and  boils 
at  95°  C.  (203°  F.),  and  also  volatilizes  slowly  at  ordinary  temperature. 

Chloral,  and  its  hydrate,  are  decomposed  by  weak  alkalies  into 
chloroform  and  a  formate  of  the  alkali  metal  : 

C2HC130    +    KHO    :       KCHO2    +    CHC13. 
Chloral.  Potassium         Potassium         Chloroform. 

hydroxide.          formate. 

This  decomposition  was  believed  to  take  place  in  the  animal  body,  and 
especially  in  the  blood,  whenever  chloral  was  given  internally,  but  recent  in- 
vestigations seem  to  contradict  this  assumption.  There  is  no  chemical  antidote 
which  may  be  used  in  cases  of  poisoning  by  chloral,  and  the  treatment  is, 
therefore,  confined  to  the  use  of  the  stomach-pump  and  to  the  maintenance  of 
respiration. 

Analytical  reactions  for  chloral. 

1.  Chloral  or  hydrated  chloral  heated  with  potassium  hydroxide  is 
converted  into  potassium  formate  and  chloroform,  which  latter  may 
be  recognized  by  its  odor.     (See  explanation  above.) 

2.  Heated  with  silver  nitrate  and  ammonium  hydroxide  a  silver- 
mirror  is  formed  on  the  glass. 

3.  Heated  with  Fehling's  solution  a  red  precipitate  is  formed. 
See  also  reactions  2  and  6  for  chloroform. 


Acrylic  aldehyde,  CH2  =  CH.C  (Acrolein),  may  be  obtained  by 
the  careful  oxidation  of  allyl  alcohol,  or  by  the  dehydrating  action 
of  potassium  acid  sulphate  on  glycerin  : 

C3H803  -  2H,0  =  C3H40. 

It  is  also  formed  by  the  destructive  distillation  of  glycerin,  which  is  a 
constituent  of  fats.     Hence,  acrolein  is  formed  when  fats  are  heated 


494  CONSIDERATION  OF  CARBON  COMPOUNDS. 

to  a  point  of  decomposition,  and  its  presence  is  noticed  by  the  pecu- 
liar penetrating  odor. 

Acrolein  is  a  highly  volatile  liquid,  boiling  at  52.4°  C.  It  has  a 
characteristic,  penetrating  odor  and  its  vapors  act  on  the  eyes,  causing 
the  secretion  of  tears.  Acrolein  shows  in  its  chemical  behavior  its 
aldehydic  nature.  It  takes  up  oxygen  forming  acrylic  acid;  com- 
bines with  hydrogen  forming  allyl  alcohol  ;  combines  directly  with 
hydrochloric  acid,  ammonia,  etc. 

Ketones  or  acetones.  These  are  compounds  containing  the 
bivalent  radical  carbonyl,  CO  <,  to  which  two  hydrocarbon  radicals 
are  attached.  The  relation  existing  between  carbonic  acid,  organic 
acids,  aldehydes,  and  ketones  is  best  shown  by  the  following  formulas, 
in  which  R  stands  for  any  hydrocarbon  radical  : 


Carbonic  acid.  Organic  acid.  Aldehyde.  Ketone. 

While  aldehydes  are  obtained  by  the  oxidation  of  primary  alcohols,  ketones 
are  the  first  product  of  the  oxidation  of  secondary  alcohols.     For  instance  : 

C2H5.CH2.OH  +  O  =  C2H5.COH  +  H2O. 

Primary  propyl  Propionic 

alcohol.  aldehyde. 


.  O  =        ,CO  +  H20. 

Secondary  propyl  Dimethyl 

alcohol.  ketone. 

Ketones  are  neutral  substances  which  resemble  aldehyde  in  so  far  as  they 
have  the  power  to  unite  directly  with  many  substances  with  which  aldehydes 
combine  ;  as,  for  instance,  with  the  acid  sulphites.  On  the  other  hand,  while 
aldehydes  readily  take  up  oxygen  directly  and  form  acids,  ketones  are  decom- 
posed by  oxidizing  agents. 

Acetone,  Acetonum,  CH3.CO.CH3  =  57.61  (Dimethyl-ketone). 
This  compound  is  obtained  by  the  destructive  distillation  of  acetates 
(and  of  a  number  of  other  substances).  The  decomposition  which 
calcium  acetate  suffers  may  be  shown  by  the  equation  : 

CH3COO\p    __  CHgXpp,    |    p_p/-i 
CH3COO/Ca  -  CH3XC(          CaC0*- 
Calcium  acetate.          Acetone. 

Acetone  is  a  colorless  liquid,  boiling  at  56.5°  C.  (133.7°  1?.),  rnis- 
eible  with  water,  alcohol,  and  ether  in  all  proportions  ;  it  has  a  pecu- 
liar ethereal,  somewhat  mint-like  odor,  and  burns  with  a  luminous 
non-sooty  flame. 


ALDEHYDES.     KETONES.  495 

Sulphur  derivatives.  A  comparison  of  such  inorganic  compounds 
as  H2S,  CS2,  NH4SH,  with  H2O,  CO2,  NH4OH,  shows  that  sulphur 
often  replaces  oxygen.  Correspondingly,  sulphur  frequently  replaces 
oxygen  in  organic  compounds.  When  this  replacement  takes  place 
in  alcohols  compounds  are  formed,  called  mercaptans,  mlpho-alcohols, 
or  thio-alcohoh;  when  it  takes  place  in  aldehydes  sulph-aldehydes  are 
formed.  These  bodies,  as  a  general  rule,  are  ill-smelling  compounds, 
some  of  which  are  the  result  of  putrefaction  in  proteids. 

When  mercaptans  are  treated  with  oxidizing  agents  three  atoms  of  oxygen 
e  taken  up  and  compounds  are  formed  which  are  called  sulphonic  acids, 

na  • 


are 
thus: 

C2H5SH    -f    30   =    C2H5.S02OH. 

Ethyl  Ethyl  sulphonic 

mercaptan.  acid. 

Sulphonic  acids  correspond  to  sulphurous  acid  in  which  a  hydrogen  atom 
has  been  replaced  by  a  hydrocarbon  radical. 

Ketones  form  condensation  products  with  both  alcohols  and  mercaptans 
thus: 

CH3\m         HO.C2H5        CH3\p/OC2H 
CH3XCO  +  HO.C2H55  " 


Acetone.  Ethyl  Ketol. 

alcohol. 


Acetone.  Ethyl  Mercaptol. 

mercaptan. 

By  oxidizing  mercaptol  with  potassium  permanganate  it  takes  up  oxygen 
(similar  to  mercaptans),  with  the  result  that  a  compound  is  formed  containing 
sulphonic  acid  : 

CH3\r/SC2H5  CH3\r/S02C2H5 

C  +  '•        =  CH3/C\S02C2H6' 


Mercaptol.  Diethylsulphon- 

dimethyl-methane. 

This  compound  is  used  medicinally  under  the  name  of  sulphonal. 

The  relations  between  methane  and  some  of  its  derivatives,  which  have  been 
considered  in  this  chapter,  may  be  shown  graphically  thus  : 


H\p/Cl  H\n/I  H\C/COH 

H/\H  C1XC\C1  I/C\I  H/°\H     • 

Methane.  Chloroform.  lodoform.  Aldehyde. 


Cl\r/COH  ^p/CH,,  CH3\r/S02C2H6 

Cl/Sd  °/C\CH3  CH3X°\S02C2H6 

Chloral.  Acetone.  Hul  phonal. 

Sulphonmethane,  Sulphonmethanum,  Sulphonal,  (CH3)2C- 
(C2H5SO2)2  =  226.55  (Diethylsulphon-dimethyl-methane).  Sulphonal 
is  a  white  crystalline  substance,  having  neither  odor  nor  taste  ;  it  is 


496  CONSIDERATION  OF  CARBON  COMPOUNDS. 

soluble  in  15  parts  of  boiling  and  360  parts  of  cold  water,  soluble 
with  difficulty  in  alcohol;  it  fuses  at  125.5°  C.  (258°  F.),  and  vola- 
tilizes at  about  300°  C.  (572°  F.),  with  partial  decomposition.  A 
mixture  of  sul  phonal  with  either  wood  charcoal  or  with  potassium 
cyanide  evolves,  on  heating,  the  characteristic  odor  of  mercaptan.  It 
is  used  as  an  hypnotic  and  soporific. 

Sulphonethylmethane,  Trional,  (?H'>C<c22H?S022    (Diethylsulphon- 


methyl-ethyl-methane),  and  Tetronal,  c'EP^C^H-o^  (Diethylsulphon- 
diethyl-methane),  are  both  colorless  solids,  forming  lustrous  crystals,  soluble  in 
hot  water  and  in  alcohol  and  ether.  The  therapeutic  action  of  these  bodies 
is  similar  to  that  of  sulphonal. 


45.    MONOBASIC  FATTY  ACIDS. 

General  constitution  of  organic  acids.  When  hydroxyl,  OH, 
replaces  hydrogen  in  hydrocarbons,  alcohols  are  formed ;  when  the 
univalent  group,  CO2H,  known  as  carboxyl,  replaces  hydrogen  in 
hydrocarbons,  acids  are  formed ;  and  all  acids  containing  this  radical 
are  termed  carboxylic  acids.  Monatomic,  diatomic,  and  triatomic 
alcohols  are  formed  by  introducing  hydroxyl  once,  twice,  or  three 
times  respectively  into  hydrocarbon  molecules;  monobasic,  dibasic, 
and  tribasic  acids  are  formed  by  substituting  one,  two,  or  three 
hydrogen  atoms  by  carboxyl.  For  instance  : 

Hydrocarbons.  Monobasic  acids.  Dibasic  acids. 

CH4  CH3C02H  CH2\C%H- 

Methane.  Acetic  acid.  Malonic  acid. 

C2H6  C2H5CO2H  ^2^*\CO2H* 

Ethane.  Propionic  acid.  Succinic  acid. 

As  stated  before,  organic  acids  may  also  be  considered  as  carbonic 

QUESTIONS. — What  is  an  aldehyde,  and  what  are  its  relations  to  alcohols 
and  acids  ?  Give  composition,  mode  of  manufacture,  and  properties  of  form- 
aldehyde. Explain  the  action  of  chlorine  upon  alcohol.  Give  the  compo- 
sition and  properties  of  chloral  and  hydrated  chloral.  What  decomposition 
takes  place  when  alkalies  act  upon  chloral  ?  Under  what  conditions  is  acro- 
lein  formed  and  what  are  its  properties  ?  Give  the  general  composition  of 
ketones  and  a  general  method  of  obtaining  them.  How  is  acetone  prepared? 
Which  compounds  are  called  mercaptans,  and  how  are  they  converted  into 
sulphonic  acids  ?  Give  method  for  preparing  sulphonal,  and  state  its  prop- 
erties. 


MONOBASIC  FATTY  ACIDS.  497 

acid  in  which  one  of  the  hydroxyl  groups  has  been  replaced  by  a 
hydrocarbon  radical,  thus: 


Carbonic  acid.  Acetic  acid.  f^ 

D\OH 
Malonic  acid. 

This  shows  that  carboxyl,  CO2H,  is  made  up  of  hydroxyl,  OH, 
and  the  bivalent  radical,  CO,  termed  carbonyl.  By  replacement  of 
the  hydrogen  of  the  hydroxyl  (or  of  the  carboxyl,  which  is  the  same) 
by  metals  the  various  salts  are  formed. 

What  is  termed  the  acid  radical  is  the  group  of  the  total  number 
of  atoms  present  in  the  molecule,  with  the  exception  of  the  hydroxyl. 
In  acetic  acid,  C2H4O2,  for  instance,  the  radical  is  CH3CO,  or  C2H3O, 
which  group  of  atoms,  known  as  acetyl,  is  characteristic  of  acetic 
acid,  and  of  all  acetates,  and  may  often  be  transferred  from  one  com- 
pound into  another  without  decomposition. 

The  difference  between  alcohol  radicals  and  acid  radicals  may  also 
be  stated,  by  saying  that  the  first  contain  carbon  and  hydrogen  only, 
while  acid  radicals  contain  carbon,  hydrogen,  and  oxygen. 

In  a  similar  manner,  as  there  are  homologous  series  of  alcohols 
corresponding  to  the  various  series  of  hydrocarbons,  there  are  also 
homologous  series  of  organic  acids  running  parallel  with  the  corre- 
sponding series  of  hydrocarbons  or  alcohols. 

Occurrence  in  nature.  Organic  acids  are  found  and  formed  both 
in  vegetables  and  animals,  and  are  present  either  in  the  free  state,  or 
(and  more  generally)  in  combination  with  bases  as  salts,  or  with 
alcohols  as  compound  ethers.  Uncombined  or  as  salts  are  found,  for 
instance,  citric,  tartaric,  and  oxalic  acids  in  plants,  formic  acid  in 
some  insects,  uric  acid  in  urine,  etc.  ;  as  compound  ethers  are  found 
many  of  the  fatty  acids  in  the  various  fats. 

Some  organic  acids  are  also  found  as  products  of  the  decomposition 
of  organic  matters  in  nature. 

Formation  of  acids.  Many  acids  are  produced  by  oxidation  of 
alcohols.  As  intermediate  products  are  formed  aldehydes,  which 
may  be  looked  upon  (as  stated  in  the  last  chapter)  as  alcohols  from 
which  two  atoms  of  hydrogen  have  been  removed. 

The  change  of  a  primary  alcohol  into  an  aldehyde,  and  of  this 
into  an  acid,  takes  place  according  to  the  general  formulas  : 

32 


498  CONSIDERATION  OF  CARBON  COMPOUNDS. 

R.CH2OH  +  O  ==  O=C^  +  H20. 
Alcohol.  Aldehyde. 

°=<H  +  O  =  °=<OH- 
Aldehyde.  Acid. 

Acids  are  obtained  from  compound  ethers  by  boiling  them  with 
alkalies,  Avhen  salts  are  formed,  which  may  be  decomposed  by  sul- 
phuric or  other  acids.  For  instance  : 

+  KOH  = 


Ethyl  acetate. 

2C2H3KO2 

Potassium 
acetate. 

Potassium 
hydroxide. 

+  H2SO4  = 

Sulphuric 
acid. 

Potassium 
acetate. 

=  2C2H4O2  - 
Acetic  acid. 

Ethyl  alcohol. 

f  K2S04. 

Potassium 
sulphate. 

Acids  are  formed  also  by  destructive  distillation  (acetic  acid)  ;  by 
fermentation  (lactic  acid)  ;  by  putrefaction  (butyric  acid)  ;  by  oxida- 
tion of  many  organic  substances  (oxalic  acid  by  oxidation  of 
starch),  etc. 

Properties.  Organic  acids  show  the  characteristics  mentioned  of 
inorganic  acids,  viz.,  when  soluble,  have  an  acid  or  sour  taste,  redden 
litmus,  and  contain  hydrogen  replaceable  by  metals,  with  the  forma- 
tion of  salts. 

Most  organic  acids,  and  especially  the  higher  members,  show  these 
acid  properties  in  a  less  marked  degree  than  inorganic  acids  ;  in  fact, 
they  become  so  weak  that  the  acid  properties  can  often  scarcely  be 
recognized.  As  stated  above,  mono-,  di-,  and  tri-basic  organic  acids 
are  known,  the  latter  two  being  capable  of  forming  normal,,  acid,  or 
double  salts. 

Most  organic  acids  are  colorless,  some  of  the  lower  and  volatile 
acids  have  a  characteristic  odor,  but  most  of  them  are  odorless  ;  most 
organic  acids  are  solids,  some  liquids,  scarcely  any  gaseous  at  the  ordi- 
nary temperature.  Any  salt  formed  by  the  union  of  an  organic  acid 
and  a  non-volatile  metal  (especially  alkali  metal)  leaves  the  carbonate 
of  this  metal  after  the  salt  has  suffered  combustion.  It  is  for  this 
reason  that  ashes  contain  metals  largely  in  the  form  of  carbonates. 

While  the  hydrogen  of  the  hydroxyl  may  be  replaced  by  metals 
or  by  other  residues,  the  hydrogen  of  the  acid  radical  may  often  be 
replaced  by  chlorine,  and  the  oxygen  of  the  hydroxyl  by  sulphur. 
The  acids  formed  by  this  last  reaction  are  known  as  thio  acids,  for 
instance,  thio-acetic  acid,  C2H4OS. 

When  the  hydrogen  of  the  hydroxyl  is  replaced  by  a  second  acid 


MONOBASIC  FATTY  ACIDS, 


499 


radical  (of  the  same  kind  as  the  one  forming  the  acid)  the  so-called 
anhydrides  are  produced,  which  correspond  to  the  inorganic  anhy- 
drides. For  instance : 


Nitric  acid. 

N02\o 
N02/° 

Nitric  anhydride. 


C2H4O2  or  C2H3O.OH. 
Acetic  acid. 

C2H30\0 
C2H30/a 

Acetic  andydride. 


It  is  evident  from  the  above  that,  while  acids  are  hydroxides  of 
acid  radicals,  the  anhydrides  are  oxides.  They  are  often  formed  by 
abstracting  water  from  two  molecules  of  an  acid,  thus : 

C2H3O.Oin     _  C2H30\0    ,    H0 
C2H3O.OH/  -  C2H30/°  +  H2°' 

Amino-acids  are  compounds  obtained  from  acids  by  replacement  of 
a  hydrogen  atom  of  the  acid  radical  by  NH2 ;  these  compounds  will 
be  spoken  of  later  in  connection  with  amides. 

Patty  acids  of  the  general  composition, 
CnH2n02  or  CnH2n  +  1C02H. 

Occurs  in : 


Fusing-    Boiling- 
point,       point. 


Formic  acid, 

H  CO2H 

-f  4°C. 

100' 

Acetic  acid, 

C  H3C02H 

+17 

118 

Propionic  acid, 

C2  H5  C02H 

—21 

140 

Butyric  acid, 

C3  H7  CO2H 

—20 

162 

Valeric  acid, 

C4  H9  CO2H 

—16 

185 

Caproic  acid, 

C5  HUC02H 

—  2 

205 

(Enanthylic  acid, 

C6  H13C02H 

—10 

224 

Caprylic  acid, 

C7  H15C02H 

+14 

236 

Pelargonic  acid, 

C8  H17C02H 

18 

254 

Capric  acid, 

C9  H19C02H 

30 

270 

Laurie  acid, 

CUH23C02H 

43 



Myristic  acid, 

C13H27C02H 

54 



Palmitic  acid, 

C15H31CO2H 

62 



Margaric  acid, 

CieHssCOjjH 

60 



Otearic  acid, 

C17H35C02H 

70 



Arachidic  acid, 

/""I     TT      f~^r\   TT 
L^igilggVAyg  "• 

75 



Behenic  acid, 

C21H43CO2H 

76 



Hysenic  acid, 

C24H49C02H 

77 

Cerotic  acid, 

C26H53C02H 

80 



Melissic  acid, 

C^     TT      C*f}  TT 

90 



Vegetable  and  animal  fluids. 

Sweat,  fluids  of  the  stomach,  etc. 

Butter. 

Valerian  root. 

Butter. 

Castor  oil. 

Butter ;  cocoanut  oil. 

Leaves  of  geranium. 

Butter. 

Cocoanut  oil. 

Palm  oil,  butter. 
(Obtained  artificially.) 
Most  solid  animal  fats. 

Oils  of  certain  plants. 
Beeswax. 


The  name  fatty  acids  has  been  given  to  these  acids  on  account  of 
their  frequent  occurrence  in  fats,  and  also  in  allusion  to  the  some- 
what fatty  appearance  of  the  higher  members  of  the  series. 

The  gradual  change  of  properties  which  the  members  of  an  homol- 
ogous series  show,  is  well  marked  in  the  series  of  fatty  acids,  thus  : 


500  CONSIDERATION  OF  CARBON  COMPOUNDS. 

First  member.  Last  member. 

Is  liquid.  Is  solid. 

Volatilized  at  100°  C.  Not  volatilized  without  decomposition. 

Strongly  acid .  Scarcely  acid. 

Strongly  odoriferous.  Odorless. 

Easily  soluble  in  water.  Insoluble  in  water. 

Produces  no  grease  spot.  Produces  a  grease  spot. 
Forms  salts  easily  soluble  without         Forms  salts  which  are  insoluble  or  de- 
decomposition,  composed  by  water. 

The  intermediate  members  of  the  series  show  intermediate  proper- 
ties, and  this  change  in  properties  is  in  proportion  to  the  gradual 
change  in  molecular  weight. 

Formic  acid,  H.CO2H  or  CHO.OH.  This  acid  is  found  in  the 
red  ant  and  in  other  insects,  which  eject  it  when  irritated.  It  is  also 
contained  in  some  plants,  as,  for  instance,  in  the  leaves  of  the  sting- 
ing-nettle. 

It  is  formed  by  the  oxidation  of  methyl  alcohol : 

CH40    4-    02    =    CH.202    4-    H2O, 
Methyl  alcohol.  Formic  acid. 

by  the  action  of  carbonic  oxide  on  potassium  hydroxide: 

KOH    4-    CO    ;       KCHO2, 

Potassium  formate. 

by  the  action  of  potassium  hydroxide  on  chloroform  : 
CHCla  4-  4KOH  =  3KC1  4-  2H2O  4  KCHO2, 

by  the  action  of  potassium  on  moist  carbon  dioxide : 
2CO2  4-  ttjO  4-  2K  =  KHCO3  +  KCHO2, 

by  heating  equal  parts  of  glycerin  and  oxalic  acid,  when  the  latter  is 
split  up  into  carbon  dioxide  and  formic  acid,  which  may  be  separated 
from  the  glycerin  by  distillation  : 

C2H2O4    =    CO2    4-    CH2O2. 
Oxalic  acid.  Formic  acid. 

It  is  also  a  product  of  the  decomposition  of  sugar,  starch,  etc. 
Formic  acid  is  a  colorless  liquid  having  a  penetrating  odor,  and  a 
strongly  acid  taste ;  it  produces  blisters  on  the  skin  ;  it  is  a  powerful 
deoxidizer,  being,  when  thus  acting,  converted  into  carbon  dioxide 

and  water : 

CH2O2    +    O    =    C02    4-    H20. 

Acetic  acid,  H.C2H3O2,  or  C2H3O.OH,  or  CH3.CO2H  =  59.58. 
The  most  important  alcohol  is  ethyl  alcohol,  and  the  most  largely 
used  organic  acid  is  acetic  acid,  obtained  from  ethyl  alcohol  by  oxi- 


MONOBASIC  FATTY  ACIDS.  501 

dation.  Acetic  acid  is  found  in  combination  with  alkali  metals  in 
the  juices  of  many  plants,  also  in  the  secretions  of  some  glands,  etc. 

There  are  many  reactions  by  which  acetic  acid  can  be  obtained 
similar  to  formic  acid.  For  all  practical  purposes,  however,  it  is 
made  either  by  the  oxidation  of  alcohol  (and  aldehyde)  or  by  the 
destructive  distillation  of  wood.  It  is  produced  commercially  on  a 
large  scale  as  follows  :  A  diluted  alcohol  (8  to  10  per  cent.)  is  allowed 
to  trickle  down  slowly  through  wood  shavings  contained  in  high 
casks  having  perforated  sides  in  order  to  allow  a  free  circulation  of 
the  air ;  the  temperature  is  kept  at  about  24°  to  30°  C.  (75°  to  86° 
F.),  and  the  liquid  having  passed  through  the  shavings  is  repeatedly 
poured  back  in  order  to  cause  complete  oxidation.  When  the  latter 
object  has  been  accomplished  the  liquid  is  a  diluted  acetic  acid. 

It  appears  that  the  conversion  of  alcohol  into  acetic  acid  is  greatly 
facilitated  by  the  presence  of  a  microscopic  organism  (mycoderma 
aceti)  commonly  termed  "  mother  of  vinegar."  This  serves  in  some 
unexplained  way  to  convey  the  atmospheric  oxygen  to  the  alcohol. 
The  term  "  acetic  fermentation  "  is  often  applied  to  this  conversion, 
although  it  is  not  a  true  fermentation,  since  no  splitting  up  of  the 
alcohol  molecule  into  other  less  complex  compounds,  but  a  process  of 
slow  oxidation,  takes  place. 

The  second  process  for  manufacturing  acetic  acid  is  the  heating  of 
wood  to  a  red  heat  in  iron  retorts,  when  numerous  products  (gases, 
aqueous  and  tarry  substances)  are  formed.  The  aqueous  products 
contain,  besides  other  substances,  methyl  alcohol  and  acetic  acid. 
The  liquid  is  neutralized  with  calcium  hydroxide  and  distilled,  when 
methyl  alcohol,  water,  etc.,  evaporate  and  a  solid  residue  is  left,  which 
is  an  impure  calcium  acetate.  From  this  latter,  acetic  acid  is  obtained 
by  distilling  with  sulphuric  (or  hydrochloric)  acid,  calcium  sulphate 
(or  chloride)  being  formed  and  left  in  the  retort,  while  acetic  acid 
distils  over. 

Experiment  57.  Add  to  54  grammes  of  sodium  acetate  contained  in  a  small 
flask  which  is  connected  with  a  Liebig's  condenser,  40  grammes  of  sulphuric 
acid.  Apply  heat  and  distil  over  about  35  c.c. '  Determine  volumetrically  the 
amount  of  pure  acetic  acid  in  this  liquid. 

Pure  acetic  acid,  or  glacial  acetic  acid,  is  solid  at  or  below  15°  C. 
(59°  F.);  at  higher  temperatures  it  is  a  colorless  liquid  having  a 
characteristic,  penetrating  odor,  boiling  at  118°  C.  (244.4°  F.),  and 
causing  blisters  on  the  skin ;  its  specific  gravity  is  1.049  at  25°  C. ; 
it  is  miscible  with  water,  alcohol,  and  ether,  is  strongly  acid,  forming 
salts  known  as  acetates,  which  are  all  soluble  in  water. 


502  CONSIDERATION  OF  CARBON  COMPOUNDS. 

Vinegar  is  dilute  acetic  acid  (about  6  per  cent.),  containing  often 
other  substances,  such  as  coloring  matter,  compound  ethers,  etc. 
Vinegar  was  formerly  obtained  exclusively  by  the  oxidation  of  fer- 
mented fruit-juices  (wine,  cider,  etc.),  the  various  substances  present 
in  them  imparting  a  pleasant  taste  and  odor  to  the  vinegar ;  to-day 
vinegar  is  often  made  artificially  by  adding  various  coloring  and 
odoriferous  substances  to  dilute  acetic  acid.  Vinegar  should  be  tested 
for  sulphuric  and  hydrochloric  acids,  which  are  sometimes  fraudu- 
lently added. 

Acidum  aceticum,  Acidum  aceticum  dilutum,  and  Acidum  aceticum 
glaciale  are  the  three  official  forms  of  acetic  acid.  The  first-named 
acid  contains  36  per  cent.,  the  second  6  per  cent.,  the  third  at  least  99 
per  cent,  of  pure  acetic  acid. 

Acetic  acid  shows  an  exceptional  behavior  in  regard  to  the  specific 
gravity  of  its  aqueous  solutions.  The  highest  specific  gravity  of 
1.0748  belongs  to  an  acid  of  78  per  cent.,  which  is  equal  to  an  acid 
containing  one  molecule  of  water  and  one  of  acetic  acid,  or  C2H4O2.H2O. 
When  the  acid  and  water  are  mixed  in  this  proportion,  a  maximum 
rise  in  temperature  and  contraction  in  volume  take  place,  which  fact 
indicates  the  existence  of  ortho-acetic  acid,  CH3C(OH)3,  some  ethereal 
salts  of  which  are  known.  The  addition  of  either  acetic  acid  or  of 
water  causes  the  liquid  to  become  lighter.  For  instance,  the  specific 
gravity  of  an  acid  containing  95  per  cent,  is  equal  to  that  containing 
56  per  cent,  of  pure  acid,  both  solutions  having  a  specific  gravity  of 
1.066. 

The  specific  gravity  of  dilute  acetic  acid  cannot,  therefore,  be 
used  as  a  means  of  determining  the  amount  of  pure  acid ;  this  is 
done  by  exactly  neutralizing  a  weighed  portion  of  the  acid  with 
an  alkali ;  from  the  quantity  of  the  latter  used,  the  quantity  of 
actual  acid  present  may  be  easily  calculated.  (See  also  volumetric 
methods  in  Chapter  39.) 

The  vapor  density  of  absolute  acetic  acid  at  just  a  little  above  its  boiling- 
point  is  twice  as  great  as  that  corresponding  to  the  formula,  C2H4O2.  At 
200°  C.  or  above,  the  vapor  density  is  normal.  This  kind  of  behavior  has 
been  observed  in  the  case  of  other  substances. 

While  vinegar  is  used  in  our  diet,  it  should  be  remembered  that  acetic  acid 
acts  as  an  irritant  and  corrosive,  having  caused  in  some  instances  perforation 
of  the  stomach,  and  death  in  6  to  15  hours.  Milk  of  magnesia  should  be  given 
as  an  antidote  with  a  view  of  neutralizing  the  acid. 


MONOBASIC  FATTY  ACIDS.  503 

Analytical  reactions. 
(Sodium  acetate,  NaC2H3O2,  may  be  used.) 

1.  Any  acetate   heated  with  sulphuric  acid   evolves  acetic  acid, 
which  may  be  recognized  by  its  odor. 

2.  Acetic  acid  or  acetates  heated  with  sulphuric  acid  and  alcohol 
give  a  characteristic  odor  of  acetic  ether. 

3.  A  solution  containing  acetic  acid,  or  an  acetate  carefully  neutral- 
ized, turns  deep  red  on  the  addition  of  solution  of  ferric  chloride, 
and  forms,  on  boiling,  a  reddish-brown  precipitate  of  an  oxyacetate 
of  iroa 

Potassium  acetate,  Potassii  acetas,  KC2H3O2  =  97.44.  Sodium 
acetate,  Sodii  acetas,  NaC2H3O2.3H2O  ===  135.1.  Zinc  acetate, 
Zinci  acetas,  Zn  (C2H3O2)2.2H2O  =  217.82.  These  three  salts  may 
be  obtained  by  neutralizing  the  respective  carbonates  with  acetic  acid 
and  evaporating  the  solution ;  they  are  white  salts,  easily  soluble  in 
water. 

Ammonium  acetate,  NH4C2H3O2,  is  official  in  the  form  of  a  7 
per  cent,  solution,  which  is  known  as  Spirit  of  Mindererus. 

Iron  acetates.  Both  the  ferrous  acetate,  Fe(C2H3O2)2.4H20,  and  the  ferric 
acetate,  Fe(C2H3O2)3,  are  known.  The  latter  is  formed  by  adding  sodium  ace- 
tate to  the  solution  of  a  ferric  salt,  as  is  indicated  by  the  deep-red  color  which 
the  solution  assumes.  As  stated  above  in  reaction  3,  on  boiling,  decomposition 
of  the  salt  takes  place.  The  separation  of  manganese  and  some  other  metals 
from  iron  depends  on  this  reaction. 

Lead  acetate,  Plumbi  acetas,  Pb(C2H3O2)23H2O  =  376.15  (Sugar 
of  lead),  is  made  by  dissolving  lead  oxide  in  diluted  acetic  acid.  It 
forms  colorless,  shining,  transparent  crystals,  easily  soluble  in  water; 
on  heating,  it  melts  and  then  loses  water  of  crystallization ;  at  yet 
higher  temperatures  it  is  decomposed ;  it  has  a  sweetish,  astringent, 
afterward  metallic  taste.  Commercial  sugar  of  lead  contains  often  an 
excess  of  lead  oxide  in  the  form  of  basic  salts ;  such  an  article  when 
dissolved  in  spring  water  gives  generally  a  turbid  solution,  in  conse- 
quence of  the  formation  of  lead  carbonate ;  the  addition  of  a  few 
drops  of  acetic  acid  renders  the  liquid  clear  by  dissolving  the  pre- 
cipitate. 

When  a  mixture  of  lead  acetate  and  lead  oxide  is  digested  or  boiled 
frith  water,  the  acetate  combines  with  the  oxide,  forming  a  basic  lead 


504  CONSIDERATION  OF  CARBON  COMPOUNDS. 

acetate,  approximately  Pb(C2H3O2)2.PbO,  a  25  per  cent,  solution  of 
which  is  the  Liquor  plumbi  subacetatis,  or  Goulard's  extract,  while  a 
solution  containing  about  1  per  cent,  is  the  Liquor  plumbi  subacetatis 
dilutus,  or  lead-water.  Other  more  basic  compounds  are  known.  So- 
called  tribasic  lead  acetate  has  the  formula  Pb(C2H3O2)2.2PbO. 

Cupric  acetate,  Cu(C2H3O2)2H2O.  The  commercial  verdigris  is  a 
basic  acetate  of  copper,  Cu(C2H3O2)2CuO7  made  by  the  action  of 
dilute  acetic  acid  and  atmospheric  air  on  metallic  copper.  By  adding 
to  this  basic  acetate  more  acetic  acid,  the  neutral  acetate  is  obtained, 
but  this  may  be  made  directly  also  by  dissolving  cupric  hydroxide 
or  carbonate  in  acetic  acid.  It  forms  deep  green,  prismatic  crystals, 
which  are  soluble  in  water. 

By  boiling  verdigris  with  arsenous  oxide,  cupric  aceto-arsenite, 
3CuAs2O4  -f-  Cu(C2H3O2)2,  is  formed,  which  is  the  chief  constituent 
of  emerald  green  or  Schweinfurt  green,  a  substance  often  used  as  a 
coloring  matter.  Paris  green  is  of  a  similar  composition,  but  less 
pure. 

Chlorine  substitution  products  of  acetic  acid.  The  action  of  chlor- 
ine gas  and  of  phosphorus  trichloride  on  acetic  acid  furnishes  an  additional 
proof  of  the  correctness  of  our  views  regarding  its  constitution  and,  conse- 
quently, of  the  constitution  of  organic  acids  in  general.  It  has  been  shown 
that  chlorine  in  acting  on  a  hydrocarbon  (methane)  will  successively  replace  all 
hydrogen  present.  Similarly  we  can,  by  treatment  with  chlorine,  replace  that 
hydrogen  in  acetic  acid  which  is  derived  from  the  hydrocarbon,  with  the  result 
that  monochlor,  dichlor,  and  trichlor  acetic  acids  are  formed  : 

CH3.COOH  +  2C1  :  :  CH2C1.COOH  +  HC1, 
CH2C1.COOH  +  2C1  =  CHC12.COOH  +  HC1, 
CHC12.COOH  +  2C1  CC13.COOH  -f  HC1. 

The  fourth  atom  of  hydrogen  cannot  be  directly  replaced  by  chlorine.  As  it  is 
this  carboxyl  hydrogen  atom  to  which  the  acid  properties  are  due  the  above 
three  compounds  have  acid  properties. 

The  action  of  phosphorus  trichloride  on  water,  on  methyl  alcohol,  and  on 
acetic  acid  takes  place  thus  : 

3**>0    +    PC13    «    3HC1  +    P(OH)3, 


+    PC13    =    3CH3C1        +    P(OH)3, 
3C2H30>0    +     pcla    =    3C2H3OC1     +     P(OH)3. 

In  all  three  cases  the  hydro*xyl  group  is  replaced  by  chlorine,  with  the  result 
that  hydrogen  chloride  (hydrochloric  acid),  methyl  chloride,  and  acetyl  chloride 
are  formed. 


MONOBASIC  FATTY  ACIDS.  505 

'Trichlor-acetic  acid,  Acidum  trichloraceticum,  CC13.CO2H 
162.12.  As  shown  in  the  previous  paragraph,  this  acid  may  be  ob- 
tained by  the  direct  action  of  chlorine  on  acetic  acid,  but  it  is  usually 
made  by  the  oxidation  with  nitric  acid  of  chloral  (tricolor-aldehyde), 
which  requires  but  one  atom  of  oxygen  for  its  conversion  into  tri- 
chlor-acetic  acid. 

Trichlor-acetic  acid  is  a  white,  deliquescent,  crystalline  substance. 
It  has  a  slight,  characteristic  odor,  is  readily  soluble  in  water,  alcohol, 
and  ether.  The  aqueous  solution,  on  boiling,  is  decomposed  into 
chloroform  and  carbon  dioxide.  It  is  used  as  a  local  caustic  and  as 
a  reagent  for  albumin. 

Acetyl  chloride,  CH3.COC1,  is  obtained  by  distilling  a  mixture  of  9  parts 
of  glacial  acetic  acid  and  6  parts  of  phosphorus  trichloride  on  a  water-bath  at 
a  slightly  elevated  temperature.  It  is  a  colorless  liquid,  having  a  suffocating 
odor,  boiling-point  of  55°  C.,  and  specific  gravity  1.13  at  0°  C.  It  fumes  in 
the  air,  and  acts  on  water  energetically,  thus : 

CH3COC1  +  H2O  =  CH3COOH  +  HC1. 

It  is  a  valuable  reagent  for  testing  for  alcoholic  hydroxyl  groups  in  organic 
compounds,  which  may  be  illustrated  by  its  action  on  ordinary  alcohol,  thus: 

CH3COC1  +  C2H5OH  =  CH3COOC2H5  +  HC1. 

Acetates  are  thus  formed  by  the  replacement  of  hydrogen  of  hydroxyl  by  the 
acetyl  radical. 

Acetic  anhydride  or  acetyl  oxide,  (CH3CO)20,  is  formed  by  distilling  a 
mixture  of  anhydrous  sodium  acetate  and  acetyl  chloride  : 

CH3COONa  +  CH3COC1  =  (CH3CO)2O  +  NaCl. 

It  is  a  colorless  liquid  with  a  disagreeable  odor,  boiling  at  137°  C.,  and  having 
a  specific  gravity  of  1.073  at  20°  C.  It  is  soluble  in  about  10  parts  of  water, 
the  solution  decomposing  slowly  with  formation  of  acetic  acid.  Like  acetyl 
chloride,  it  unites  with  hydroxyl  groups  in  organic  compounds,  forming  ace- 
tates. This  process  of  making  acetates  from  alcoholic  compounds  is  called 
acetylization,  and  is  often  used  in  analysis  of  substances. 

Butyric  acid,  HC4H702.  Among  the  glycerides  of  butter  those  of  butyric 
acid  are  found ;  they  exist  also  in  cod-liver  oil,  croton  oil,  and  a  few  other  fatty 
oils ;  some  volatile  oils  contain  compound  ethers  of  butyric  acid ;  free  butyric 
acid  occurs  in  sweat  and  in  cheese.  It  may  be  obtained  by  a  peculiar  fermen- 
tation of  lactic  acid  (which  itself  is  a  product  of  fermentation),  and  is  also 
generated  during  the  putrefaction  of  albuminous  substances.  Butyric  acid  is 
a  colorless  liquid,  having  a  characteristic,  unpleasant  odor;  it  mixes  with 
water  in  all  proportions. 

Valeric  acid,  HC5H9O2  (Valerianic  avid).  This  acid  occurs  in 
valerian  root  and  angelica  root,  from  which  it  may  be  separated ;  it 


506  CONSIDERATION  OF  CARBON  COMPOUNDS. 

is,  however,  generally  obtained  by  oxidation  of  amyl  alcohol  by 
potassium  dichromate  and  sulphuric  acid.  After  oxidation  has  taken 
place  the  mixture  is  distilled,  when  valeric  acid  with  some  valerate 
of  amyl  distils  over.  The  change  of  amyl  alcohol  into  valeric  acid  is 
analogous  to  the  conversion  of  ethyl  alcohol  into  acetic  acid  : 

C5HnOH    +     2O    =    HC5H902     +    H2O. 
Amyl  alcohol.  Valeric  acid. 

Pure  valeric  acid  is  an  oily,  colorless  liquid,  having  a  penetrating, 
highly  characteristic  odor ;  it  is  slightly  soluble  in  water,  but  soluble 
in  alcohol ;  it  boils  at  185°  C.  (365°  F.). 

Ammonium  valerate  and  zinc  valerate  are  official.  Both  are  white  solids  hav- 
ing the  odor  of  valeric  acid.  The  ammonium  salt  is  readily,  the  zinc  salt  spar- 
ingly soluble  in  water. 

Stearic  acid,  Acidum  stearicum,  HC^H^C^  =  282.14.  The 
official  stearic  acid  is  the  commercial,  more  or  less  impure  article 
made  from  solid  fats,  chiefly  tallow.  It  is  a  hard,  white,  somewhat 
glossy  solid  without  odor  or  taste.  It  is  insoluble  in  water,  but  solu- 
ble in  alcohol,  ether  and  alkalies.  Both  stearic  acid  and  palmitic 
acid,  HC16H31O2,  occur  largely  in  solid  fats.  The  general  properties 
of  palmitic  acid  are  nearly  identical  with  those  of  stearic  acid.  (See 
analytical  reactions  of  fats.) 

Oleic  acid,  Acidum  oleicum,  HC18H33O2  =  280.14.  As  shown  by 
its  formula,  oleic  acid  does  not  belong  to  the  above-described  series  of 
fatty  acids  of  the  composition  CnH2nO2,  but  to  a  series  having  the 
general  composition  CnH2n-2O2. 

These  acids  belong  to  the  ethylene  series — i.  e.,  they  contain  two 
carbon  atoms  held  together  by  a  double  bond,  in  virtue  of  which 
they  are  oxidized  more  readily  than  the  corresponding  saturated 
acids.  They  also  form  addition  products ;  oleic  acid,  for  instance, 
combines  directly  with  2  atoms  of  hydrogen,  forming  stearic  acid, 
and  with  bromine  to  form  dibrom-stearic  acid. 

Oleic  acid  is  a  constituent  of  most  fats,  especially  of  fat  oils. 
Thus,  olive  oil  is  mainly  oleate  of  glyceryl.  By  boiling  olive  oil  with 
potassium  hydroxide,  potassium  oleate  is  formed,  which  may  be 
decomposed  by  tartaric  acid,  when  oleic  acid  is  liberated. 

Oleic  acid  is  a  nearly  colorless,  yellowish,  or  brownish-yellow, 
neutral  oily  liquid,  having  a  peculiar,  lard-like  odor  and  taste.  It  is 
insoluble  in  water,  soluble  in  alcohol,  chloroform,  oil  of  turpentine, 
and  fat  oils,  crystallizing  near  the  freezing-point  of  water ;  exposed 


MONOBASIC  FATTY  ACIDS.  507 

to  the  air  it  decomposes  and  shows  then  an  acid  reaction.  Lead 
oleate  is  soluble  in  ether,  lead  palmitate  and  lead  stearate  are 
not. 

The  official  oleates  of  mercury,  quinine,  veratrine,  atropine,  and 
cocaine  are  obtained  by  dissolving  the  yellow  mercuric  oxide,  quinine, 
veratrine,  atropine,  or  cocaine  in  oleic  acid. 

Dissociation  of  formic  acid  and  its  homologues.  In  Chapter  15  it  is 
stated  that  the  "  strength  "  or  relative  activity  of  acids  and'bases  is  propor- 
tional to  their  degree  of  dissociation  in  solution.  Organic  acids  in  solution  are 
dissociated  only  to  a  small  degree  and  are  much  "  weaker  "  than  such  mineral 
acids  as  hydrochloric,  nitric,  and  sulphuric,  which  are  almost  completely  disso- 
ciated in  very  dilute  solutions.  The  following  table  shows  the  percentage  of 
molecules  dissociated  in  aqueous  solutions  containing  the  molecular  weight  in 
grams  of  the  respective  acids  diluted  to  8  liters : 


Formic  acid. 

Acetic  acid. 

Propionic  acid. 

Normal  butyric  acid. 

4.05 

1.193 

1.016 

1.068 

Further  dilution  does  not  increase  the  percentage  of  dissociation  very  much. 
For  example,  the  molecular  weight  of  acetic  acid  in  16  liters  of  solution  disso- 
ciates only  to  the  extent  of  1.673  per  cent.,  whereas  in  a  similar  solution  of 
hydrochloric  acid  the  dissociation  is  95.5  per  cent.  Formic  acid  dissociates 
more  than  the  others  of  the  series,  and  is,  therefore,  the  strongest  acid  of  the 
series.  The  salts  of  organic  acids  are  dissociated  much  more  than  the  acids 
are.  Thus,  in  a  normal  solution  of  acetic  acid  only  0.4  per  cent,  of  the  molecules 
are  dissociated,  while  in  normal  solutions  of  sodium  and  potassium  acetate 
53  per  cent,  and  64  per  cent,  respectively,  of  the  molecules  are  dissociated. 

QUESTIONS. — What  is  the  constitution  of  organic  acids,  what  group  of 
atoms  is  found  in  all  of  them,  and  how  does  an  alcohol  radical  differ  from  an 
acid  radical?  Give  some  processes  by  which  organic  acids  are  formed  in  nature 
or  artificially.  Mention  the  general  properties  of  organic  acids.  Which  series 
of  acids  is  known  as  fatty  acids,  and  why  has  this  name  been  given  to  them  ? 
Mention  names,  composition,  and  occurrence  in  nature  of  the  first  five  mem- 
bers of  the  series  of  fatty  acids.  By  what  processes  may  formic  acid  be  ob- 
tained, and  what  are  its  properties?  Describe  the  processes  of  manufacturing 
acetic  acid  from  alcohol  and  from  wood.  What  is  vinegar,  and  what  is  glacial 
acetic  acid  ?  Give  tests  for  acetic  acid  and  for  acetates.  Describe  the  pro- 
cesses for  making  the  acetates  of  potassium,  zinc,  iron,  lead,  and  copper,  and 
also  of  Goulard's  extract  and  lead-water ;  state  their  composition  and  proper- 
ties. Where  and  in  what  form  of  combination  is  oleic  acid  found  in  nature, 
and  what  are  its  properties  ? 


510  CONSIDERATION  OF  CARBON  COMPOUNDS. 

tion.     This  fact  indicates  that  the  iron  is  held  in  a  complex  ion, 

since  the   color  of  simple   ferrous   salts   in   solution   is   usually  pale  green. 

The    salt    has    strong  reducing   properties   and   is   used   as   a   developer   in 

photography. 

Potassium  ferric  oxalate,  K3Fe(C2O4)3,  gives  a  green  solution,  and  the  iron  is 
^robably  held  in  a  complex  ion,  Fe(C2O4)3///.  It  is  rapidly  reduced  by  sun- 
light, thus, 

2K3Fe(CA)3    =    2K2Fe(C204)2     +     K2C2O4    +     2CO2, 
and,  therefore,  is  useful  in  making  platinotypes  in  photography. 

Hydroxy-acids. 

In  the  acids  heretofore  considered,  the  hydrogen  is  derived  either 
from  the  hydrocarbon  radical  or  from  carboxyl.  There  are,  however, 
compounds  containing  as  a  third  radical  hydroxyl  —  i.  e.,  that  radical 
characteristic  of  alcohols.  Consequently  Ave  may  look  upon  these 
compounds  as  acids  into  which  alcoholic  hydroxyl  has  been  intro- 
duced, or  as  alcohols  into  which  carboxyl  has  been  introduced.  The 
acid  properties  of  these  compounds  are  so  predominating  that  the 
compounds  are  spoken  of  as  acids,  and  according  to  the  number  of 
carboxyl  groups  present  we  have  monobasic,  dibasic,  etc.,  acids.  The 
hydrogen  of  the  carboxyl  is,  of  course,  replaceable  by  metals,  while 
the  hydrogen  of  the  alcoholic  hydroxyl  can  be  replaced  by  hydrocar- 
bon radicals.  In  order  to  indicate  this  diiference  in  the  function  of 
the  hydrogen  the  number  of  the  respective  groups  present  is  given  in 
the  name.  Thus,  tartaric  acid,  which  contains  2  hydroxyl  and  2  car- 
boxyl groups,  is  designated  as  a  dibasic  hydroxy-acid,  or  as  dihy- 
droxy-dicarboxylic  acid,  while  citric  acid,  which  contains  1  hydroxyl 
and  3  carboxyl  groups,  is  a  monohydroxy-tribasic  acid  or  hydroxy- 
tricarboxylic  acid. 

Of  the  several  methods  known  for  obtaining  hydroxy-acids  only  one  shall  be 
mentioned.  It  corresponds  to  one  of  the  methods  used  for  the  introduction  of 
hydroxyl  into  hydrocarbons  ;  in  one  case  the  halogen  of  a  hydrocarbon,  in  the 
other  case  the  halogen  of  an  acid  is  replaced  by  hydroxyl  : 

CH3Br     +     H20    :  CH3OH     +     HBr, 


Brom-acetic  acid.  Hydroxy-acetic  acid. 

It  is  evident  from  what  has  been  said  that  we  have  running  parallel  to  every 
series  of  acids  another  series  of  hydroxy-acids.     For  instance  thus  : 


POLYBASIC  AND  HYDROXY-ACIDS.  511 

Fatty  acids.  Hydroxy-acids. 

Formic  acid,  ILCO2H.  Hydroxy-formic  acid,  OH.CO2H. 

Acetic  acid,  CH3.CO2.H.  Hydroxy-acetic  acid,  CH2.OH.CO2H. 

Propionic  acid,  C2H6.CO2H.  Hydroxy-propionic  acid,  C2H4.OH.CO;,H. 

etc.  etc. 

The  first  member  of  these  hydroxy-acids  designated  as  hydroxy-formic  acid 

is  simply  carbonic  acid  and  does  not  partake  of  the  general  character  of 
hydroxy-acids. 

Monohydroxy-monobasic  acids. 

Gly colic  acid,  CH2.OH.CO2H  (Hydroxy-acetic  acid),  is  found  in 
unripe  grapes  and  in  the  leaves  of  the  wild  grape.  It  can  be  obtained 
synthetically,  as  shown  in  the  previous  paragraph.  It  may  also  be 
made  by  the  oxidation  of  ethylene  alcohol  or  ylycol,  C2H4(OH)2  thus : 

C2H4(OH)2    -f    20    =    CH2.OH.C02H    +    H2O. 

Glycolic  acid  is  a  white  deliquescent,  crystalline  substance,  easily 
soluble  in  water,  alcohol,  and  ether. 

Lactic  acid,  Acidum  lacticum,  C2H4.OH.CO2H  —  89.37  (Hy- 
droxy-propionic acid),  occurs  in  many  plant-juices;  it  is  formed  from 
sugar  by  a  peculiar  fermentation  known  as  "lactic  fermentation," 
which  causes  the  presence  of  this  acid  in  sour  milk  and  in  many  sour, 
fermented  substances,  as  in  ensilage,  sauer-kraut,  etc.  The  formation 
of  lactic  acid  from  sugar  may  be  expressed  by  the  equation  : 

C6H1206    =    2(HC3H503). 

Sugar.  Lactic  acid. 

For  practical  purposes  lactic  acid  is  made  by  mixing  a  solution  of 
sugar  with  milk,  putrid  cheese,  and  chalk,  and  digesting  this  mixture 
for  several  weeks  at  a  temperature  of  about  30°  C.  (86°  F.).  The 
bacteria  in  the  cheese  act  as  a  ferment,  and  the  chalk  neutralizes  the 
acid  generated  during  the  fermentation.  The  calcium  lactate  thus 
obtained  is  purified  by  crystallization  and  decomposed  by  oxalic  acid, 
which  forms  insoluble  calcium  oxalate. 

Lactic  acid  is  a  colorless,  syrupy  liquid,  of  strongly  acid  properties ; 
it  mixes  in  all  proportions  with  water  and  alcohol.  The  official 
lactic  acid  contains  75  per  cent,  of  absolute  acid. 

Three  isomeric  lactic  acids  are  known : 

a.  Fermentation  lactic  acid,  obtained  as  described  above  from  milk,  is  opti- 
cally inactive. 

b.  Sarcolactic  or  paralactic  acid  is  dextrorotatory  and  occurs  in  muscle  and 
other  parts  of  the  body.     It  forms  a  constituent  of  meat-juice,  and,  therefore, 
of  meat  extract. 

c.  Lcevolactic  acid  is  laevorotatory,  and  is  obtained  from  cane  sugar  by  fer- 
mentation by  a  special  micro-organism. 


510  CONSIDERATION  OF  CARBON  COMPOUNDS. 

tion.  This  fact  indicates  that  the  iron  is  held  in  a  complex  ion,  Fe(C2O4)2//, 
since  the  color  of  simple  ferrous  salts  in  solution  is  usually  pale  green. 
The  salt  has  strong  reducing  properties  and  is  used  as  a  developer  in 
photography. 

Potassium  ferric  oxalate,  K3Fe(C2O4)3,  gives  a  green  solution,  and  the  iron  is 
,»robably  held  in  a  complex  ion,  Fe(C2O4)3///.  It  is  rapidly  reduced  by  sun- 
light, thus, 

2K3Fe(CA)3    =    2K2Fe(C204)2     +     K2C2O4    +     2CO2, 
and,  therefore,  is  useful  in  making  platinotypes  in  photography. 

Hydroxy-acids. 

In  the  acids  heretofore  considered,  the  hydrogen  is  derived  either 
from  the  hydrocarbon  radical  or  from  carboxyl.  There  are,  however, 
compounds  containing  as  a  third  radical  hydroxyl  —  i.  e.,  that  radical 
characteristic  of  alcohols.  Consequently  we  may  look  upon  these 
compounds  as  acids  into  which  alcoholic  hydroxyl  has  been  intro- 
duced, or  as  alcohols  into  which  carboxyl  has  been  introduced.  The 
acid  properties  of  these  compounds  are  so  predominating  that  the 
compounds  are  spoken  of  as  acids,  and  according  to  the  number  of 
carboxyl  groups  present  we  have  monobasic,  dibasic,  etc.,  acids.  The 
hydrogen  of  the  carboxyl  is,  of  course,  replaceable  by  metals,  while 
the  hydrogen  of  the  alcoholic  hydroxyl  can  be  replaced  by  hydrocar- 
bon radicals.  In  order  to  indicate  this  difference  in  the  function  of 
the  hydrogen  the  number  of  the  respective  groups  present  is  given  in 
the  name.  Thus,  tartaric  acid,  which  contains  2  hydroxyl  and  2  car- 
boxyl groups,  is  designated  as  a  dibasic  hydroxy-acid,  or  as  dihy- 
droxy-dicarboxylic  acid,  while  citric  acid,  which  contains  1  hydroxyl 
and  3  carboxyl  groups,  is  a  monohydroxy-tribasic  acid  or  hydroxy- 
tricarboxylic  acid. 

Of  the  several  methods  known  for  obtaining  hydroxy-acids  only  one  shall  be 
mentioned.  It  corresponds  to  one  of  the  methods  used  for  the  introduction  of 
hydroxyl  into  hydrocarbons  ;  in  one  case  the  halogen  of  a  hydrocarbon,  in  the 
other  case  the  halogen  of  an  acid  is  replaced  by  hydroxyl  : 

CH3Br    +     H20    :  CH3OH    +     HBr, 


Brom-acetic  acid.  Hydroxy-acetic  acid. 

It  is  evident  from  what  has  been  said  that  we  have  running  parallel  to  every 
series  of  acids  another  series  of  hydroxy-acids.     For  instance  thus  : 


POLYBASIC  AND  HYDROXY-ACIDS.  511 

Fatty  acids.  Hydroxy-acids. 

Formic  acid,  H.CO2H.  Hydroxy-formic  acid,  OH.CO2H. 

Acetic  acid,  CH3.CO2.H.  Hydroxy-acetic  acid,  CH2.OH.CO2H. 

Propionic  acid,  C2PI6.CO2H.  Hydroxy-propionic  acid,  C2H4.OH.CO.,H. 

etc.  etc. 

The  first  member  of  these  hydroxy-acids  designated  as  hydroxy-formic  acid 
is  simply  carbonic  acid  and  does  not  partake  of  the  general  character  of 
hydroxy-acids. 

Monohydroxy-monobasic  acids. 

Gly colic  acid,  CH2.OH.CO2H  (Hydroxy-acetic  acid),  is  found  in 
unripe  grapes  and  in  the  leaves  of  the  wild  grape.  It  can  be  obtained 
synthetically,  as  shown  in  the  previous  paragraph.  It  may  also  be 
made  by  the  oxidation  of  ethylene  alcohol  or  ylycol,  C2H4(OH)2  thus : 

C2H4(OH)2    -f    2O    =    CH2.OH.CO2H    +    H2O. 

Glycolic  acid   is  a  white  deliquescent,  crystalline  substance,  easily 
soluble  in  water,  alcohol,  and  ether. 

Lactic  acid,  Acidum  lacticum,  C2H4.OH.CO2H  =  89.37  (Hy- 
droxy-propionic acid),  occurs  in  many  plant-juices;  it  is  formed  from 
sugar  by  a  peculiar  fermentation  known  as  "  lactic  fermentation," 
which  causes  the  presence  of  this  acid  in  sour  milk  and  in  many  sour, 
fermented  substances,  as  in  ensilage,  sauer-kraut,  etc.  The  formation 
of  lactic  acid  from  sugar  may  be  expressed  by  the  equation  : 

C6H1206    =    2(HC3H503). 

Sugar.  Lactic  acid. 

For  practical  purposes  lactic  acid  is  made  by  mixing  a  solution  of 
sugar  with  milk,  putrid  cheese,  and  chalk,  and  digesting  this  mixture 
for  several  weeks  at  a  temperature  of  about  30°  C.  (86°  F.).  The 
bacteria  in  the  cheese  act  as  a  ferment,  and  the  chalk  neutralizes  the 
acid  generated  during  the  fermentation.  The  calcium  lactate  thus 
obtained  is  purified  by  crystallization  and  decomposed  by  oxalic  acid, 
which  forms  insoluble  calcium  oxalate. 

Lactic  acid  is  a  colorless,  syrupy  liquid,  of  strongly  acid  properties ; 
it  mixes  in  all  proportions  with  water  and  alcohol.  The  official 
lactic  acid  contains  75  per  cent,  of  absolute  acid. 

Three  isomeric  lactic  acids  are  known  : 

a.  Fermentation  lactic  acid,  obtained  as  described  above  from  milk,  is  opti- 
cally inactive. 

b.  Sarcolactic  or  paralactic  acid  is  dextrorotatory  and  occurs  in  muscle  and 
other  parts  of  the  body.     It  forms  a  constituent  of  meat-juice,  and,  therefore, 
of  meat  extract. 

c.  Lcevolactic  acid  is  laevorotatory,  and  is  obtained  from  cane  sugar  by  fer- 
mentation by  a  special  micro-organism. 


512  CONSIDERATION  OF  CARBON  COMPOUNDS. 

Dibasic  and  tribasic  hydroxy-acids. 

Mono-hydroxy-succinic  acid,  or  malic  acid  = 

/OH  CH.OH.COJH 

C4H605  or    C2H3^C02H  or     j 

XCO2H  CH2.CO2H 

Di-hydroxy-succinic  acid,  or  tartaric  acid  = 

/OH 

//OH  CH.OH.CO2H 

C4H6O6  or  C2H2  or     | 

\>C02H  CH.OH.C02H 

\CO2H 

Malic  acid,  H2C4H4O5,  occurs  in  the  juices  of  many  fruits,  as 
apples,  currants,  cherries,  etc.  It  may  be  extracted  from  these  fruits 
or  prepared  synthetically. 

Tartaric  acid,  Acidum  tartaricum,  H2C4H4O6  — - 148.92.  Fre- 
quently found  in  vegetables,  and  especially  in  fruits,  sometimes  free, 
generally  as  the  potassium  or  calcium  salt ;  grapes  contain  it  chiefly 
as  potassium  acid  tartrate,  which  is  obtained  in  an  impure  state  as  a 
by-product  in  the  manufacture  of  wine.  During  the  fermentation  of 
grape-juice,  its  sugar  is  converted  into  alcohol ;  potassium  acid  tar- 
trate is  less  soluble  in  alcoholic  fluids  than  in  water,  and  therefore  is 
deposited  gradually,  forming  the  crude  tartar,  or  argol,  of  commerce, 
a  substance  containing  chiefly  potassium  acid  tartrate,  but  also  cal- 
cium tartrate,  some  coloring  matter,  and  traces  of  other  substances. 
Crude  tartar  is  the  source  of  tartaric  acid  and  its  salts. 

Tartaric  acid  is  obtained  from  potassium  acid  tartrate  by  neutral- 
izing with  calcium  carbonate,  and  decomposing  the  remaining  neutral 
potassium  tartrate  by  calcium  chloride  : 

2(KHC4H4O6)  +  CaCO3  ==  CaC4H4O6  +  K2C4H4O6  +  H2O  +  CO2. 
Potassium  acid          Calcium  Calcium  Potassium         Water.       Carbon 

tartrate.  carbonate.         tartrate.  tartrate.  dioxide. 

K2C4H406  +  CaCl2  =  CaC4H406  +  2KC1. 
Potassium        Calcium  Calcium         Potassium 

tartrate.         chloride.  tartrate.          chloride. 

The  whole  of  the  tartaric  acid  is  thus  converted  into  calcium  tar- 
trate, which  is  precipitated  as  an  insoluble  powder ;  this  is  collected, 
well  washed,  and  decomposed  by  boiling  with  sulphuric  acid,  when 
calcium  sulphate  is  formed  as  an  almost  insoluble  residue,  while  tar- 
taric acid  is  left  in  solution,  from  which  it  is  obtained  by  evaporation 
and  crystallization  : 

CaC4H4O6  +  H2SO4  =  H,C4H4O6  -f  CaSO4. 

Calcium          Sulphuric          Tartaric  Calcium 

tartrate.  acid.  acid.  sulphate. 


POLYBASIC  AND  HYDROXY-ACIDS. 


513 


Tartaric  acid  crystallizes  in  colorless,  translucent  prisms ;  it  has  a 
strongly  acid,  but  not  disagreeable  taste ;  it  is  readily  soluble  in  water 
and  alcohol,  and  fuses  at  135°  C.  (275°  F.). 


FIG  71. 


Isomerism  of  tartaric  acid.  Four  tartaric  acids  are  known.  They  are : 
dextrotartaric  or  common  tartaric  acid;  favot ar tar ic  acid  ;  mesotartaric  or  inact- 
ive tartaric  acid;  and  racemic  add.  These  four  acids  have  the  same  composi- 
tion and  show  the  same  chemical  reactions,  proving  that  they  are  built  up  from 
the  same  radicals ;  but  in  some  respects  they  possess  different  physical  proper- 
ties. Thus,  mesotartaric  and  racemic  acids  are  optically  inactive ;  the  others, 
as  indicated  by  their  names,  are  active,  one  turning  polarized  light  to  the  right, 
the  other  to  the  left. 

Pasteur  first  observed  that  the  spontaneous  evaporation  of  a  solution  of 
ammonium  sodium  racemate  yields  two 
kinds  of  stereo-isomeric  crystals.  These 
crystals  (Fig.  71)  are  rectangular  prisms  P, 
M,  T,  having  the  lateral  edges  replaced  by 
the  faces  b' ,  and  the  intersection  of  these 
faces  with  the  face  T  replaced  by  a  face  h. 
The  crystals  are  hemihedral,  having  four  of 
these  h  faces  placed  alternately.  In  the  two 
kinds  of  crystals  these  hemihedral  faces  oc- 
cupy opposite  positions,  so  that  if  one  kind 
of  crystal  be  placed  before  a  mirror  its  re- 
flection will  represent  the  arrangement  of 
the  hemihedral  faces  of  the  other  kind  of  crystal.  The  crystals  are  called 
right-handed  and  left-handed  respectively. 

From  these  two  kinds  of  crystals  two  tartaric  acids  can  be  separated  ;  one  is 
dextrotartaric  acid,  the  other  laevotartaric  acid.  When  the  two  acids  are  brought 
together  in  solution  they  unite  forming  racemic  acid.  These  observations,  sup- 
ported by  chemical  data,  have  led  to  assume  in  tartaric  acids  the  existence  of 
two  asymmetric  carbon  atoms,  about  which  the  hydrogen  atoms  and  the  radi- 
cals are  arranged  differently.  Three  of  these  forms  may  be  represented  by  the 
formulas : 


Isomeric  salts  of  tartaric  acid. 


C02H 

H— C— OH 
OH— C— II 

C02H 

Dextrotartaric  acid. 


CO2H 
OH— C— H 


H 


-OH 


II- 


-C-OH 

C02H 
Laevotartaric  acid. 


H— O-OH 

! 
CO,H 

Mesotartaric  acid 


Racemic  acid  results  from  the  combination  of  dextrotartaric  and  laevotartaric 
acids. 

In  a  tenth-normal  solution  of  tartaric  acid  at  25°  C.,  8.2  per  cent,  of  the  acid 
is  dissociated  into  Hg  and  H.C^O/  ions. 
33 


514  CONSIDERATION  OF  CARBON  COMPOUNDS. 

Analytical    reactions. 
(Potassium  sodium  tartrate,  KNaC4H4O6,  may  be  used.) 

1.  A  neutral  solution   of  a  tartrate  gives  with  calcium  chloride  a 
white  precipitate  of  calcium  tartrate,  which,  after  being  quickly  col- 
lected on  a  filter  and  washed,  is  soluble  in  potassium  hydroxide ;  from 
this  solution  calcium  tartrate  is  precipitated  on  boiling.     (Calcium 
citrate  is  insoluble  in  potassium  hydroxide.) 

Calcium  tartrate  is  soluble  in  a  solution  of  an  alkali  tartrate; 
hence,  unless  a  sufficient  amount  of  calcium  chloride  is  added,  a  pre- 
cipitate will  not  be  obtained. 

2.  A  strong  solution  of  a  tartrate,  acidulated  with  acetic  acid,  gives 
a  white  precipitate  of  potassium  acid  tartrate  on  the  addition  of  potas- 
sium acetate.    The  precipitate,  which  forms  slowly,  is  soluble  in  alka- 
lies and  in  mineral  acids. 

In  the  case  of  potassium  sodium  tartrate,  or  potassium  tartrate, 
addition  of  acetic  acid  alone  precipitates  potassium  acid  tartrate. 

3.  A  neutral  solution  of  a  tartrate  gives  with  silver  nitrate  a  white 
precipitate  of  silver  tartrate,  Ag2C4H4O6,  which  blackens  on  boiling, 
in  consequence  of  the  decomposition  of  the  salt,  with  separation  of 
silver.      If,  before  boiling,  a  drop  of  ammonia  water  be  added,  a 
mirror  of  metallic  silver  will  form  upon  the  glass. 

Silver  tartrate  is  soluble  in  a  solution  of  alkali  tartrate  ;  hence  the 
silver  nitrate  solution  must  be  added  in  sufficient  quantity  to  obtain 
a  permanent  precipitate. 

4.  Sulphuric  acid  heated  with  tartrates  chars  them  readily. 

5.  Tartrates,  when  heated,  are  decomposed  (blacken),  and  evolve  a 
somewhat  characteristic  odor,  resembling  that  of  burnt  sugar. 

The  above  reaction,  3,  can  be  used  to  advantage  for  silvering  glass  by  operat- 
ing as  follows :  Dissolve  1  gramme  of  silver  nitrate  in  20  c.c.  of  water,  add 
ammonia  water  until  the  precipitate  which  forms  is  nearly  redissolved,  and 
dilute  with  water  to  100  c.c.  Make  a  second  solution  by  dissolving  0.2  gramme 
of  silver  nitrate  in  100  c.c.  of  boiling  water,  add  0.166  gramme  of  potassium 
sodium  tartrate,  boil  until  the  precipitate  becomes  gray,  and  filter.  Mix  the 
two  solutions  cold  and  set  aside  for  one  hour,  when  a  mirror  of  metallic  silver 
will  be  found. 

Potassium  acid  tartrate,  Potassii  bitartras.  KHC^O,,  =  186.78 
(Potassium  bitartrate,  Cream  of  Tartar).  The  formation  of  this  salt  in 


POLYBASIC  AND   HYDROXY-ACIDS.  515 

the  crude  state  (argol)  has  been  explained  above.  It  is  purified  by 
dissolving  in  hot  water  and  crystallizing,  when  it  is  obtained  in  color- 
less crystals,  or  as  a  white,  somewhat  gritty  powder  of  a  pleasant, 
acidulous  taste  ;  it  is  soluble  in  about  200  parts  of  cold,  easily  sol- 
uble in  hot  water,  but  insoluble  in  alcohol. 

The  name  cream  of  tartar  was  given  to  the  salt  for  the  reason  that 
small  crystals,  which  float  on  the  liquid,  separate  on  rapidly  cooling 
a  hot  solution  of  potassium  bitartrate. 


Potassium  tartrate,  2(K2C4H406).H,0.  Obtained  by  saturating  a  solution 
of  potassium  acid  tartrate  with  potassium  carbonate : 

2KHC4H4Oe  +  K2C03  =  2K2C4H4O6  +  H2O  +  CO,. 
Potassium  acid       Potassium        Potassium 
tartrate.  carbonate.          tartrate. 

Small  transparent  or  white  crystals,  or  a  white  neutral  powder,  soluble  in 
less  than  its  own  weight  of  water. 

Potassium  sodium  tartrate,  Potassii  et  sodii  tartras, 
KNaC4H4O6.4H2O  =  280.18  (Rochelle  salt).  If  in  the  above-described 
process  for  making  neutral  potassium  tartrate,  sodium  carbonate  is 
substituted  for  potassium  carbonate,  the  double  tartrate  of  potassium 
and  sodium  is  formed.  It  is  a  white  powder,  or  occurs  in  colorless, 
transparent  crystals  which  are  easily  soluble  in  water. 

Experiment  59.  Add  gradually  24  grammes  of  potassium  acid  tartrate  to  a 
hot  solution  of  20  grammes  of  crystallized  sodium  carbonate  in  100  c.c.  of 
water.  Heat  until  complete  solution  has  taken  place,  filter,  evaporate  to  about 
one-half  the  volume,  and  set  aside  for  the  potassium  sodium  tartrate  to  crys- 
tallize. How  much  crystallized  sodium  carbonate  is  required  for  the  conversion 
of  25  grammes  of  potassium  acid  tartrate  into  Eochelle  salt? 

Seidlitz  powders  (Compound  effervescing  powders)  consist  of  a  mixture 
of  7.75  grammes  (120  grains)  of  Rochelle  salt  with  2.58  grammes 
(40  grains)  of  sodium  bicarbonate  (wrapped  in  blue  paper),  and  2.25 
grammes  (35  grains)  of  tartaric  acid  (wrapped  in  white  paper). 
When  dissolved  in  water  the  tartaric  acid  acts  upon  the  sodium 
bicarbonate,  causing  the  formation  of  sodium  tartrate,  while  the 
escaping  carbon  dioxide  causes  effervescence. 

Antimony  and  potassium  tartrate,  Antimonii  et  potassii 
tartras,  2(KSbO.C4H4O6).H,O=659.8  (Potassium  antimonyl  tartrate, 
Tartar  emetic).  This  salt  is  made  by  dissolving  freshly  prepared 
antimonous  oxide  (while  yet  moist)  in  a  solution  of  potassium  acid 


516  CONSIDERATION  OF  CARBON  COMPOUNDS. 

tartrate.     From  the   solution   somewhat   evaporated,    tartar   emetic 
separates  in  colorless,  transparent  rhombic  crystals : 

2KHC4H4O6     +     Sb2O3    =   =    2KSbO.C4H4O6    +     H,O. 

Potassinm  acid        Antimonous  Tartar  emetic, 

tartrate.  oxide. 

The  fact  that  not  antimony  itself,  but  the  group  SbO,  replaces  the 
hydrogen,  has  led  to  the  assumption  of  the  hypothetical  radical  SbO, 
termed  antimonyl. 

Tartar  emetic  is  soluble  in  water,  insoluble  in  alcohol ;  it  has  a 
sweet,  afterward  disagreeable  metallic  taste. 

Action  of  certain  organic  acids  upon  certain  metallic  oxides.  The  solu- 
tion of  a  ferric  salt  (or  certain  other  metallic  salts)  is  precipitated  by  alkali 
hydroxides,  a  salt  of  the  alkali  and  ferric  hydroxide  being  formed.  When  a 
sufficient  quantity  of  either  tartaric,  citric,  oxalic,  or  various  other  organic 
acids  has  been  added  previously  to  the  iron  solution  (or  to  certain  other  metallic 
solutions)  no  such  precipitate  is  produced  by  the  alkali  hydroxides,  because 
organic  salts  or  double  salts  are  formed  which  are  soluble,  and  from  which  the 
metallic  hydroxides  are  not  precipitated  by  alkali  hydroxides.  Upon  evapora- 
tion no  crystals  (of  the  organic  salt)  form,  and  in  order  to  obtain  the  com- 
pounds in  a  dry  state,  the  liquid,  after  being  evaporated  to  the  consistence  of 
a  syrup,  is  spread  on  glass  plates  which  are  exposed  to  a  temperature  not 
exceeding  60°  C.  (140°  F.),  when  brown,  green,  yellowish-green,  amorphous, 
shining,  transparent  scales  are  formed,  which  are  the  scale  compounds  of  the 
U.  S.  P. 

Instead  of  obtaining  these  compounds,  'as  stated  above,  by  adding  the 
organic  acids  (or  their  salts)  to  the  inorganic  salts,  they  are  more  generally 
obtained  by  dissolving  the  freshly  precipitated  metallic  hydroxide  in  the 
organic  acid. 

The  true  chemical  constitution  of  many  of  these  scale  compounds  has  not 
as  yet  been  determined  with  certainty. 

Of  official  scale  compounds  containing  tartaric  acid  may  be  mentioned  the 
iron  and  ammonium  tartrate,  and  the  iron  and  potassium  tartrate.  The  first  com- 
pound is  obtained  by  dissolving  freshly  precipitated  ferric  hydroxide  in  a  solu- 
tion of  ammonium  acid  tartrate ;  the  second,  by  dissolving  ferric  hydroxide  in 
potassium  acid  tartrate.  The  clear  solutions,  after  having  been  sufficiently 
evaporated,  are  dried,  as  mentioned  above,  on  glass  plates. 

Citric  acid,  Acidum  citricum,  H3C6H5O7.H2O  =  2O8.5.  Citric 
acid  is  a  tribasic  acid  containing  three  atoms  of  hydrogen  replaceable 
by  metals ;  its  constitution  may  be  expressed  by  the  graphic  formulas  : 

/OH  CH2.C02H 

/>C02H  | 

C3H4  or     COH.CO2H 

\\C02H  | 

\C02H  CH2.C02H 

Citric  acid  is  found  in  the  juices  of  many  fruits  (strawberry,  rasp- 
berry, currant,  cherry,  etc.),  and  in  other  parts  of  plants.  It  is 
obtained  from  the  juice  of  lemons  by  saturating  it  with  calcium  car- 


POLYBASIC  AND  HYDEOXY- ACIDS.  517 

bonate  and  decomposing  by  sulphuric  acid  the  calcium  citrate  thus 
formed.  (100  parts  of  lemons  yield  about  5  parts  of  the  acid.)  It 
forms  colorless  crystals,  easily  soluble  in  water. 

Analytical  reactions. 
(Potassium  citrate,  K3C6H5O7,  may  be  used.) 

1.  Neutral  solutions  of  citrates  yield  with  calcium  chloride  on 
boiling  (not  in  the  cold)  a  white  precipitate  of  calcium  citrate,  which 
is  insoluble  in  potassium  hydroxide,  but  soluble  in  cupric  chloride. 

2.  Neutral  solutions  of  citrates  are  precipitated  white  by  silver 
nitrate.     The  precipitate  does  not  blacken  on  boiling,  as  in  the  case 
of  tartrates.       Silver  citrate  is  soluble  in  a  solution  of  an  alkali  ci- 
trate ;  hence,  sufficient  silver  nitrate  solution  must  be  added  to  obtain 
a  permanent  precipitate. 

3.  A  solution  of  citrate  made  alkaline  with  a  little  sodium  hydrox- 
ide solution,  to  which  a  few  drops  of  potassium  permanganate  solu- 
tion are  added,  turns  green  slowly,  whereas,  atartrate  under  the  same 
conditions  decolorizes  permanganate  quickly,   with  precipitation  of 
brown  manganese  dioxide. 

4.  When  ignited,  it  is  decomposed  without  emitting  an  odor  resem- 
bling burning  sugar.     (Difference  from  tartaric  acid.) 

5.  Tartaric  acid  in  citric  acid  may  be  detected  by  adding  about  1 
c.c.   of   an   aqueous  solution  of  ammonium   molybdate  to  about  1 
gramme   of  the   citric   acid,  then  2  or  3  drops  of  sulphuric  acid, 
and  warming  on  the  water-bath.      The  presence  of  0.1  per  cent,  or 
more  of  tartaric  acid  gives  a  blue  color  to  the  solution. 

Citrates.  Potassium  citrate,  K3C6H5O7.H2O,  and  Lithium  citrate, 
Li3C6H5O7.4H2O,  are  official.  Both  are  white  deliquescent  salts,  easily 
soluble  in  water,  and  obtained  by  dissolving  the  carbonates  in  citric 
acid.  Sodium  citrate,  2Na3C6H5O7.llH2O,  is  also  official. 

The  effervescent  potassium  citrate,  lithium  citrate,  and  magnesium  sulphate  are 
granulated  mixtures,  all  containing  citric  acid,  tartaric  acid,  and  sodium  bicar- 
bonate, mixed  respectively  with  potassium  citrate,  lithium  citrate,  and  mag- 
nesium sulphate. 

The  official  solution  of  magnesium  citrate  is  made  by  dissolving  magnesium 
carbonate  in  an  excess  of  citric  acid  solution  to  which  some  syrup  is  added, 
and  dropping  into  this  mixture,  which  should  be  contained  in  a  strong  bottle, 
potassium  bicarbonate.  The  bottle  is  immediately  closed  with  a  cork  in  order 
to  retain  the  liberated  carbon  dioxide. 

Bismuth  citrate,  BiC6H5O7,  is  obtained  by  boiling  a  solution  of  citric  acid 
with  bismuth  nitrate,  when  the  latter  is  gradually  converted  into  citrate,  while 


518  CONSIDERATION  OF  CARBON  COMPOUNDS. 

nitric  acid  is  set  free;  the  insoluble  bismuth  citrate  is  collected,  washed,  and 
dried;  it  forms  a  white,  amorphous  powder,  which  is  insoluble  in  water,  but 
soluble  in  ammonia  water. 

Bismuth  ammonium  citrate  is  a  scale  compound  obtained  by  dissolving  bismuth 
citrate  in  ammonia  water  and  evaporating  the  solution  at  a  low  temperature. 

Ferric  citrate,  Ferri  citras.  Obtained  in  transparent,  red  scales,  by  dissolving 
ferric  hydroxide  in  citric  acid  and  evaporating  the  solution  as  mentioned  here- 
tofore. By  mixing  solution  of  ferric  citrate  with  either  ammonia  water  or 
quinine,  strychnine,  sodium  phosphate,  or  sodium  pyrophosphate,  evaporating 
to  the  consistence  of  syrup  and  drying  on  glass  plates,  the  following  scale  com- 
pounds are  obtained  respectively :  Iron  and  ammonium  citrate,  iron  and  quinine 
citrate,  iron  and  strychnine  citrate,  soluble  ferric  phosphate,  and  soluble  ferric  pyro- 
phosphate. 

47.  ETHERS  AND   ESTERS. 

Constitution.  It  has  been  shown  that  alcohols  are  hydrocarbon 
residues  in  combination  with  hydroxyl,  OH,  and  that  acids  are  hydro- 
carbon residues  in  combination  with  carboxyl,  CO.OH  ;  it  has  further 
been  shown  that  carboxyl  may  be  considered  as  being  composed  of 
CO,  and  hydroxyl,  OH,  and  that  the  term  acid  radical  is  applied  to 
that  group  of  atoms  in  acids  which  embraces  the  hydrocarbon  residue 
-f-  CO.  If  we  represent  a  hydrocarbon  radical  by  R,  and  an  acid 
radical  by  R.CO,  the  general  formula  of  an  alcohol  is  R.OH,  or 

^>O,  and  of  an  acid,  R.CO.OH,  or  R'C°>O. 

Ethers  are  formed  by  replacement  of  the  hydrogen  of  the  hydroxyl 
in  alcohols  by  hydrocarbon  residues,  and  esters,  also  called  compound 
ethers,  or  ethereal  salts  are  formed  by  replacement  of  the  hydrogen  of 
the  hydroxyl  (or  carboxyl)  in  acids  by  hydrocarbon  residues.  While 
alcohols  correspond  in  their  constitution  to  hydroxides,  ethers  corre- 
spond to  oxides,  and  esters  to  salts.  For  instance : 

QUESTIONS. — Name  the  more  common  organic  acids  found  in  vegetables 
and  especially  in  sour  fruits.  What  is  the  composition  of  oxalic  acid,  how  is 
it  manufactured,  and  what  are  its  properties?  Explain  the  formation  of  crude 
tartar  during  the  fermentation  of  grape-juice,  and  how  is  tartaric  acid  obtained 
from  it?  Give  properties  of  and  tests  for  tartaric  acid.  State  the  composition 
and  formation  of  cream  of  tartar,  Rochelle  salt,  and  tartar  emetic.  What  are 
Seidlitz  powders,  and  what  changes  take  place  when  they  are  dissolved  ?  Give 
the  general  composition  of  hydroxy-acids,  and  state  a  method  for  preparing 
them  synthetically.  From  what  and  by  what  process  is  citric  acid  obtained  ? 
Mention  tests  by  which  citric  acid  may  be  distinguished  from  tartaric  acid. 
From  what  and  by  what  process  is  lactic  acid  obtained ;  what  are  its  prop- 
erties ? 


ETHERS  AND   ESTERS.  519 


Hydroxides.  Oxides.  Acids. 

KOH  =  g\0      K20  =  £\0    HN03  =  N^)0    KNO3  -  N(j£>O 
Potassium  hydroxide.    Potassium  oxide.  Nitric  acid.  Potassium  nitrate. 


Ethyl  alcohol.  Ethyl  ether.  Acetic  acid.  Ethyl  acetate,  or 

acetic  ether. 


ET  R  H  R* 

Alcohol.  Ether.  Acid.  Ester. 

It  is  not  necessary  that  the  two  hydrocarbon  residues  in  au  ether 
should  be  alike,  as  in  the  above  ethyl  ether,  but  they  may  be  different, 
in  which  case  the  ethers  are  termed  mixed  ethers.  For  instance  : 

CH3.C2H50  =  g  H»\o         q,H,AHu.O  = 

Methyl-ethyl  ether.  Propyl-amyl  ether. 

In  diatomic  or  triatomic  alcohols,  or  in  dibasic  or  tribasic  acids, 
containing  more  than  one  atom  of  hydrogen  derived  from  hydroxyl 
or  carboxyl,  these  hydrogen  atoms  may  be  replaced  by  various  other 
univalent,  bivalent,  or  trivalent  residues.  This  fact  shows  that  the 
number  of  ethers  or  esters  which  are  capable  of  being  formed  is  very 
large. 

Formation  of  ethers.  Ethers  may  be  formed  by  the  action  of 
the  chloride  or  iodide  of  a  hydrocarbon  residue  upon  an  alcohol,  in 
which  the  hydroxyl  hydrogen  has  been  replaced  by  a  metal.  For 
instance  : 

C£<>     +     QftI    =    %!;>     +    Nal. 
Sodium  ethylate.    Ethyl  iodide.       Ethyl  ether.    Sodium  iodide. 


Sodium  Methyl          Ethyl-methyl         Sodium 

ethylate.  iodide.  ether.  iodide. 

Ethers  are  also  formed  by  the  action  of  sulphuric  acid  upon  alco- 
hols ;  the  sulphuric  acid  removing  water  in  this  case,  thus  : 

2(C2H5OH)       :      2H5°    + 


Ethyl  alcohol.          Ethyl  ether.  Water. 


Esters  are  formed  by  the  combination  of  acids  with  alcohols  and 
elimination  of  water.  (Presence  of  sulphuric  acid  facilitates  this 
action.) 


+     C2HS0\0     = 

Ethyl  alcohol.          Acetic  acid.  Ethyl  acetate.  Water. 


520  CONSIDERATION  OF  CARBON  COMPOUNDS. 

They  are  also  formed  by  the  action  of  hydrocarbon  chlorides  (or 
iodides)  on  salts.  For  instance  : 

C5HUC1    +    CH°)0        :    ^g)o    +    KC1 

Amyl  Potassium  Amyl  Potassium 

chloride.  formate.  formate.  chloride. 

Occurrence  in  nature.  Many  ethers  are  products  of  vegetable 
life  and  occur  in  some  essential  oils ;  wax  contains  the  compound 
ether  melissyl  palmitate,  C3(JH61.C16H31O.O,  and  spermaceti,  a  solid 
substance  found  in  the  head  of  the  whale,  is  cetyl  palmitate,  C^H^. 
C16H31O.O.  The  most  important  group  of  esters  are  the  fats  and 
fatty  oils,  which  are  distributed  widely  in  the  vegetable,  but  even 
more  so  in  the  animal  kingdom. 

General  properties.  The  ethers  and  esters  of  the  lower  members 
of  the  monatomic  alcohols  and  fatty  acids  have  generally  a  character- 
istic and  pleasant  odor.  Fruit  essences  consist  mainly  of  such  esters, 
and  what  is  generally  known  as  the  "  bouquet "  or  "  flavor  "  of  wine 
and  other  alcoholic  liquors  is  due  chiefly  to  ethers  or  compound  ethers, 
which  are  formed  during  (and  after)  the  fermentation  by  the  action 
of  the  acids  present  upon  the  alcohol  or  the  alcohols  formed.  The 
improvement  which  such  alcoholic  liquids  undergo  "  by  age  "  is  caused 
by  a  continued  chemical  action  between  the  substances  named. 

All  esters  are  neutral  substances ;  those  formed  by  the  lower  alco- 
hols and  acids  are  generally  volatile  liquids,  those  of  the  higher 
members  are  non-volatile  solids.  When  esters  are  heated  with  alka- 
lies, the  acid  combines  with  the  latter,  while  the  alcohol  is  liberated. 
(The  properties  of  the  esters,  termed  fats,  will  be  considered  further 
on.) 

One  of  the  chief  points  of  distinction  between  ethers  and  esters  is 
that  ethers  are  not  acted  on  by  alkalies,  while  esters  are  decomposed, 
an  alcohol  and  a  salt  of  the  alkali  metal  being  formed. 

Ethyl  ether,  Either,  (C2H5)2O  =  73.52  (Ether,  sulphuric  ether,  Ethyl 
oxide).  The  name  of  the  whole  group  of  ethers  is  derived  from  this 
(ethyl-)  ether,  in  the  same  way  that  common  (ethyl-)  alcohol  has 
given  its  name  to  the  group  of  alcohols.  The  name  sulphuric  ether 
was  given  at  a  time  when  its  true  composition  was  yet  unknown,  and 
for  the  reason  that  sulphuric  acid  was  used  in  its  manufacture. 

Ether  is  manufactured  by  heating  to  about  140°  C.  (284°  F.)  a 
mixture  of  1  part  of  alcohol  and  1.8  parts  of  concentrated  sulphuric 
acid  in  a  retort,  which  is  so  arranged  that  additional  quantities  of 
alcohol  may  be  allowed  to  flow  into  it,  while  the  open  end  is  connected 


ETHERS  AND  ESTERS.  521 

with  a  tube,  leading  through  a  suitable  cooler,  in  order  to  condense 
the  highly  volatile  product  of  the  distillation. 

Experiment  60.  Mix  100  grammes  of  alcohol  with  180  grammes  of  ordinary 
sulphuric  acid,  allow  to  stand  and  pour  the  cooled  mixture  into  a  flask  which 
is  provided  with  a  perforated  cork  through  which  pass  a  thermometer  and  a 
bent  glass  tube  leading  to  a  Liebig's  condenser.  Apply  heat  and  notice  that 
the  liquid  commences  to  boil  at  about  140°  C.  (284°  F.).  Distil  about  50  c.c., 
pour  this  liquid  into  a  stoppered  bottle  and  add  an  equal  volume  of  water. 
Ethyl  ether  will  separate  into  a  distinct  layer  over  the  water,  and  may  be 
removed  by  means  of  a  pipette.  Eepeat  the  washing  with  water,  add  to  the 
ether  thus  freed  from  alcohol  a  little  calcium  chloride  and  distil  it  from  a  dry 
flask,  standing  in  a  water-bath.  The  greatest  care  should  be  exercised  and  the 
neighborhood  of  flames  avoided  in  working  with  ether,  on  account  of  its 
volatility  and  the  inflammability  of  its  vapors. 

The  apparatus  described  above  for  etherification  can  be  constructed  so  as  to 
make  the  process  continuous.  This  may  be  done  by  using  with  the  boiling- 
flask  a  cork  with  a  third  aperture  through  which  a  glass  tube  passes  into  the 
liquid.  The  other  end  of  the  tube  is  connected  by  means  of  rubber  tubing 
with  a  vessel  filled  with  alcohol  and  standing  somewhat  above  the  flask.  As 
soon  as  distillation  commences  alcohol  is  allowed  to  flow  into  the  flask  at  a 
rate  equal  to  that  of  the  distillation,  keeping  the  temperature  at  about  140°  C. 
(284°  F.).  The  flow  of  alcohol  is  regulated  by  a  stop-cock. 

The  action  of  sulphuric  acid  upon  alcohol  is  not  quite  so  simple  as 
described  above  in  connection  with  the  general  methods  for  obtaining 
ethers,  where  the  final  result  only  was  given  An  intermediate  pro- 
duct, known  as  ethyl  sulphuric  acid  or  sulpho-vinic  acid,  is  formed, 
which,  by  acting  upon  another  molecule  of  alcohol,  forms  sulphuric 
acid  and  ether,  which  latter  is  volatilized  as  soon  as  formed.  The 
decomposition  is  shown  by  the  equations  : 


C2H5OH 

Su 
acid. 

C2H5OH  =  (C2H5)20 


Alcohol.  Sulphuric       Ethyl-sulphuric 

acid. 


Ethyl-sulphuric        Alcohol.  Ether.  Sulphuric 

acid.  acid. 

The  liberated  sulphuric  acid  at  once  attacks  another  molecule  of  alcohol, 
again  forming  ethyl-sulphuric  acid,  which  is  again  decomposed,  etc.  Theo- 
retically, a  given  quantity  of  sulphuric  acid  should  be  capable,  therefore,  of 
converting  any  quantity  of  alcohol  into  ether ;  practically,  however,  this  is  not 
the  case,  because  secondary  reactions  take  place  simultaneously,  and  because  the 
water  which  is  constantly  formed  does  not  all  distil  with  the  ether,  and  there- 
fore dilutes  the  acid  to  such  an  extent  that  it  no  longer  acts  upon  the  alcohol. 

Ether  thus  obtained  is  not  pure,  but  contains  water,  alcohol,  sulphurous  and 
sulphuric  acids,  etc. ;  it  is  purified  by  mixing  it  with  chloride  and  oxide  of 
calcium,  pouring  off  the  clear  liquid  and  distilling  it. 


522  CONSIDERATION  OF  CARBON  COMPOUNDS. 

The  official  ether  contains  of  ethyl-ether  96  per  cent,  and  of 
alcohol  4  per  cent.  It  is  a  very  mobile,  colorless,  highly  volatile 
liquid,  of  a  refreshing,  characteristic  odor,  a  burning  and  sweetish 
taste,  and  a  neutral  reaction  ;  it  is  soluble  in  alcohol,  chloroform, 
liquid  hydrocarbons,  fixed  and  volatile  oils,  and  dissolves  in  ten 
volumes  of  water.  Specific  gravity  is  0.716  at  25°  C.  (77°  F.); 
boiling-point  35°  C.  (95°  F.).  It  is  easily  combustible  and  burns 
with  a  luminous  flame.  When  inhaled,  it  causes  intoxication  and 
then  loss  of  consciousness  and  sensation.  The  great  volatility  and 
combustibility  of  ether  necessitate  special  care  in  the  handling  of  this 
substance  near  fire  or  light. 

Spiritus  cetheris  and  Spiritus  cetheris  compositus  are  mixtures  of  about  one 
part  of  ether  and  two  parts  of  alcohol,  3  per  cent,  of  certain  ethereal  oils  being 
added  to  the  second  preparation. 

Methyl  ether,  (CH3)20,  is  made  from  methyl  alcohol  and  sulphuric  acid.  It 
is  a  gas  at  ordinary  temperature,  but  readily  convertible  by  pressure  or  cold 
into  a  mobile  liquid. 

Methyl-ethyl  ether,  CH3.C2H5.0,  is  a  mixed  ether  which  can  be  prepared 
by  the  action  of  ethyl  iodide  upon  sodium  methylate : 

C2H6I  -f  NaOCH3  =  Nal  +  C2H5.O.CH3. 

Methyl-ethyl  ether  is  a  colorless,  highly  volatile,  and  inflammable  liquid  of 
peculiar  odor;  it  boils  at  11°  C.  (52°  F.).  It  has  been  used  as  an  anesthetic, 
and  for  that  purpose  is  sold  in  cylinders. 

Acetic  ether,  ^3ther  aceticus,  C2H5C2H.p2  =  87.4  (Ethyl  acetate). 
Made  by  mixing  dried  sodium  acetate  with  alcohol  and  sulphuric 
acid,  distilling  and  purifying  the  crude  product  by  shaking  with 
calcium  chloride  and  rectifying  : 

C2H5OH  +  NaC2H302  +  H2SO4  =  C2H5C2H3O2  +  NaHSO4  +  H2O. 
Ethyl  Sodium  Acetic  ether.        Sodium  acid 

alcohol.  acetate.  sulphate. 

Experiment  61.  Add  to  a  mixture  of  40  grammes  of  pure  alcohol  and  100 
grammes  of  concentrated  sulphuric  acid  60  grammes  of  sodium  acetate.  In- 
troduce this  mixture  into  a  boiling-flask,  connect  it  with  a  Liebig's  condenser 
and  distil  about  50  c.  c.  Eedistil  the  liquid  from  a  flask,  as  represented  in  Fig. 
69,  page  463.  and  collect  the  portion  which  passes  over  at  a  temperature  of 
IT  C.  (170°  F.) ;  it  is  nearly  pure  ethyl  acetate. 

Acetic  ether  is  a  colorless,  neutral,  and  mobile  liquid,  of  a  strong 
ethereal  and  somewhat  acetous  odor,  soluble  in  alcohol,  ether,  chloro- 
form, etc.,  in  all  proportions,  and  in  7  parts  of  water.  Specific 
gravity  0.894.  Boiling-point  about  72°  C.  (161°  F.). 


ETHERS  AND  ESTERS.  523 

Ethyl  nitrite,  C2H,NO2  =  74.51  (Nitrous  ether).     Can  be  made  by 
distilling  a  mixture  of  alcohol,  sulphuric  acid,  and  sodium  nitrite : 
C2H5OH  +  NaNOj  +  H2SO4  =  C2H6NO,  +  NaHSO<  +  H2O 

The  distillate,  which  contains,  besides  ethyl  nitrite,  some  alcohol 
and  often  some  decomposition  products,  is  washed  with  ice-cold  water, 
in  which  ethyl  nitrite  is  nearly  insoluble,  and  with  sodium  carbonate 
to  remove  traces  of  acid  ;  finally,  it  is  freed  from  water  by  treatment 
with  anhydrous  potassium  carbonate.  It  boils  at  17°  C.  (62.6°  F.). 

The  process  adopted  by  the  Pharmacopoeia  differs  from  the  former  by 
dispensing  with  the  distillation  and  using  the  insolubility  of  the  ether 
in  ice-cold  salt  solution  for  its  separation.  The  process  is  carried  out  by 
pouring  a  cold  solution  of  sodium  nitrite  very  slowly  into  an  ice-cold 
mixture  of  sulphuric  acid,  alcohol,  and  water.  Decomposition  takes 
place  as  in  the  reaction  given  above.  Some  sodium-acid  sulphate  is 
precipitated  and  has  to  be  separated  from  the  liquid,  which  is  poured 
into  a  separating  funnel  where  two  layers  form.  The  lower  aqueous 
solution  is  drawn  off  and  the  remaining  nitrous  ether  is  purified  like 
the  distillate  obtained  in  the  first  process.  (For  assay-method  of  ethyl 
nitrite,  see  paragraph  on  gas-analysis.) 

Spirit  of  nitrous  ether,  Spiritus  cetheris  nitrosi,  Sweet  spirit  of  niter. 
This  is  a  mixture  of  about  4  parts  of  ethyl  nitrite  with  96  parts 
of  alcohol.  It  is  a  clear,  mobile,  volatile,  and  inflammable  liquid,  of 
a  pale  straw  color  inclining  slightly  to  green,  a  fragrant,  ethereal 
odor,  and  a  sharp,  burning  taste.  It  is  neutral,  or  but  very  slightly 
acid  to  litmus  paper  but  evolves  no  carbon  dioxide  with  potassium 
bicarbonate. 

Amyl  nitrite,  Amylis  nitris,  C5HUNO2  =  116.24.  Made  by  a 
process  analogous  to  the  first  one  mentioned  above  for  ethyl  nitrite, 
substituting  amyl  alcohol  for  ethyl  alcohol. 

The  official  amyl  nitrite  contains  of  this  ether  about  80  per  cent., 
together  with  variable  quantities  of  undetermined  compounds ;  it  is 
a  clear,  pale-yellowish  liquid,  of  an  ethereal,  fruity  odor,  an  aromatic 
taste,  and  a  neutral  or  slightly  acid  reaction.  Specific  gravity  0.865. 
Boiling-point  96°  C.  (205°  F.).  The  low  boiling-point  necessitates 
special  precautions  in  storing  the  article.  It  is  best  kept  in  sealed 
vials  and  dispensed  in  sealed  glass  bulbs,  each  containing  only  a  few 
drops  of  the  liquid. 

Fats  and  fat  oils.  All  true  fats  are  esters  of  the  triatomic  alcohol 
glycerin,  in  which  the  three  replaceable  hydrogen  atoms  of  the  hy- 


524  CONSIDERATION  OF  CARBON  COMPOUNDS. 

droxyl  are  replaced  by  three  univalent  radicals  of  the  higher  members 
of  the  fatty  acids.     For  instance  : 

/OH 

Glycerin       =  C3H5.(OH>3  or  C3H  /OH 

\OH 

Stearicacid  =  C18H35O.OH  or  C18H35O\O 

H/ 

/(C18H350).0 

Stearin  or  tristearin  =  C3H5.(C18H35O)3.O3  or  C3H5^_(C]8H35O).O 

\(C18H350).0 

While  all  natural  fats  are  glycerin  in  which  the  three  hydrogen 
atoms  are  replaced,  we  may  by  artificial  means  introduce  but  one  or 
two  acid  radicals,  thus  forming  : 


/(C18H35O)O  /(C18H,50)O 

Monostearin  =  C3H5^OH  Distearin  =  C3H5/(C18H35O)O 

\OH 


Fats  are  often  termed  glycerides  ;  stearin  being,  for  instance,  the 
glyceride  of  stearic  acid. 

The  principal  fats  consist  of  mixtures  of  palmitin,  C3H5.(C16H31O)3. 
03,  stearin,  C3H5.(C18H35O)3.O3,  and  olein,  C^C^O^O,,. 
Stearin  and  palmitin  are  solids,  olein  is  a  liquid  at  ordinary  tem- 
perature ;  the  relative  quantity  of  the  three  fats  mentioned  determines 
its  solid  or  liquid  condition.  The  liquid  fats,  containing  generally 
olein  as  their  chief  constituent,  are  called  fatty  oils  or  fixed  oils  in 
contradistinction  to  volatile  or  essential  oils. 

All  fats,  when  in  a  pure  state,  are  colorless,  odorless,  and  tasteless 
substances,  which  stain  paper  permanently  ;  they  are  insoluble  in 
water,  difficultly  soluble  in  cold  alcohol,  easily  soluble  in  ether,  disul- 
phide  of  carbon,  benzene,  etc.  The  taste  and  color  of  fats  are  due  to 
foreign  substances,  often  produced  by  a  slight  decomposition  which 
has  taken  place  in  some  of  the  fat.  All  fats  are  lighter  than  water, 
and  all  solid  fats  fuse  below  100°  C.  (212°  F.)  ;  fats  can  be  distilled 
without  change  at  about  300°  C.  (572°  F.),  but  are  decomposed  at  a 
higher  temperature  with  the  formation  of  numerous  products,  some 
of  which  have  an  extremely  disagreeable  odor,  as,  for  instance, 
acrolem,  which  has  been  mentioned  before. 

Fats  being  lighter  than,  and  insoluble  in,  water  will  float  on  it,  but  mechani- 
cal mixtures  of  both  substances  exist  in  emulsions.  These  contain  finely  di- 
vided fat  globules,  suspended  in  the  water,  or  better  in  water  containing  some 
gum-arabic  or  a  similar  substance.  Milk  and  certain  plant  juices  are  examples 
of  natural  emulsions. 

Some  fats  keep  without  change  when  pure  ;  since,  however,  they  gen- 
erally contain  impurities,  such  as  albuminous  matter,  etc.,  they  suffer 


ETHERS  AND  ESTERS.  525 

decomposition  (a  kind  of  fermentation  aided  by  oxidation),  which  re- 
sults in  a  liberation  of  the  fatty  acids,  which  impart  their  odor  and  taste 
to  the  fats,  causing  them  to  become  what  is  generally  termed  rancid. 

Some  fats,  especially  some  oils,  suffer  oxidation,  which  renders 
them  hard.  These  drying  oils  differ  from  other  oils  in  being  mixtures 
of  olein  with  another  class  of  glycerides,  containing  unsaturated  acids 
with  less  hydrogen  in  relation  to  carbon  than  oleic  acid.  Drying  oils 
are  prevented  from  drying  by  albuminous  impurities,  which  may  be 
removed  by  treating  the  oil  with  4  per  cent  of  concentrated  sulphuric 
acid  ;  the  acid  does  not  act  on  the  fat,  but  quickly  destroys  the  albu- 
minous matters,  which,  with  the  sulphuric  acid,  sink  to  the  bottom, 
while  the  "  refined  "  oil  may  be  removed  by  decantation. 

Fats  are  largely  distributed  in  the  animal  and  vegetable  kingdoms. 
They  exist  in  plants  chiefly  in  the  seeds,  while  in  animals  they  are  found 
generally  under  the  skin,  around  the  intestines,  and  on  the  muscles. 

Human  fat,  beef  tallow,  mutton  tallow,  and  lard  are  mixtures  of 
palmitin  and  stearin  with  some  olein.  Butter  consists  of  the  glycer- 
ides of  butyric  acid,  capro'ic  acid,  caprylic  acid,  and  capric  acid, 
which  are  volatile  with  water  vapors,  and  of  myristic,  palmitic,  oleic, 
and  stearic  acids,  which  are  not  volatile. 

The  principal  non-drying  vegetable  oils  (consisting  chiefly  of  olein) 
are  olive  oil,  cottonseed  oil,  cocoanut  oil,  palm  oil,  almond  oil. 

Among  the  drying  oils  are  of  importance :  linseed  oil,  castor  oil, 
croton  oil,  hemp  oil,  cod-liver  oil. 

Whenever  fats  are  treated  with  alkaline  hydroxides,  or  with  a 
number  of  other  metallic  oxides,  decomposition  takes  place,  the  fatty 
acids  combining  with  the  metals,  while  glycerin  is  set  free.  Some 
of  the  substances  thus  formed  are  of  great  importance,  as,  for  instance, 
the  various  kinds  of  soap. 

The  term  saponification,  as  used  by  physiologists,  is  applied  to  the 
decomposition  which  occurs  when  neutral  fat  is  split  into  its  constitu- 
ents, glycerin  and  fatty  acid.  This  decomposition  is  a  hydrolytic 
cleavage,  and  can  be  produced  by  the  action  of  boiling  alkalies,  super- 
heated steam,  various  enzymes,  etc.  In  other  words,  the  formation 
of  a  soap  is  not  an  essential  part  of  the  process. 

Soap.  Any  fat  boiled  with  sodium  or  potassium  hydroxide  will 
form  soap.  Soft  soap  is  potassium  soap,  hard  soap  is  sodium  soap. 
The  better  kinds  of  hard  soap  are  made  by  boiling  olive  oil  with 
sodium  hydroxide : 

C3H5(C]8H3302)3  +  SNaOH  =  SNaC^O,  +  C3H5(OH)3. 
Oleateof  erlvceryl  Sodium          Sodium  oleate  Glycerin, 

(olive  oil).  hydroxide.         (hard  soap). 


526  CONSIDERATION  OF  CARBON  COMPOUNDS. 

Soaps  are  soluble  in  water  and  alcohol ;  they  contain  rarely  less 
than  30  per  cent.,  but  sometimes  as  much  as  70-80  per  cent,  of  water. 

Potassium  or  soft  soap  is  usually  yellowish,  but  it  is  sometimes  tinted  green 
artificially,  and  is  then  called  "green  soap."  It  contains,  besides  the  potas- 
sium salts  of  the  fatty  acids,  the  glycerin  liberated  in  the  saponification  and 
relatively  much  water.  Hard  or  sodium  soap  is  separated  from  the  solution 
after  saponification  by  adding  common  salt  to  the  boiling  mixture  to  satura- 
tion. The  soap,  being  insoluble  in  the  salt  solution,  separates  as  a  molten 
layer,  which  can  be  removed  after  cooling  and  solidifying.  This  method  of 
separating  the  soap  is  known  as  the  "salting  out"  process.  The  soap  is  free 
from  glycerin,  but  contains  some  water. 

Ammonia  liniment,  Linimentum  ammonice,  and  lime  liniment,  Lini- 
mentum  calcis,  are  obtained  by  mixing  cottonseed  oil  with  ammonia- 
water  and  lime-water  respectively.  The  oleate  of  ammonium  or 
calcium  is  formed,  and  remains  mixed  with  the  liberated  glycerin. 

Lead  plaster.  Chiefly  lead  oleate,  Pb(C18H33O2)2.  Obtained  by  boiling  lead 
oxide  with  olive  oil  and  water  for  several  hours,  until  a  homogeneous,  pliable, 
and  tenacious  mass  is  formed.  Lead  oleate  differs  from  the  oleate  of  the  alkalies 
by  its  complete  insolubility  in  water. 

Experiment  62.  Dissolve  in  a  500  c.c.  flask  15  grammes  of  potassium  hy- 
droxide in  100  c.c.  of  alcohol.  Melt  50  grammes  of  lard  in  an  evaporating  dish 
and  pour  the  liquefied  fat  into  the  flask.  Heat  over  a  water  bath,  and  shake 
cautiously  when  the  alcohol  begins  to  boil.  Saponification  takes  place  very 
rapidly,  and  its  completion  is  determined  by  pouring  a  few  drops  of  the  liquid 
into  a  test-tube  of  water,  when  any  unsaponified  fat  will  float  on  the  surface. 
When  saponification  is  complete  the  solution  contains  soap,  glycerin,  and  any 
excess  of  caustic  potash. 

Pour  the  contents  of  the  flask  into  250  c.c.  of  hot  5  per  cent,  sulphuric  acid  ; 
the  fatty  acids  separate  as  an  oily  layer  which  solidifies  on  cooling.  The  solu- 
tion contains  potassium  acid  sulphate,  sulphuric  acid,  and  glycerin.  When  the 
solution  is  neutralized,  evaporated  to  crystallization,  and  extracted  with  alco- 
hol, glycerin  can  be  obtained  by  evaporation  of  the  alcoholic  extract. 

Reactions  of  fats  and  fatty  acids. 

1.  Boil  5  grammes  of  suet  with  25  c.c.  of  alcohol  and  filter  while 
hot.     Wash  the  residue  with  a  little  ether,  squeeze  as  dry  as  possible 
and  then  dry  in  the  air.    The  resulting  fibrous  mass  is  the  connective 
tissue  network  of  the  adipose  tissue  and  a  little  fat.     Show  the  pres- 
ence of  protein  in  connective  tissue  by  the  xanthoproteic  and  Millon's 
reactions.     On  evaporation  of  the  alcoholic  filtrate,  fat  is  left. 

2.  Rub  a  little  fat  on  glazed  white  paper.    Notice  that  this  "  grease- 
spot"  appears  dark  on  a  white  background  in  reflected  light,  but 
light  (transparent)  in  transmitted  light.    The  stain  does  not  disappear 
on  heating. 


ETHERS  AND  ESTERS.  527 

3.  Heat  in  a  dry  test-tube  a  small  quantity  of  fat  with  an  equal 
portion  of  potassium  bisulphate.     Acrolein  is  formed  and  recognized 
by  its  odor. 

4.  Heat  about  2  grammes  of  fatty  acids  with  100  c.c.  of  water  and 
enough  sodium  carbonate  to  dissolve  the  fatty  acids.     A  solution  of 
sodium  soap  is  formed,  of  which  use  a  few  c.c.  for  each  of  the  follow- 
ing reactions : 

a.  Heat  with  an  excess  of  hydrochloric  acid ;  fatty  acids  are  lib- 
erated. 

6.  Add  calcium  chloride  solution  ;  insoluble  calcium  soap  is  formed, 
and  the  solution  does  not  foam  on  shaking. 

c.  Add  lead  acetate  solution  ;  a  white  precipitate  of  an  insoluble 
lead  salt  (lead  plaster)  is  formed,  becoming  sticky  on  heating. 

d.  Add  some  olive  oil  and  shake  well ;  a  homogeneous  milk-like 
mixture — i.  e.,  emulsion — is  formed. 

Wool-fat,  Lanolin,  Adeps  lanse.  This  is  the  fat,  or  a  mixture  of  fats, 
found  in  sheep's  wool  and  obtained  by  treating  the  wool  with  soap-water,  and 
acidifying  the  wash  liquor,  when  the  fats  separate  unchanged.  These  fats 
differ  from  the  fats  spoken  of  above  in  so  far  as  the  alcohol  present  is  not 
glycerin,  but  an  alcohol,  or  rather  two  isomeric  alcohols  of  the  composition 
C26H4:!OH  and  known  as  cholesterin  and  isocholesterin.  These  alcohols,  which 
are  white,  crystalline,  fusible  substances,  when  in  combination  with  fatty  acids 
form  the  compound  ethers  known  as  lanolin. 

Lanolin  is  a  yellowish-white  (or,  when  not  sufficiently  purified,  a  more  or 
less  brownish),  fat-like  substance,  having  the  peculiar  odor  of  sheep's  wool  and 
fusing  at  about  40°  C.  (104°  F.),  forming  an  oily  liquid.  Unlike  true  fats, 
lanolin  is  capable  of  mixing  with  twice  its  weight  of  water  or  aqueous  solutions 
and  yet  retaining  its  fatty  consistency ;  it  is,  moreover,  much  less  liable  to  de- 
compose than  fats,  and  it  is  this  property  and  its  power  to  mix  with  aqueous 
solutions  which  have  rendered  lanolin  a  valuable  agent  in  certain  pharma- 
ceutical preparations.  Official  is  also  hydrous  wool-fat,  the  purified  fat  mixed 
with  not  more  than  30  per  cent,  of  water. 

QUESTIONS. — Explain  the  constitution  of  simple  and  mixed  ethers  ancfr 
esters.  To  what  inorganic  compounds  are  they  analogous?  State  the  general 
processes  for  the  formation  of  ethers  and  esters.  What  is  the  composition  of 
ethyl  ether  ?  Explain  the  process  of  its  manufacture  in  words  and  symbols, 
and  state  its  properties.  How  is  acetic  ether  made,  and  what  are  its  proper- 
ties? What  is  sweet  spirit  of  niter,  and  how  is  it  made?  State  the  general 
composition  of  fats  and  the  chief  constituents  of  tallow,  butter,  and  olive  oil. 
What  is  the  solubility  of  fats  in  water,  alcohol,  and  ether;  how  do  heat  and 
oxygen  act  upon  them  ;  what  is  the  cause  of  their  becoming  rancid?  Explain 
the  composition  and  manufacture  of  soap,  and  state  the  difference  between  hard 
and  soft  soap.  How  are  ammonia  liniment,  lime  liniment,  and  lead  plaster 
made,  and  what  is  their  composition  ?  What  is  the  source  of  lanolin ;  what 
are  its  constituents  and  properties  ? 


528  CONSIDERATION  OF  CARBON  COMPOUNDS. 

48.  CARBOHYDRATES. 

General  remarks.  The  name  carbohydrates  was  originally  given 
to  a  class  of  compounds  found  chiefly  in  plants,  and  containing  in 
the  molecule  6  atoms  of  carbon  (or  a  multiple  of  6)  in  combination 
with  hydrogen  and  oxygen  in  the  proportion  to  form  water,  as  shown 
in  the  formula  for  grape-sugar,  C6H12O6,  cane-sugar,  C12H22OU,  etc. 
While  even  formerly  the  name  was  not  well  chosen,  because  it 
implies  that  these  subfetances  are  carbon  in  combination  with  water, 
to-day  it  is  still  less  suitable,  because  members  of  the  group  have  been 
found  which  do  not  contain  oxygen  and  hydrogen  in  the  proportion 
mentioned ;  as,  for  instance,  a  sugar,  termed  rhamnose,  having  the 
composition  C6H12O5.  We  also  know  now  carbohydrates  containing 
carbon  atoms  in  numbers  which  have  no  relation  to  6.  While,  there- 
fore, the  term  carbohydrate  no  longer  implies  what  it  formerly 
did,  and  no  longer  refers  to  the  restricted  number  of  compounds 
which  it  formerly  included,  yet  it  is  retained  for  the  whole  group  of 
compounds  now  to  be  considered. 

The  group  includes  now,  as  heretofore,  the  different  sugars,  starches, 
gums,  etc.,  and  also  a  number  of  compounds  obtained  by  artificial  or 
synthetical  processes.  In  order  to  show  in  its  name  that  a  substance 
belongs  to  the  carbohydrates,  the  ending  ose  is  used  to  distinguish 
these  bodies  from  the  members  of  other  groups. 

Constitution.  While  the  true  atomic  structure  of  many  carbo- 
hydrates is  as  yet  not  fully  understood,  the  structure  of  others  is 
well  known.  It  appears  that  some  carbohydrates  are  true  aldehydes, 
while  others  are  closely  related  to  ketones,  and  yet  others  are  the 
anhydrides,  or  condensation  products  of  the  former. 

Thus,  a  sugar  of  the  composition  C3H6O3,  termed  glycerose,  is  obtained  by  the 
action  of  mild  oxidizing  agents  on  glycerin,  thus : 

C3H803  +  O  =  C3H603  +  H20. 

If  we  bear  in  mind  the  fact  that  glycerin,  C3H5(OH)3,  is  a  triatomic  alcohol, 
and  that  alcohols  by  oxidation  yield  aldehydes,  we  realize  the  analogy  existing 
between  the  above  reaction  and  that  leading  to  the  formation  of  the  aldehydes, 
previously  considered. 

In  a  manner  similar  to  the  one  producing  glycerose  from  glycerin,  a  sugar 
of  the  composition  C4H8O4,  and  called  erythrose,  is  obtained  from  the  tetratomic 
alcohol  erythrite,  C4H6(OH)4,  while  a  sugar  of  the  composition  C6H12O6  is  ob- 
tainable from  the  hexatomic  alcohol  mannite,  C6H8(OH)6.  In  both  cases  two 
atoms  of  hydrogen  are  split  off  from  the  alcohol  molecules. 

The  relationship  existing  between  the  sugars  of  the  composition  C6H]2O6 


CA  RBOH  YDEA  TES.  529 

and  other  carbohydrates  having  the  composition  C6PTi0O5  or  C12H22On  can  he 
readily  shown  by  the  equations : 

*(C6H1206    -       H20)  (C6H1005)z 

2(C6H1206)-     H20         :    C12H22On, 

which  show  that  abstraction  of  water  leads  to  the  formation  of  compounds 
having  the  composition  of  starch,  C6H10O5,  and  cane-sugar,  C12H22On,  respec- 
tively. While  this  abstraction  of  water  is  difficult,  it  is  an  easy  matter  to 
cause  starch  or  cane-sugar  to  take  up  water,  with  the  result  that  sugars  of  the 
composition  C6H12O6  are  formed. 

Properties.  Carbohydrates  are  either  fermentable,  or  can,  in  most 
cases,  be  converted  into  substances  which  are  capable  of  fermentation. 
They  are  not  volatile,  but  suffer  decomposition  when  sufficiently 
heated  ;  they  have  neither  acid  nor  basic  properties,  but  are  of  a  neu- 
tral reaction.  Oxidizing  agents  convert  them  into  saccharic  and 
mucic  acids  and  finally  into  oxalic  acid.  (Soluble  carbohydrates 
have  generally  the  property  of  turning  the  plane  of  polarized  light.) 

Most  carbohydrates  are  white,  solid  substances,  and,  with  the  ex- 
ception of  a  few,  soluble  in  water.  Those  carbohydrates  belonging 
to  the  sugars  have  a  more  or  less  sweet  taste.  Many  of  them, 
especially  glucose,  are  good  reducing  agents,  as  is  shown  by  the 
fact  that  they  deoxidize  in  alkaline  solution  salts  (or  oxides)  of 
copper,  bismuth,  mercury,  gold,  etc.,  either  to  a  lower  state  of 
oxidation  or  to  the  metallic  state. 

Occurrence  in  nature.  No  other  organic  substances  are  found  in 
such  immense  quantities  in  the  vegetable  kingdom  as  the  members 
of  this  group,  cellulose  being  a  chief  constituent  of  all,  starch  and 
various  kinds  of  sugar  of  most  plants.  Carbohydrates  are  also  found 
as  products  of  animal  life,  as,  for  instance,  the  sugar  in  milk,  in  bees' 
honey,  etc. 

Classification.  The  carbohydrates  are  conveniently  divided  into 
the  following  three  groups  : 

1.  Monosaccharides,  or  simple  sugars.     To  this  group  belong  the 
sugars  which  cannot  be  broken  down  into  two  or  more  simple  sugars. 
They  contain  from  3  to  9  atoms  of  carbon,  in  most  cases  the  same 
number  of  oxygen  atoms,  and  double  the  number  of  hydrogen  atoms. 
(Dextrose,  levulose,  galactose,  etc.) 

2.  Disaccharides,  or  complex  sugars.     These  are  sugars  which,  on 
taking  up  1   molecule  of  water,  split  up  into  two  simple  sugars. 
(Cane-sugar,  maltose,  lactose,  etc.) 

3.  Polysaccharides.     These  do  not  resemble  sugars,  have  no  sweet 
taste,  and  form  simple  sugars  only  after  repeated  cleavages.  (Starches, 
gums,  cellulose,  etc.) 

34 


530  CONSIDERATION   OF  CARBON  COMPOUNDS. 

Monosaccharides. 

The  monosaocharides  are  white,  odorless,  sweet,  crystallizable,  neu- 
tral substances,  readily  soluble  in  water,  sparingly  soluble  in  alcohol, 
insoluble  in  ether.  Like  all  aldehydes  and  ketones  they  are  easily 
oxidized,  acting  as  strong  reducing  agents.  Trommer's,  Fehling's, 
and  Boettger's  "  reduction  tests  "  depend  on  this  property.  Solutions 
of  monosaccharides,  acidified  with  acetic  acid,  give  with  phenyl-hy- 
drazine  crystalline  precipitates  of  substances  called  osazones.  The  tri- 
oses,  hexoses,  and  nonoses  are  capable  of  alcoholic  fermentation,  the 
others  are  not.  Most  of  the  monosaccharides  are  optically  active. 

According  to  the  number  of  carbon  atoms  present,  the  monosaccharides  are 
again  subdivided  into  classes  called  trioses,  tetroses,  pentoses,  hexoses,  heptoses, 
octoses,  and  nonoses,  having  the  composition  C3H6O3,  C4H8O4,  C5H10O5,  C6H12CX., 
C7HUO7,  C8H1608,  and  C9H18O9,  respectively.  The  hexoses  are  the  best-known 
group,  which  is  again  subdivided  into  two  groups,  viz.,  the  aldoses,  containing 
the  alcohol  group,  CH.2OH,  and  the  aldehyde  group,  COH ;  and  the  ketoses, 
containing  the  alcohol  group  and  the  ketone  group,  CO.  The  constitution  of 
these  compounds  is  shown  thus  : 


Aldoses 


Ketoses 


Glucose  is  an  aldose-hexose,  while  fructose  is  a  ketose-hexose. 

Dextrose,  Glucose,  Grape-sugar,  C6H12O6.  This  substance  is 
very  abundantly  diffused  throughout  the  vegetable  kingdom,  and  is 
generally  accompanied  by  fruit-sugar.  It  is  contained  in  large  quan- 
tities in  the  juice  of  many  fruits;  the  percentage  of  grape-sugar  in 
the  dried  fig  is  about  65,  in  grape  10-20,  in  cherry  11,  in  mulberry  9, 
in  strawberry  6,  etc. 

Dextrose  is  found  also  in  honey  and  in  minute  quantities  in  the 
normal  blood  (0.1  per  cent,  or  less),  and  traces  occur,  perhaps,  in 
normal  urine,  the  quantity  in  both  liquids  rising,  however,  during 
certain  diseases,  as  high  as  5  per  cent,  or  higher. 

Grape-sugar  is  produced  in  the  plant  from  starch  by  the  action  of 
the  vegetable  acids  present;  it  may  be  obtained  artificially  from 
starch  (and  from  many  other  carbohydrates)  by  heating  with  dilute 
mineral  (sulphuric)  acids,  which  convert  starch  first  into  dextrin  and 


Trioses. 

Tetroses. 

Pentoses. 

Hexoses. 

f  COH 

COH 

COH 

COH 

I 
CHOH 

(CHOH), 

(CHOH)3 

(CHOH)4 

1 

| 

1 

[  CH2OH 

CH,OH 

CH.2OH 

CH.OH. 

f  CH2OH 

CH,OH 

CH2OH 

CH2OH 

1 

1 

1 

I 

CO 

CO 

CO 

CO 

1 

1 

1 

1 

CH2OH 

CHOH 

(CHOH)2 

(CHOH)3 

! 
CH,OH 

Cff,OH 

CH2OH. 

CARBOHYDRATES.  531 

then  into  grape-sugar.  Corn-starch  is  now  largely  used  for  that  pur- 
pose, the  excess  of  sulphuric  aoid  being  removed  by  treating  the  solu- 
tion with  chalk ;  the  filtered  solution  is  either  evaporated  to  a  syrup 
and  sold  as  "glucose,"  or  evaporated  to  dryness,  when  the  com- 
mercial "  grape-sugar  "  is  obtained. 

Experiment  63.  Heat  to  boiling  100  c.c.  of  a  1  per  cent,  sulphuric  acid  and 
add  to  it  very  gradually  and  with  constant  stirring  a  mixture  made  by  rub- 
bing together  25  grammes  of  starch  and  25  grammes  of  water.  Continue  to  boil 
until  iodine  no  longer  causes  a  blue  color  (which  shows  complete  conversion  of 
starch  into  either  dextrin  or  glucose),  and  until  1  c.c.  of  the  solution  is  no  longer 
precipitated  on  the  addition  of  6  c.c.  of  alcohol  (which  shows  the  conversion  of 
dextrin  into  sugar,  dextrin  being  precipitated  by  alcohol).  Apply  to  a  portion 
of  the  glucose  solution  thus  obtained,  and  neutralized  by  sodium  carbonate,  the 
tests  mentioned  below.  To  the  remaining  solution  add  a  quantity  of  precipitated 
calcium  carbonate  sufficient  to  convert  all  sulphuric  acid  into  calcium  sulphate. 
Filter,  evaporate  the  solution  to  a  syrup  and  notice  its  sweet  taste. 

Glucose  is  met  with  generally  as  a  thick  syrup  which  crystallizes 
with  difficulty,  combining  during  crystallization  with  one  molecule  of 
water;  but  anhydrous  crystals,  closely  resembling  those  of  cane- 
sugar,  are  also  known.  Glucose  is  soluble  in  its  own  weight  of 
water  and  is  less  sweet  than  cane-sugar,  the  sweetness  of  glucose  com- 
pared to  that  of  cane-sugar  being  about  3  to  5 ;  when  heated  to  170° 
C.  (338°  F.)  it  loses  water,  and  is  converted  into  glucosan,  C6H10O5 ; 
by  stronger  heating  it  loses  more  water  and  forms  caramel,  a  mixture 
of  various  substances ;  it  turns  the  plane  of  polarized  light  to  the 
right. 

By  gentle  oxidation  dextrose  is  first  converted  into  monobasic  glu- 
conic  acid,  C6H12O7  =  C5H6.(OH)5.CO2H,  and  then  into  dibasic  sac- 
charic acid,  C6H10O8  =  C4H4.(OH)4.(CO2H)2.  Further  oxidation 
results  in  the  formation  of  acids  of  lower  molecular  weight,  due  to 
splitting  up  of  the  molecules.  (Saccharic  acid  is  soluble  in  less  than 
its  own  weight  of  water.) 

Dextrose  combines  with  various  metallic  oxides  (alkalies,  alkaline 
earths,  etc.),  and  also  with  a  number  of  other  substances,  forming  a 
series  of  compounds  known  as  glucosides. 

Dextrose  may  be  recognized  analytically : 

1.  By  causing  a  bright-red  precipitate  of  cuprous  oxide,  when 
boiled  with  a  solution  of  cupric  sulphate  in  sodium  hydroxide,  to 
which  tartaric  acid  has  been  added.     (A  solution  containing  these 
three  substances  in  definite  proportions  is  known  as  Fehling's  solu- 
tion.    See  index.) 

2.  By  precipitating  metallic  silver,  bismuth,  and  mercury,  when 


532  CONSIDERATION  OF  CARBON  COMPOUNDS. 

compounds  of  these   metals  are  heated  with  it  in  the  presence  of 
caustic  alkalies. 

3.  By  easily  fermenting  when  yeast  is  added  to  the  solution,  alco- 
hol and  carbon  dioxide  being  formed  : 

C6H1206  =  2C2H5OH  +  2C02. 

4.  By  forming  with  an  excess  of  phenyl-hydrazine,  in  a  solution 
acidified  with  acetic  acid,  a  yellow  crystalline  precipitate  of  phenyl- 
dextrosazone. 

Levulose,  Fructose,  C6H12O6  (Fruit-sugar),  occurs  with  glucose  in 
sweet  fruits  and  honey  ;  it  resembles  glucose  in  most  chemical  and 
physical  properties,  but  does  not  crystallize  from  an  aqueous  solution  ; 
it  may,  however,  be  obtained  in  white  silky  needles  from  an  alcoholic 
solution ;  it  is  met  with  generally  as  a  thick  syrup,  is  about  as  sweet 
as  cane-sugar,  and  turns  the  plane  of  polarized  light  to  the  left ;  it  is 
formed  by  the  action  of  dilute  mineral  acids  or  ferments  on  cane- 
sugar,  which  latter  takes  up  water  and  breaks  up  thus : 

C]2H22On    +    H20    =    C6HI206    +    C6H1206. 
Cane-sugar.  Dextrose.  Fructose. 

Levulose  has  been  made  by  the  polymerization  of  formic  aldehyde, 
CH2O,  and  also  by  several  other  reactions. 

Mannose,  C6H12O6.  Obtained  by  the  oxidation  of  mannite ;  it  does 
not  crystallize  and  resembles  grape-sugar. 

Galactose,  C6H12O6,  is  formed  together  with  dextrose  when  either 
milk-sugar  or  gum-arabic  is  boiled  with  dilute  sulphuric  acid.  Galac- 
tose crystallizes,  reduces  an  alkaline  copper  solution,  but  does  not  fer- 
ment with  yeast. 

When  oxidized  by  heating  with  nitric  acid,  galactose  forms  galactonic  add 
and  mucic  acids,  which  are  isomeric  with  the  above-mentioned  gluconic  and 
saccharic  acids.  Mucic  acid  is  easily  distinguished  from  saccharic  acid  by 
being  almost  insoluble  in  water. 

Inosite,  C6H12O6  (Muscle-sugar).  This  compound  was  classed  with 
the  carbohydrates  on  account  of  its  sweet  taste;  its  readiness  to 
undergo  lactic  and  butyric  fermentation;  and  the  identity  of  its 
molecular  formula  with  that  of  the  hexoses.  It  has,  however,  been 
shown  that  inosite  has  an  entirely  different  constitution,  being  a  benzol 
derivative,  viz.,  hexahydroxy-benzol,  C6H6(OH)6. 

Inosite  occurs  somewhat  abundantly  in  unripe  beans  and  peas,  and 
sparingly  in  the  liquid  of  muscular  tissue ;  traces  are  found  in  urine, 
the  quantity  increasing  in  certain  diseases.  It  does  not  ferment  with 
yeast,  does  not  reduce  alkaline  copper  solution,  and  is  optically  in-- 
active. 


CARBOHYDRATES.  533 

Disaccharides. 

The  general  physical  properties  and  the  solubility  of  disaccharides 
are  identical  with  those  of  the  monosaccharides.  They  differ  from  them 
by  not  fermenting  directly  and  by  not  forming  osazones.  The  empiri- 
cal formula  is  C12H22OU.  By  treatment  with  dilute  mineral  acids  or 
by  the  action  of  certain  enzymes  they  undergo  hydrolysis — i.  e.,  take 
up  a  molecule  of  water  and  are  resolved  into  two  hexose  molecules. 
Thus,  cane-sugar  splits  up  into  dextrose  and  levulose ;  lactose  into 
dextrose  and  galactose ;  maltose  into  two  molecules  of  dextrose. 

Cane-sugar  is  dextrorotatory,  but  the  mixture  obtained  by  the  hy- 
drolysis of  cane-sugar  is  laevorotatory,  because  levulose  turns  the 
plane  of  polarization  more  to  the  left  than  dextrose  does  to  the  right. 
For  this  reason  the  mixture  is  called  inverted  sugar  and  the  hydrol- 
ysis inversion.  The  term  inversion  is  therefore  used  to  designate  the 
splitting  of  disaccharides  into  simpler  sugars.  The  building  up  of 
complex  sugars  from  simple  sugars  is  called  reversion. 

Lactose  and  maltose  reduce  alkaline  copper  solution ;  cane-sugar 
does  not. 

Cane-sugar,  Saccharum,  C12H22OU  =  339.6  (Saccharose,  Com- 
mon sugar,  Beet-sugar}.  Cane-sugar  is  found  in  the  juices  of 
many  plants,  especially  in  that  of  the  different  grasses  (sugar-cane), 
and  also  in  the  sap  of  several  forest  trees  (maple),  in  the  roots,  stems, 
and  other  parts  of  various  plants  (sugar-beet),  etc.  Plants  contain- 
ing cane-sugar  do  not  contain  free  organic  acids,  which  latter  would 
convert  it  into  grape-sugar. 

Cane-sugar  is  manufactured  from  various  plants  containing  it  by 
crushing  them  between  rollers,  expressing  the  juice,  heating  and 
adding  to  it  milk  of  lime,  which  precipitates  vegetable  albuminous 
matter.  The  clear  liquid  is  evaporated  to  the  consistency  of  a  syrup, 
which  is  further  purified  (refined)  by  filtering  it  through  bone-black 
and  evaporating  the  solution  in  "  vacuum  pans"  to  the  crystallizing- 
point;  the  mother-liquors  are  further  evaporated,  and  yield  lower 
grades  of  sugar;  finally  a  syrup  is  left  which  is  known  as  molasses. 

Cane-sugar  forms  white,  hard,  distinctly  crystalline  granules,  but 
may  be  obtained  also  in  well-formed,  large,  monocliuic  prisms.  It 
dissolves  in  0.2  part  of  boiling,  in  0.5  part  of  cold  water,  and  in  175 
parts  of  alcohol ;  when  heated  to  160°  C.  (320°  F.)  it  fuses,  and  the 
liquid,  on  cooling,  forms  an  amorphous,  transparent  mass,  known  as 
barley  sugar;  at  a  higher  temperature  cane-sugar  is  decomposed, 
water  is  evolved,  and  a  brown,  almost  tasteless  substance  is  formed, 
which  is  known  as  caramel  or  burnt  sugar.  Oxidizing  agents  act 


534  CONSIDERATION  OF  CARBON  COMPOUNDS. 

energetically  upon  cane-sugar,  which  is  a  strong  reducing  agent.  A 
mixture  of  cane-sugar  and  potassium  chlorate  will  deflagrate  when 
moistened  with  sulphuric  acid ;  potassium  permanganate  is  readily 
deoxidized  in  acid  solution ;  cane-sugar,  however,  does  not  affect  an 
alkaline  copper  solution,  and  does  not  itself  ferment ;  but  when  heated 
with  dilute  acids  or  left  in  contact  with  yeast  in  the  presence  of  vari- 
ous bacteria  it  is  decomposed  into  dextrose  and  levulose,  both  of  which 
are  fermentable.  Like  dextrose,  cane-sugar  forms  compounds  with  met- 
als, metallic  oxides,  and  salts,  which  compounds  are  known  as  sucrates. 

Experiment  64  Make  a  one  per  cent,  cane-sugar  solution ;  test  it  with 
Fehling's  solution  and  notice  that  no  cuprous  oxide  is  precipitated.  Add  to 
50  c  c.  of  the  cane-sugar  solution  5  drops  of  hydrochloric  acid  and  heat  on  a 
water-bath  for  half  an  hour.  Again  examine  the  liquid  with  Fehling's  solu- 
tion ;  a  precipitate  of  cuprous  oxide  is  now  formed,  proving  the  conversion  of 
cane-sugar  into  dextrose  (grape-sugar)  and  levulose. 

Maltose,  C12H22On,  is  obtained  by  the  action  of  diastase  on  starch. 
Diastase  is  a  substance  formed  during  the  germination  of  various 
seeds  (rye,  wheat,  barley,  etc.),  and  it  is  for  this  reason  that  grain 
used  for  alcoholic  liquors  is  converted  into  malt — i.  e.,  is  allowed  to 
germinate,  during  which  process  diastase  is  formed,  which,  acting 
upon  the  starch  present,  converts  it  into  maltose  and  dextrin  : 

3(C6H1005)     +    H20    =    C12H220U    +    C6H1006. 
Starch.  Maltose.  Dextrin. 

Maltose  is  also  formed  by  the  action  of  dilute  sulphuric  acid  upon 
starch,  and  is  hence  often  present  in  commercial  glucose ;  by  further 
treatment  with  sulphuric  acid  it  is  converted  into  dextrose.  Maltose 
crystallizes,  reduces  alkaline  copper  solutions,  and  ferments  with 
yeast. 

Melitose,  C12H22On,  is  the  chief  constituent  of  Australian  manna. 

Sugar  of  milk,  Saccharum  lactis,  C12H22On  +  H2O  =  357.48 
(Lactose).  Found  almost  exclusively  in  the  milk  of  the  mammalia. 
Obtained  by  freeing  milk  from  casein  and  fat  and  evaporating  the 
remaining  liquid  (whey)  to  a  small  bulk,  when  the  milk-sugar  crys- 
tallizes on  cooling. 

It  forms  white,  hard,  crystalline  masses ;  it  is  soluble  in  about  6 
parts  of  water  (at  15°  C.,  59°  F.)  and  in  1  part  of  boiling  water, 
insoluble  in  alcohol  and  ether;  it  is  much  harder  than  cane-sugar, 
and  but  faintly  sweet;  it  is  not  easily  brought  into  alcoholic  fermen- 
tation by  the  action  of  yeast,  but  easily  undergoes  "  lactic  fermenta- 
tion" when  cheese  is  added.  During  this  process  milk-sugar  is 


CARBOHYDRATES.  535 

converted  into  lactic  acid.    By  hydrolysis,  lactose  is  split  into  dextrose 
and  galactose. 

Milk-sugar  resembles  dextrose  in  its  action  on  alkaline  solution  of 
copper,  from  which  it  precipitates  cuprous  oxide ;  it  differs  from  it  by 
not  fermenting  with  yeast,  and  in  forming  mucic  acid  when  heated  with 
nitric  acid. 

Polysaccharid.es. 

To  the  poly saccha rides  belong  the  starches,  gums,  cellulose,  glyco- 
gen,  etc.  They  differ  from  the  two  previous  groups  by  being  insoluble 
in  water  or  soluble  with  difficulty  ;  by  not  crystallizing  and  not  being 
diffusible.  These  latter  properties  are  generally  characteristic  of  sub- 
stances of  high  molecular  weight.  By  hydrolysis  polysaccharides  split, 
forming  dextrins,  disaccharides,  and  monosaccharides ;  their  general 
composition  is  indicated  by  (C6H10O5)X,  which  means  that  the  mole- 
cules are  made  up  of  an  unknown  multiple  of  C6H10O5.  The  consti- 
tution is  unknown. 

Starch,  Amylum,  (C6H10O5)X.  Starch  is  very  widely  distributed 
in  the  vegetable  kingdom,  and  is  found  chiefly  in  the  seeds  of  cereals 
and  leguminosa?,  but  also  in  the  roots,  stems,  and  seeds  of  nearly  all 
plants. 

It  is  prepared  from  wheat,  potatoes,  rice,  beans,  sago,  arrow-root, 
etc.,  by  a  mechanical  operation.  The  vegetable  matter  containing 
the  starch  is  comminuted  by  rasping  or  grinding,  in  order  to  open 
the  cells  in  which  it  is  deposited,  and  then  steeped  in  water;  the 
softened  mass  is  then  rubbed  on  a  sieve  under  a  current  of  water 
which  washes  out  the  starch,  while  cellular  fibrous  matter  remains  on 
the  sieve;  the  starch  deposits  slowly  from  the  washings,  and  is 
further  purified  by  treating  it  with  water. 

Starch  forms  white,  amorphous,  tasteless  masses,  which  are  pecu- 
liarly slippery  to  the  touch,  and  easily  converted  into  a  powder;  it 
is  insoluble  in  cold  water,  alcohol,  and  ether;  when  boiled  with  water, 
it  yields  a  white  jelly  (mucilage  of  starch,  starch-paste)  which  cannot 
be  looked  upon  as  a  true  solution,  but  is  a  suspension  of  the  swollen 
starch  particles  in  water ;  by  continued  boiling  with  much  water  some 
starch  passes  into  solution. 

Starch,  when  examined  under  the  microscope,  is  seen  to  consist  of 
granules  differing  in  size,  shape,  and  appearance,  according  to  the 
plant  from  which  the  starch  was  obtained.  Concentric  layers,  which 
are  more  or  less  characteristic  of  starch-granules,  show  that  they  are 
formed  in  the  plant  by  a  gradual  deposition  of  starch  matter. 

The  most  characteristic  test  for  starch  is  the  dark-blue  color  which 


536  CONSIDERATION  OF  CARBON  COMPOUNDS. 

iodine  imparts  to  it  (or  better  to  the  mucilage).  This  color  is  due  to 
the  formation  of  iodized  starch,  an  unstable  dark-blue  compound  of 
the  doubtful  composition  C6H9IO5L 

Starch  is  an  important  article  of  food,  especially  when  associated,  as  in 
ordinary  flour,  with  albuminous  substances.  In  the  body  starch,  as  well  as 
other  carbohydrates,  must  be  converted  into  monosaccharides  before  being 
absorbed.  This  hydrolysis  of  starch  may  be  made  outside  the  body  acting  on 
starch  paste  with  some  diastatic  enzyme,  or  by  prolonged  boiling  with  very 
dilute  (1  per  cent.)  mineral  acid.  The  intermediate  products  of  the  hydrolysis 
are  the  same  in  either  case.  Starch  is  first  converted  into  soluble  starch  or 
amylo-dextrin,  which  gives  a  blue  color  with  iodine ;  the  soluble  starch  next 
passes  into  malto-dextrin  and  ery thro- dextrin,  giving  a  red  color  with  iodine ; 
erythro-dextrin  passes  into  malto-dextrin  and  achroo-dexfrin,  giving  no  color 
with  iodine,  but  forming  a  white  precipitate  with  alcohol.  Achroo-dextrin 
passes  into  maltose,  and  maltose  into  dextrose.  The  hydrolysis  is  a  progressive 
reaction,  all  these  compounds  being  present  in  the  solution  at  one  time. 

Dextrin,  C6H10O5  (British  gum).  This  name  is  given  to  a  mixture 
of  the  dextrins  just  mentioned,  and  formed  by  hydrolysis  of  starch 
by  means  of  diluted  acids,  or  by  subjecting  starch  to  a  dry  heat  of 
175°  C.  (347°  F.),  or  by  the  action  of  diastase  (infusion  of  malt)  upon 
starch.  Malt  is  made  by  steeping  barley  in  water  until  it  germinates, 
and  then  drying  it. 

Dextrin  is  a  colorless  or  slightly  yellowish,  amorphous  powder,  re^ 
sembling  gum-arabic  in  some  respects ;  it  is  soluble  in  water,  does  not 
reduce  alkaline  copper  solution,  and  is  colored  light  wine-red  by  iodine. 
It  is  extensively  used  in  mucilage  as  a  substitute  for  gum-arabic. 

Gums.  These  are  amorphous  substances  of  vegetable  origin, 
soluble  in  water  or  swelling  up  in  it,  forming  thick,  sticky  masses; 
they  are  insoluble  in  alcohol,  and  are  converted  into  glucose  by  boil- 
ing with  dilute  sulphuric  acid.  Some  gums  belong  to  the  saccharoses, 
others  to  the  amy loses. 

Acacia,  Gum-arabic  is  a  gummy  exudation  from  Acacia  Senegal ; 
it  consists  chiefly  of  the  calcium  salt  of  arable  acid,  C12H22OU.  Other 
gums  occur  in  the  cherry  tree,  in  linseed  or  flaxseed,  in  Irish  moss, 
in  marsh-mallow  root,  etc. 

Gum-arabic  dissolves  slowly  in  2  parts  of  water ;  this  solution 
shows  an  acid  reaction  with  litmus,  and  yields  precipitates  with  lead 
acetate  or  ferric  chloride. 

Cellulose  (C6H10O5)X,  perhaps  C18H30O15  (Plant  fibre,  Lignin). 
Cellulose  constitutes  the  fundamental  material  of  which  the  cellular 
membrane  of  vegetables  is  built  up,  and  forms,  therefore,  the  largest 
portion  of  the  solid  parts  of  every  plant ;  it  is  well  adapted  to  this 
purpose  on  account  of  its  insolubility  in  water  and  most  other  sol- 


CARBOIIYDRA  TES.  537 

vents,  its  resistance  to  either  alkaline  or  acid  liquids,  and  its  tough 
and  flexible  nature.  Some  parts  of  vegetables  (cotton,  hemp,  and 
flax,  for  instance)  are  nearly  pure  cellulose. 

Pure  cellulose  is  a  white,  translucent  mass,  insoluble  in  all  the 
common  solvents.  It  is  not  colored  blue  by  iodine. 

The  best  solvent  for  cellulose  is  an  ammoniacal  solution  of  copper  hydrox- 
ide, known  as  Schweizer's  reagent,  a  very  efficient  preparation  of  which  is 
obtained  as  follows  :  2  grammes  of  pure  crystallized  copper  sulphate  are  dis- 
solved in  100  c.c.  of  water  to  which  a  few  drops  of  a  concentrated  solution  of 
ammonium  chloride  have  been  added.  1  gramme  of  potassium  hydroxide  is 
dissolved  in  100  c.c.  of  water  and  a  little  of  a  solution  of  barium  hydroxide 
added  to  precipitate  any  carbonate  in  the  alkali.  The  two  solutions  are  mixed 
and  the  precipitate  thoroughly  washed  by  decantation  and  on  the  filter-paper. 
The  moist  copper  hydroxide  is  finally  covered  in  a  beaker  with  just  enough 
concentrated  ammonia  water  to  dissolve  it.  The  clear  solution  is  decanted  or 
filtered  through  glass  wool.  It  must  be  preserved  in  a  dark  place. 

Cellulose  is  precipitated  from  its  solution  in  Schweizer's  reagent  by  acids  as 
a  gelatinous  mass  which  forms  a  grayish  powder  when  dried. 

Treated  with  concentrated  sulphuric  acid  it  swells  up  and  gradu- 
ally dissolves  ;  water  precipitates  from  such  solutions  a  substance 
known  as  amyloid,  which  is  an  altered  cellulose  giving  a  blue  color 
with  iodine.  Upon  diluting  the  sulphuric  acid  solution  with  water 
and  boiling  it,  the  cellulose  is  gradually  converted  into  dextrin  and 
dextrose. 

Unsized  paper  (which  is  chiefly  cellulose),  dipped  into  a  mixture 
of  two  volumes  of  sulphuric  acid  and  one  volume  of  water,  forms, 
after  being  washed  and  dried,  the  so-called  "  parchment  paper," 
which  possesses  all  the  valuable  properties  of  parchment. 

Official  purified  cotton,  known  commercially  as  absorbent  cotton,  is  prepared 
from  raw  cotton  by  boiling  it  in  a  weak  solution  of  alkali  to  remove  fatty 
matter,  then  treating  it  with  a  weak  solution  of  chlorinated  lime  to  bleach  it, 
It  is  then  washed  and  dried. 

Medicated  cotton  is  usually  prepared  by  impregnating  absorbent  cotton  with 
a  solution  of  the  medicinal  agent  in  alcohol  and  glycerin,  and  drying.  The 
glycerin  is  not  volatilized  and  serves  as  an  adhesive  agent  for  retaining  the 
active  ingredient  on  the  fiber  of  the  cotton.  Benzoated,  borated,  carbolated, 
iodized,  salicylated,  and  other  medicated  cotton  is  prepared  in  this  or  a  simi- 
lar manner.  The  percentage  of  medicinal  agent  present  must  be  calculated  on 
the  basis  of  finished  product ;  thus,  25  grammes  of  10  per  cent,  borated  cotton 
should  contain  2.5  grammes  of  boric  acid,  or  10  grammes  of  5  per  cent,  carbo- 
lated cotton  should  contain  0.5  gramme  of  pure  carbolic  acid. 

Pyroxylin,  Pyroxylinum,  chiefly  cellulose  tetm-nitrate,  C12H16O6- 
(NO3)4.  (Soluble  gun-cotton,  Nitro-cellulose.)  Cellulose  has  the 


538  CONSIDERATION  OF  CARBON  COMPOUNDS. 

power  to  unite  with  acids  to  form  ethereal  salts  (esters),  thus  exhibit- 
ing alcoholic  character.  When  immersed  in  varying  mixtures  of  con- 
centrated nitric  and  sulphuric  acids,  and  for  different  lengths  of  time, 
di-,  tri-,  tetra-,  penta-,  and  hexa-nitrate  are  formed,  thus  : 

C12H20010  +  2HNO,  -  2H20  +  CuH18O8(NO,)a. 
C12H20010  +  4HN08  -  4H20  +  CUH16O6(NOS)4. 
C12H20010  +  6HN03  =  6H20  +  CUHMO4(N08)6. 

The  sulphuric  acid  used  takes  no  part  in  the  reaction,  but  facilitates 
the  same  by  absorbing  the  water  which  is  eliminated. 

The  di-,  tri-,  and  tetrad-nitrate  are  soluble  in  a  mixture  of  alcohol 
and  ether,  which  solution  is  known  as  collodion.  These  lower  soluble 
nitrates,  better  known  as  collodion  cotton,  are  official  in  the  U.  S. 
and  British  Pharmacopoeias  as  pyroxylin  ;  -colloxylin  is  also  used  as  a 
synonym  in  this  country.  In  Europe,  pyroxylin  is  applied  to  the 
higher  (penta-  and  hexa-)  nitrates,  which  are  insoluble  in  a  mixture 
of  alcohol  and  ether,  while  colloxylin  is  applied  to  the  soluble  collo- 
dion cotton.  The  penta-  and  hexa-nitrates  form  the  highly  explosive 
gun-cotton.  A  solution  of  collodion  cotton  in  molten  camphor  hard- 
ens upon  cooling  and  is  then  known  as  celluloid.  When  warmed  it 
becomes  plastic  and  can  be  molded  into  various  shapes. 

Flexible  collodion  is  a  mixture  of  collodion,  castor  oil,  and  Canada 
balsam,  which  is  much  less  constringent  than  official  collodion.  Can- 
tharidal  (blistering)  collodion  contains  extract  of  cantharides  and  has 
blistering  properties.  Styptic  collodion  contains  tannin.  For  medi- 
cation, any  substance,  soluble  in  ether,  may  be  added  to  collodion, 
such  as  iodine,  iodoform,  salicylic  acid,  croton  oil,  extract  of  Indian 
cannabis,  mercuric  chloride,  resorcin,  pyrogallol,  atropine,  etc. 

Smokeless  gunpowder  is  gun-cotton,  first  made  gelatinous  by 
acetone,  acetic  ether,  or  like  substances,  then  dried  and  granulated. 
Smokeless  powder  occupies  less  space  and  burns  more  slowly  than 
gun-cotton. 

Experiment  65.  Immerse  2  grammes  of  dry  cotton  for  ten  hours  in  a  pre- 
viously cooled  mixture  of  28  c.c.  of  nitric  acid  and  44  c.c.  of  sulphuric  acid. 
Wash  the  pyroxylin  thus  obtained  with  cold  water  until  the  washings  have  no 
longer  an  acid  reaction.  Dissolve  1  gramme  of  the  dry  pyroxylin  in  a  mixture 
of  25  c.c.  of  ether  and  8  c.c.  of  alcohol.  The  solution  obtained  is  collodion. 

Pyroxylin  in  well-closed  bottles  exposed  to  light  decomposes  with 
evolution  of  nitrous  vapors  and  a  carbonaceous  mass  is  left.  It 
should  be  kept  dry  and  in  a  carton.  The  compound  ether  nature  of 
all  cellulose  nitrates  is  shown  by  the  fact  that  the  nitric  acid  is  elimi- 


CARBOHYDRATES.  539 

nated  and  cellulose  reformed  by  the  action  of  alkalies,  of  concentrated 
sulphuric  acid,  and  by  reducing  agents.  Treated  with  a  solution  of 
a  ferrous  salt  in  hydrochloric  acid,  they  decompose  just  as  any 
nitrate,  liberating  nitric  oxide  gas. 

Glycog-en  (C6H10O5)X.  Found  exclusively  in  animals ;  it  occurs  in 
the  liver,  the  white  blood-corpuscles,  in  many  embryonic  tissues,  and 
in  muscular  tissue.  Pure  glycogen  is  a  white,  starch-like,  amorphous 
substance,  insoluble  in  alcohol.  It  forms  an  opalescent  solution  with 
water,  gives  a  red  color  with  iodine,  and  by  hydrolysis  is  converted 
into  glucose. 

Glucosides.  This  term  is  applied  to  a  group  of  substances  (chiefly 
of  vegetable  origin)  which,  by  the  action  of  dilute  acids  or  enzymes, 
are  decomposed  with  the  production  of  a  sugar,  and  one  or  two  other 
substances  not  carbohydrates.  To  this  class  of  bodies  belong  amyg- 
dalin,  digitalin,  indican,  myronic  acid,  salicin,  etc.  Some  of  these 
compounds  will  be  considered  later  on. 

49.  COMPOUNDS  CONTAINING  NITROGEN. 
Organic  compounds  may  contain  nitrogen  in  three  forms,  viz.,  as 
nitric  (or  nitrous)  acid,  ammonia,  cyanogen,  or  derivatives  of  these 
compounds. 

Derivatives  of  nitric  acid. 

Organic  compounds  containing  nitrogen  in  the  nitric  acid  form  do 
not  occur  in  nature,  but  are  obtained  exclusively  by  artificial  means, 
often  by  treatment  of  the  organic  substance  with  concentrated  nitric 
acid.  Many  of  these  compounds  are  highly  combustible  or  more  or 
less  explosive,  as,  for  instance,  cellulose  trinitrate,  mercuric  fulminate, 
and  others. 

QUESTIONS. — To  which  group  of  substances  is  the  term  "  carbohydrates  " 
applied  ?  State  the  general  properties  of  carbohydrates.  Mention  the  three 
groups  of  carbohydrates,  and  the  composition  and  characteristics  of  the  mem- 
bers of  each  group.  Mention  some  fruits  in  which  grape-sugar,  and  some 
plants  in  which  cane-sugar  is  found.  What  is  the  difference  between  grape- 
sugar  and  cane-sugar,  and  by  what  tests  can  they  be  distinguished  ?  From 
what  source,  and  by  what  process,  is  milk-sugar  obtained  ?  What  is  starch, 
what  are  its  properties,  by  what  tests  can  it  be  recognized,  and  what  substance 
is  formed  when  diastase  or  dilute  acids  act  upon  it  ?  Where  is  cellulose  found 
in  nature,  and  what  are  its  properties?  What  compounds  may  be  obtained  by 
the  action  of  nitric  acid  upon  cellulose,  and  what  are  they  used  for?  What 
substances  are  termed  glucosides  ?  Mention  some  of  the  more  important  glu- 
cosides. 


540  CONSIDERATION  OF  CARBON  COMPOUNDS. 

Nitric  or  nitrous  acid  may  combine  with  organic  bases,  forming 
salts,  such  as  strychnine  nitrate,  urea  nitrate,  etc. ;  or  with  alcohols 
when  esters  result,  such  as  glyceryl  nitrate,  ethyl  nitrite,  etc.  Some 
of  these  compounds  have  been  considered  before. 

Nitro  compounds.  These  consist  of  radicals  in  combination  with  the 
nitric  acid  residue  N02 ;  thus,  R.NO2.  They  are  isomeric  with  the  esters  of 
nitrous  acid,  but  behave  quite  differently  from  these;  for  instance,  they  yield 
no  alkali  nitrite  when  treated  with  alkalies,  as  is  the  case  when  esters  are  thus 
treated.  The  difference  in  structure  is  represented  thus : 

K— O— NO,  R— NO2, 

Nitrite.  Nitro  compound. 

The  highly  important  nitro  compounds  of  the  benzene  series  can  be 
obtained  by  treating  the  hydrocarbons  directly  with  nitric  acid;  thus: 

C6H6  +  HON02  =  C6H5N02  +  H2O. 

Nitric  acid  does  not  react  with  fatty  hydrocarbons,  but  their  nitro  deriva- 
tives can  be  obtained  by  indirect  processes,  for  instance,  by  treating  the  halo- 
gen derivatives  with  silver  nitrite: 

CH3C1        +        AgNO2        r=        CH3N02-       +        AgCl 
Methyl  chloride.  Nitro-me thane. 

This  reaction  is  anomalous,  since  we  would  expect  to  obtain  a  true  ester  of 
nitrous  acid,  corresponding  to  silver  nitrite,  whereas  the  resulting  product  is 
not  an  ester,  but  a  uitro  compound.  A  rearrangement  takes  place  during  the 
reaction  of  the  two  substances  on  each  other.  Other  cases  of  this  kind  are 
known,  for  example,  the  formation  of  organic  isocyanides  (which  see)  from 
silver  cyanide. 

Nitroso  and  isonitroso  compounds.  While  compounds  containing  the 
group  —  NO2  are  called  nitro  compounds,  those  containing  the  group  — NO  are 
termed  nitroso  derivatives,  and  those  containing  =  N  —  OH  are  known  as  iso- 
nitroso derivatives. 

When  a  compound  containing  the  group  =  CH  —  is  treated  with  nitrous  acid 
a  reaction  takes  place  which  results  in  the  formation  of  a  nitroso  compound, 
thus : 

E3.CH        +        HNO2  R3.C.NO        +        H2O. 

Nitroso  compound. 

Isonitroso  compounds  are  formed  by  the  action  of  hydroxylamine  on  alde- 
hydes or  ketones : 

H2NOH      +       £>CO       =       ^>C  =  N  — OH      +      H2O. 

Hydroxylamine.  Ketone.  Isonitroso  compound. 

Isonitroso  compounds  are  isomeric  with  nitroso  compounds;  the  different 
linkage  of  carbon  and  nitrogen  in  the  two  classes  of  compounds  is  indicated  in 
the  two  equations  given  above. 

Both  nitro  and  nitroso  compounds,  when  treated  with  nascent  hydrogen, 
yield  ammonia  derivatives,  as  will  be  shown  later.  Isonitroso  compounds  are 


COMPOUNDS  CONTAINING  NITROGEN.  541 

also  termed  oximes ;  those  obtained  from  aldehydes  are  designated  as  aldoxiine*  ; 
those  derived  from  ketones  as  acetoximes,  or  ketoximes. 

C=N— OH 
Fulminio  acid,  C2N2O2H2,  ||  ,  seems  to  be  an  isonitroso  com- 

C=N— OH 

pound.  The  free  acid  is  extremely  unstable,  but  some  of  its  metallic  salts  are 
well  known,  especially  mercuric  fulminate,  which  is  used  as  an  explosive  in  per- 
cussion caps,  etc.  It  is  made  by  adding  alcohol  to  a  solution  of  mercury  in 
nitric  acid.  Silver  fulminate  can  be  obtained  by  a  similar  process. 

Ammonia  derivatives. 

Several  groups  of  organic  compounds  are  known,  which  are  formed 
by  replacement  of  hydrogen  in  ammonia  by  different  radicals.  Ac- 
cording to  the  nature  of  the  latter  the  compounds  are  known  as 
(tin  hies,  amides,  or  amino  acids,  respectively.  There  are,  however, 
other  compounds,  such  as  the  proteins,  containing  nitrogen  in  the  am- 
monia form,  which  do  not  belong  to  either  one  of  these  three  groups. 

Formation  of  amines  and  amides.  These  substances  are  found 
as  products  of  animal  life  (urea),  of  vegetable  life  (alkaloids),  of 
destructive  distillation  (aniline,  pyridine),  of  putrefaction  (ptomaines), 
and  may  also  be  produced  synthetically — for  instance,  by  the  action 
of  ammonia  upon  the  chloride  or  iodide  of  an  alcohol  or  acid  radical: 
C2H3.I  +  NH3  =  HI  +  NH2C2H5. 

Ethyl  iodide.      Ammonia.    Hydriodic       Ethylamine. 
acid. 

C2H3O.C1     -f    2NH3    =    NH4C1    -f     NH2.C2HSO. 

Acetyl  Ammonia.       Ammonium  Acetamide. 

chloride.  chloride. 

By  using  in  the  above  reaction  two  or  three  molecules  of  ethyl 
iodide  for  one  molecule  of  ammonia,  diethyl  or  triethyl  amine  is 
formed. 

Amines  may  also  be  formed  by  the  action  of  nascent  hydrogen 
upon  the  cyanides  of  the  alcohol  radicals : 

CH3CN    +    4H    =    NH2.C2H5. 
Methyl  cyanide.  Ethyl  amine. 

They  are  also  formed  by  the  action  of  nascent  hydrogen  upon 
nitro-compounds ;  the  manufacture  of  aniline  depends  on  this  de- 
composition : 

C6H5N02    +     6H    =    2H20     +     NH2  C6H5. 
Nitro-benzene.    Hydrogen.        Water.  Phenylamine, 

or  aniline. 

Occurrence  of  organic  bases  in  nature.  The  various  organic 
basic  substances  found  in  nature  are  either  amines  or  amides.  But 


542  CONSIDERATION  OF  CARBON  COMPOUNDS. 

a  small  number  of  organic  bases  is  found  in  the  animal  system, 
urea  being  the  most  important  one.  In  plants  organic  bases  are 
frequently  met  with,  and  are  grouped  together  under  the  name  of 
alkaloids.  While  the  constitution  of  many  alkaloids  has  not  yet 
been  sufficiently  explained,  we  know  that  many  of  them  are  deriv- 
atives of  aromatic  compounds,  for  which  reason  the  consideration  of 
the  whole  group  will  be  deferred  until  benzene  and  its  derivatives 
are  spoken  of.  The  large  number  of  basic  substances  found  in  putre- 
fying matter  and  termed  ptomaines  will  also  be  considered  later  on. 


^xll  /G%H§  /xC2H5  //C2H5  /C  H3 

\  TT  \  rT  \  TT  \O    TT  \/^    TT 

U2-tL5  ^4*19 

Or 

NH3,          N(C2H5)FT2)       N(C2H5)2H,      N(C2H5V  NCH3.C2H5  C4H9. 

Ammonia.        Ethylamine.        Diethylamine.    Triethylamine.    Methyl-ethyl-butylamine. 

The  above  formulas  show  that  by  replacement  of  either  1,  2,  or  3 
hydrogen  atoms,  mono-,  di-,  or  tri-amines  are  obtained.  These  are 
also  sometimes  designated  as  primary,  secondary,  and  tertiary  amines, 
respectively.  Primary  ajnines  may  also  be  considered  as  hydrocar- 
bons, with  one  hydrogen  atom  replaced  by  the  radical  NH2,  which  is 
called  the  amine-  or  amino-group,  and  compounds  containing  it  are 
designated  as  amino  compounds.  Thus,  CH3NH2  is  amino-methane, 
or  methyl-amine.  The  radical  NH  is  known  as  the  imine-  or  imino- 
group,  and  as  this  group  occurs  in  secondary  amines,  these  are  also 
termed  imino  compounds. 

Amines  resemble  ammonia  in  their  chemical  properties ;  they  are, 
like  ammonia,  basic  substances;  they  combine  with  acids,  directly 
and  without  elimination  of  water,  thus : 


NH3    +    HC1    =    NH4C1; 

N(C2H5)3    +    HC1    =    N(C2H5)3HC1. 
Triethylamine.  Triethylamine 

chloride. 

The  methyl  amines  are  gases  at  ordinary  temperature;  the  ethyl  amines  are 
liquids.  Many  of  them  are  inflammable ;  they  have  a  strong  ammoniacal, 
fishy  odor,  are  readily  soluble  in  water,  have  strong  basic  properties  (some  of 
them  more  so  than  ammonia),  and  precipitate  metallic  salts  like  ammonia. 

The  most  important  reaction  of  primary  amines  is  that  taking  place  with 
nitrous  acid,  thus : 

CH3NH2  +  HONO  =  CH3NH3ONO  =  CH3OH   +   H2O  +  2N. 

Methyl  Nitrous  Methyl 

amine.  acid.  alcohol. 

The  reaction  shows  the  possibility  of  replacing  the  amino  group,  NH2,  by 
hydroxyl,  which  in  this  way  may  be  introduced  into  various  compounds.  The 


COMPOUNDS  CONTAINING  NITROGEN.  543 

reaction  is  analogous  to  the  decomposition  of  ammonium  nitrite  by  heat,  thus  : 
NH4ONO   ==  HOH   +   H20   +   2N. 

Aromatic  amines  behave  differently  toward  nitrous  acid,  as  will  be  shown 
later. 

Another  characteristic  reaction  which,  as  in  the  previous  case,  distinguishes 
primary  from  the  other  amines,  is  that  with  chloroform  and  alkalies,  giving  rise 
to  the  formation  of  iso-nitriles,  substances  having  a  most  disagreeable  odor. 
(See  tests  for  chloroform.)  The  reaction  is  this  : 

C2H5NH2    +    CHC1.3    =    C2H5NC    +    3HC1. 
Ethyl  amine.      Chloroform.  Ethyl  isonitrile. 

Poly-amines.  Whenever  two  or  more  ammonia  molecules  are 
linked  together  by  hydrocarbon  radicals,  this  is  indicated  by  desig- 
nating them  as  diamines,  triamines,  etc. 

Diethylene  diamine  (O2H4)2(NH)2,  (Piper  azine),  is  a  white,  crystalline 
substance,  used  medicinally  on  account  of  its  solvent  action  on  uric  acid. 

Hexamethylenamine,  Hexamethylenamina,  (CH2)6N4  =  139.18 
(Hexamdhylene  tetramine,  Urotropin).  This  compound  results  from 
the  action  of  ammonia  on  formaldehyde  : 

6CH20        +        4NH3        =        (CH2)6NA        -f-        6H2O. 

It  is  due  to  this  reaction  that  ammonia  is  used  to  remove  the 
odor  of  formaldehyde  after  its  use  as  a  disinfectant.  The  compound 
forms  colorless,  odorless  crystals,  which  are  soluble  in  1.5  parts  of 
water;  this  solution  has  an  alkaline  reaction  on  red  litmus.  On 
heating  it  sublimes  with  partial  decomposition.  When  heated  with 
diluted  sulphuric  acid,  it  is  decomposed  into  formaldehyde  and 
ammonia. 

This  substance  is  sold  under  various  trade  names,  such  as  cystogen,  amino- 
form,  formin,  uritone,  urotropin.  These  are  all  identical  with  the  official 
hexamethylenamine. 

Some  derivatives  of  hexamethylenamine  have  been  introduced  under 
special  names,  such  as  salicylate  (saliform),  bromethylate  (bromalin,  bromo- 
formin),  tannate  (tannopin  or  tannon),  iodoform  (iodoformin). 

Amides  are  substances  derived  from  ammonia  by  replacement  of 
hydrogen  atoms  by  acid  radicals.  Thus  : 


Ammonia.  Acetamide.  Diacetamide.       Carbamide  or  urea. 

Amides  also  resemble  ammonia  in  their  chemical  properties  ;  to  a 


544  CONSIDERATION  OF  C A  EBON  COMPOUNDS. 

less  extent,  however,  than  amines,  because  the  acid  radicals  have  a 
tendency  to  neutralize  the  basic  properties  of  ammonia. 

The  introduction  of  an  acid  radicle  into  ammonia  may  be  accomplished  by 
one  of  three  generally  applicable  methods: 

1.  By  heating  the  ammonium  salt  of  organic  acids, 

CH3.COONH4     =     CH3.CONH2    +     H2O. 

Acetamicle. 

2.  By  the  action  of  ammonia  on  ethereal  salts, 

CH3,COOC2H5    -f     NH3  CII3.CONH2    +     G2H5OH. 

Ethyl  acetate. 

3.  By  the  action  of  ammonia  on  acid  chlorides.     This  reaction  is  most  fre- 
quently used : 

CH3.COC1    +     NH3     =     CH3.CONH2     +     HC1.       . 
Acetyl  chloride. 

Formamide,  H.CONH2,  is  a  colorless  liquid,  obtained  by  heating  ethyl  for- 
mate with  an  alcoholic  solution  of  ammonia.  This  compound  is  of  interest 
because  it  combines  with  chloral,  forming  Chloralformamide,  Chloralformami- 
dum  (CMoralami.de},  H.CONH2.CC13CHO,  a  substance  used  as  a  hypnotic.  It 
is  a  colorless,  odorless,  crystalline  substance,  having  a  faintly  bitter  taste.  It 
is  soluble  in  about  20  parts  of  cold  water  and  in  1.5  parts  of  alcohol.  By  heat- 
ing the  aqueous  solution  to  60°  C.  (140°  F.)  it  is  decomposed  into  chloral  and 
formamide. 

Amino-acids  are  acids  in  which  hydrogen  has  been  replaced  by 
the  amino-group,  NH2.  Consequently,  amino-acids  bear  the  same 
relation  to  acids  that  amines  bear  to  hydrocarbons.  Amino-acids 
have  both  acid  and  basic  properties — i.  e.,  they  unite  with  bases  to 
form  salts  by  replacement  of  the  carboxyl  hydrogen  ;  and  they  com- 
bine with  acids  to  form  weak  salts ;  they  also  combine  with  other  salts 
to  form  double  salts. 

Amino-acids  may  be  obtained  by  the  action  of  ammonia  on  a  halo- 
gen derivative  of  an  acid  : 

CH2C1.CO2H    -f     2NH3     =     CH2.NH2.CO2H     -f     NH4C1. 
Monochloracetic  acid.  Ammo-acetic  acid. 

Amino -acetic  acid,  obtained  as  above,  is  also  known  as  glycocoll 
or  glycine.  It  is  a  product  of  the  decomposition  of  either  glycocholic 
or  hippuric  acid  by  hydrochloric  acid.  By  oxidation  amino-acetic 
acid  splits  up  thus  : 

CH2NH2C02H     -f     30    :        2CO2     -f     NH3    +     H2O. 
Amino-acids  occur  in  the  animal  system,  and  by  oxidation  suffer 


COMPOUNDS  CONTAINING   NITROGEN.  545 

the  change  indicated  above.     Ammonia  and  carbon  dioxide  unite  to 
form  ammonium  carbamate: 

2NH3        +        C02        =        NH4.NH2.CO2. 
By  removal    f  water  this  salt  is  converted  into  urea  : 
NH4.NH2.COa     =      (NH2)2CO      +     HaO. 

Amino-formic  acid  or  carbamic  acid,  NH2.COOH,  is  the  acid 
which,  in  the  form  of  the  ammonium  salt,  is  a  constituent  of  the  com- 
mercial ammonium  carbonate.  It  is  formed  by  the  direct  action  of 
carbon  dioxide  upon  ammonia,  as  shown  above. 

Urethanes  are  ethereal  salts  of  carbamic  acid,  a  class  of  comr 
pounds  having  hypnotic  properties.  The  class  name  is  derived  from 
one  member,  which  is  official  and  generally  known  as  "  Urethane." 
It  is  ethyl  urethane,  or 

Ethyl  carbamate,  ^Jthylis  carbamas,  CO.OC2H5.NH2  =  88.42. 
Obtained  by  the  action  of  alcohol  on  urea  or  on  one  of  its  salts  : 


It  is  a  white  crystalline  powder,  readily  soluble  in  water,  alcohol,  or  ether. 
Heated  with  solution  of  potassium  hydroxide,  ammonia  is  liberated,  while  the 
addition  of  sodium  carbonate  and  iodine  causes,  on  warming,  the  precipitation 
of  iodoform. 

Several  similar  compounds  have  been  introduced  under  specific  names, 
thus:  Euphorin,  or  phenyl-urethane,  C6H5NH.COOC2H5,  a  crystalline  powder, 
sparingly  soluble  in  cold  water;  neurodin,  or  acetyloxyphenyl-urethane, 

pr  >  colorless,  sparingly  soluble  crystals  ;  thermodm,  or  phe- 


nacetin-urethane,  C6H4C^    *  <COOC2H  '    colorless>    verv    sparingly  sol- 

O  FT 

uble  needles  ;  hedonal,  ormethylpropylcarbinol-urethane,  NH2.COOCH<Q  jj 

a  difficultly  soluble  white  powder. 

The  amino-acids  and  acid-amides  are  of  considerable  interest  because  many 
products  of  animal  and  plant  life  belong  to  these  classes  of  compounds.  Some 
of  these  are  considered  in  the  subsequent  chapters  on  Physiological  Chemistry, 
but  may  be  briefly  mentioned  here. 

Sarcosine,  Methyl-glycocoll,  CI^NH.CI^CC^H,  a  product  of  the 
decomposition  of  creatine,  which  is  found  in  flesh,  and  of  caffeine,  and  may  be 
obtained  by  boiling  these  compounds  with  a  solution  of  barium  hydroxide.  It 
is  much  like  glycocoll  in  properties. 

Cystine,  (SC(CH3)NH2CO2H.)2,  a  derivative  of  a-araino-propionic  acid, 
sometimes  found  in  the  sediment  of  urine  (see  Index). 
35 


546  CONSIDERATION  OF  CARBON  COMPOUNDS. 

Leucine,  a-amino-caproic  acid,  CH3.(CH2)3.OH(NH2).CO2H,  is  widely 
distributed  in  small  quantity  in  glands  of  animals  and  in  the  sprouts  of  plants. 
It  is  one  of  the  products  of  the  decomposition  of  albumins  and  gelatin  (see 
Index). 

Taurine,  Amino-ethyl-sulprionic  acid,  NH2.CH2.CH2.SO3H,  is  com- 
bined with  cholic  acid  to  form  taurocholic  acid,  which  is  one  of  the  constitu- 
ents of  bile.  It  forms  very  stable  monoclinic  prisms  (see  Index). 

Aspartic  acid,  Amino-succinic  acid,  C2H3(NH2).(CO2H)2,  occurs  in 
pumpkin  seeds,  and  is  often  formed  when  natural  compounds  are  boiled  with 
dilute  acids.  In  this  manner  it  may  be  obtained  from  casein  and  albumin.  It 
forms  prisms  difficultly  soluble  in  water.  When  treated  with  nitrous  acid,  it 
yields  malic  acid. 

CH2.CONH2 

Asparagine,  Amino-succinamic  acid,      |  occurs  in 

CH(NH2).CO2H, 

asparagus,  liquorice,  vetches,  beans,  beets,  peas,  and  in  wheat.  It  forms  large 
crystals,  difficultly  soluble  in  cold  water.  Boiling  with  acids  or  alkalies  con- 
verts it  into  aspartic  acid  and  ammonia. 

Guanidine,  (NH)C(NH2)2,  is  obtained  by  the  oxidation  of  guanine  which 
occurs  in  guano.  Guanine,  C5H3(NH2)N4O,  is  the  amirio  derivative  of  xan- 
thine  (see  Index),  which  is  closely  related  to  uric  acid,  and  which  is  found  in 
all  the  tissues  of  the  body  and  in  the  urine.  Guanidine  is  an  imide  of  urea, 
OC(NH2)2,  is  strongly  alkaline,  and  when  boiled  with  dilute  sulphuric  acid  or 
barium  hydroxide  solution  yields  urea  and  ammonia. 


Creatine,  Methyl-guanidine-acetic  acid,  (HN)C<NG|j  Q-^  QO,H 

is  found  in  the  muscles  of  all  vertebrates,  and  is  closely  related  to  guanidine 
and  to  sarcosine.  It  forms  colorless,  transparent  prisms,  soluble  in  75  parts 
of  cold  water.  When  evaporated  in  dilute  acid  solution,  it  loses  water  to 
form  the  anhydride, 

NH-CO 

Creatinine,  (HN)C\  which  forms  prisms,  readily  soluble  in 

\NCH3-CH2, 

water.  It  is  a  strong  base.  It  is  a  constant  constituent  of  urine.  Creatine  and 
creatinine  are  discussed  at  greater  length  further  on  (see  Index). 

Urea,  Carbamide,  CO(NH2)2,  is  the  amide  of  carbonic  acid.  It  occurs 
in  the  urine  and  blood  of  all  mammals,  particularly  of  carnivorous  animals. 
It  has  been  made  by  various  synthetic  methods,  but  is  most  easily  obtained 
from  urine  (see  Index).  It  crystallizes  in  rhombic  prisms,  melting  at  132°  C., 
easily  soluble  in  water  and  alcohol.  When  boiled  with  dilute  acids  or  alka- 
lies, it  yields  carbon  dioxide  and  ammonia,  thus  : 

CO(NH2)2     +     H20    :       C02    +    2NHS. 

Urea  unites  with  acids,  thus  :  urea  hydrochloride,  CO(NH2)2.HC1  ;  urea  ni- 
trate, CO(NH2)2.HNO3,  which  is  difficultly  soluble  in  nitric  acid;  urea  phos- 


COMPOUNDS  CONTAINING  NITROGEN.  547 

phate,  CO(NH,)2.H3PO4.  It  also  unites  with  metallic  oxides,  thus :  CO(NH3)a.- 
HgO,  and  also  with  salts,  of  which  HgCl2.CO(NH2)2  and  HgO.CO(NH2)2.HNO, 
are  examples. 

Ureids.  Urea  contains  ammonia  residues  and,  therefore,  acts  in  many 
respects  like  ammonia.  Thus,  one  or  more  hydrogen  atoms  of  the  NH3  groups 
can  be  replaced  by  acid  radicals,  forming  compounds  analogous  to  the  acid 
amides.  These  are  known  as  ureids.  The  following  ureids  are  of  interest. 

CO— NH, 

Oxalyl  urea,  Parabanic  acid,    |  \CO,    is  formed   when   uric 

CO— NHX 

acid  is  boiled  with  concentrated  nitric  acid,  and  also  when  a  mixture  of  urea 
and  oxalic  acid  is  treated  with  phosphorus  oxychloride,POC!3,  which  abstracts 
the  elements  of  water.  It  acts  as  an  acid,  since  the  hydrogen  of  the  NH  group 
can  be  replaced  by  metals. 

Malonyl  urea,  Barbituric  acid,  CH2<£JQ~*J|*>CO,  like  the  previous 

compound,  can  also  be  obtained  from  uric  acid,  and  synthetically  by  treating 
a  mixture  of  urea  and  malonic  acid  with  phosphorus  oxychloride.  It  breaks 
up  into  urea  and  malonic  acid  when  treated  with  an  alkali.  Closely  related 
to  it  is 

Veronal,  Diethyl-malonyl  urea,  c2H5>C<CO— NH>CO'  which  oc~ 
curs  as  a  white,  faintly  bitter,  crystalline  powder,  melting  at  191°  C.,  and  sub- 
lirnable  without  residue.  It  is  soluble  in  about  145  parts  of  water  at  20°  C.,  in 
about  12  parts  of  boiling  water,  and  readily  in  warm  alcohol.  Veronal  is  one 
of  the  most  valuable  hypnotics,  being  prompt  and  relatively  innocuous  in  small 
doses  (8  grains),  and  dangerous  only  in  large  doses. 

Uric  acid,  C5H4N4O3,  xanthine,  C5H4N4O2,  theobromine  (dimethyl-xanthine), 
C5H3(CH3)2N4O2,  and  caffeine  (theine,  trimethyl-xanthine),  C5H(CH3)3N4O2  + 
H2O,  are  all  interesting  and  important  compounds,  but  rather  complex,  for  a 
discussion  of  which  see  Index. 


Cyanogen  compounds. 

Cyanogen  itself  does  not  occur  in  nature,  but  compounds  contain- 
ing it  are  found  in  a  few  plants  (amygdalin),  and  also  in  some  animal 
fluids  (saliva  contains  sodium  sulphocyanate).  Gases  issuing  from 
volcanoes  (or  from  iron  furnaces)  sometimes  contain  cyanogen  com- 
pounds. Their  formation  from  inorganic  matter  can  be  shown  by  the 
action  of  ammonia  on  red-hot  charcoal,  when  ammonium  cyanide  and 
methane  are  generated : 

4NJEL,        -f        3C        =        2(NH4CN)        -j-        CH4. 

The  univalent  radical  cyanogen,  —  C  =  N,  or  CN,  was  the  first 
compound  radical  distinctly  proved  to  exist  by  Gay-Lussac  in  1814. 


548  CONSIDERATION  OF  CARSON  COMPOUNDS. 

The  name  cyanogen  signifies  "  generating  blue/'  in  allusion  to  the 
various  blue  colors  (Prussian  and  TurnbulPs  blue)  containing  it. 

Cyanogen  and  its  compounds  show  much  resemblance  to  the  halo- 
gens and  their  compounds,  as  indicated  by  the  composition  of  the 
following  substances : 


C1C1, 
Chlorine, 

na, 

Hydrochloric 
acid. 

KI, 

Potassium 
iodide. 

HC10, 

Hypochlorous 
acid. 

CNCN, 

Cyanogen. 

HBr, 

Hydrobromic 
acid. 

KCN, 

Potassium 
cyanide. 

HCNO, 

Cyanic  acid. 

CNC1, 

Cyanogen 
chloride. 

HCN, 

Hydrocyanic 
acid. 

AgCN, 

Silver 
cyanide. 

HCNS, 

Sulphocyanic 
acid. 

Dicyanogen,  (CN)2.  The  unsaturated  radical  CN  does  not  exist 
as  such  in  a  free  state,  but  combines  whenever  liberated  with  another 
CN,  forming  dicyanogen.  It  may  be  obtained  by  heating  mercuric 

cyanide : 

Hg(CN)2    =    Hg    +     2CN. 

It  is  a  colorless  gas,  having  an  odor  of  bitter  almonds,  and  burn- 
ing with  a  purple  flame,  forming  carbon  dioxide  and  nitrogen;  it  is 
soluble  in  water,  and  may  be  converted  into  a  colorless  liquid  by 
pressure ;  it  acts  as  a  poison,  both  to  animal  and  vegetable  life,  even 
when  present  in  but  small  proportions  in  the  air. 

Hydrocyanic  acid,  HCN  =  26.84  (Prussic  acid).  This  compound 
is  found  in  the  water  distilled  from  the  disintegrated  seeds  or  leaves 
of  amygdalus,  prunus,  laurus,  etc.  It  is  also  found  among  the  prod- 
ucts of  the  destructive  distillation  of  coal,  and  is  formed  by  a  great 
number  of  chemical  decompositions.  For  instance  : 

By  the  action  of  ammonia  on  chloroform  : 

CHC13    +     NH3    :       HCN     +     3HC1. 
Chloroform.  Hydrocyanic     Hydrochloric 

acid.  acid. 

By  heating  ammonium  formate  to  200°  C.  (392°  F.)  : 

NH4CH02    :       HCN    +    2H20. 
Ammonium       Hydrocyanic         Water, 
formate.  acid. 

By  the  action  of  hydrogen  sulphide  upon  mercuric  cyanide  : 

Hg(CN),     +    H2S    =    :    HgS     +    2HCN. 


COMPOUNDS  CONTAINING  NITROGEN.  549 

By  the  decomposition  of  alkali  cyanides  by  diluted  acids  : 

KCN     4-    HC1    =    KC1     +    HCN. 
By  the  action  of  hydrochloric  acid  upon  silver  cyanide  : 

AgCN     +     HC1    =    AgCl    -f    HCN. 
By  distilling  potassium  ferrocyanide  with  diluted  sulphuric  acid : 

2K4Fe(CN)6    +     6(H2SO4)  K2Fe2(CN)6    +    6KHSO4    +    6HCN. 

Potassium  Sulphuric  Potassium  ferrous     Potassium  acid     Hydrocyanic 

ferrocyanide.  acid.  ferrocyanide.  sulphate.  acid. 

Experiment  66.  Place  20  grammes  of  potassium  ferrocyanide  and  40  c.c.  of 
water  into  a  boiling-flask  of  about  200  c.c.  capacity ;  provide  the  flask  with  a 
funnel-tube  and  connect  it  with  a  suitable  condenser,  the  exit  of  which  should 
dip  into  60  c.c.  of  diluted  alcohol,  contained  in  a  receiver,  which  latter  should 
be  kept  cold  by  ice  during  the  operation.  After  having  ascertained  that  all 
the  joints  are  tight,  add  through  the  funnel-tube  a  previously  prepared  mixture 
of  15  grammes  of  sulphuric  acid  and  20  c.c.  of  water.  Apply  heat  and  slowly 
distil  until  there  is  little  liquid  left  with  the  salts  remaining  in  the  flask. 

Determine  the  strength  of  the  alcoholic  solution  of  hydrocyanic  acid  thus 
prepared  volumetrically  and  dilute  it  with  water  until  it  contains  exactly  two 
per  cent,  of  HCN. 

Pure  hydrocyanic  acid  is,  at  a  temperature  below  26°  C.  (78.8°  F.), 
a  colorless,  mobile  liquid,  of  a  penetrating,  characteristic  odor  resem- 
bling that  of  bitter  almonds ;  it  boils  at  26.5°  C.  (80°  F.)  and  crystal- 
lizes at  — 15°  C.  (5°  F.).  It  is  readily  soluble  in  water,  and  a  2  per 
cent,  solution  is  the  diluted  hydrocyanic  acid,  Acidum  hydrocyanicum 
dilutam. 

According  to  the  U.  S.  P.,  this  diluted  acid  is  made  by  the  decom- 
position of  6  grammes  of  silver  cyanide  by  15.54  c.c.  of  diluted  hy- 
drochloric acid,  mixed  with  44.10  c.c.  of  water,  allowing  the  silver 
chloride  to  subside  and  pouring  off  the  clear  liquid. 

The  diluted  acid  has  the  characteristic  odor  of  bitter  almonds,  a 
slightly  acid  reaction,  and  is  completely  volatilized  by  heating.  Pure 
absolute  hydrocyanic  acid  may  be  kept  unchanged,  but  when  water 
or  ammonia  is  present,  the  acid  decomposes  comparatively  rapidly, 
giving  ammonia,  formic  acid,  oxalic  acid,  and  other  products.  The 
official  2  per  cent,  acid  deteriorates  appreciably  within  several  weeks, 
and,  therefore,  should  not  be  kept  in  stock  for  a  long  time,  but  should 
be  prepared  as  it  is  needed. 

The  salts  of  hydrocyanic  acid  are  called  cyanides,  and  are  nearly 
all  insoluble  in  water.  The  cyanides  of  the  alkali  metals,  the  alka- 
line-earth metals,  and  of  mercury  are  soluble. 

Dissociation  of  cyanogen  compounds.  Hydrocyanic  acid  is  an  extremely 
weak  acid,  and  its  aqueous  solution  conducts  electricity  very  badly,  that  is,  it 


550  CONSIDERATION  OF  CARBON  COMPOUNDS. 

has  a  very  low  conductivity,  due  to  its  extremely  small  degree  of  dissociation. 
In  a  tenth-normal  solution  at  18°  C.,  only  0.01  per  cent,  of  the  acid  molecules 
are  dissociated,  thus : 

HCN  ^±  H-  f  CN'. 

As  in  the  case  of  the  mercury  salts,  the  poisonous  character  of  hydrocyanic 
acid  and  its  salts  depends  upon  the  degree  of  dissociation  into  CNX  ions.  A 
number  of  complex  cyanides  are  known,  in  which  the  cyanogen  groups  are 
combined  with  metals  to  form  complex  radicals,  in  which  both  the  cyanogen 
and  the  metals  are  masked,  and  do  not  respond  to  the  usual  analytical  reagents. 
The  best  examples  of  such  compounds  are  the  ferrocyanide  and  ferricyanide  of 
potassium,  K4FeCN6  and  K3Fe(CN)6,  respectively.  These  compounds  are  not 
poisonous  because  they  do  not  form  CNX  ions,  being  dissociated  in  solution 
according  to  the  following  equations : 

K4Fe(CN)6  ^±  4K-  +  Fe(CN)6"" 

Ferrocyanogen  ion. 

K3Fe(CN)6  ^±  3K-  +  Fe(CN)6'" 

Ferricyanogen  ion. 

The  alkali  cyanides  are  decomposed  by  such  a  weak  acid  as  carbonic  acid, 
hence  they  have  the  odor  of  hydrocyanic  acid,  due  to  the  action  of  the  carbonic 
acid  of  the  atmosphere.  In  aqueous  solution  they  have  a  strong  alkaline  re- 
action, due  to  hydrolysis : 

KCN  ;±  K-         +  CN'\  _  TTPV 
HOH  ^±  (OH)/  +     H-  /  ' 

The  action  is  due  to  the  extremely  weak  dissociating  power  of  hydrocyanic 
acid  (see  Chapter  15). 

For  peculiarities  of  mercury  cyanide  see  chapter  on  Mercury. 

Potassium  cyanide,  Potassii  cyanidum,  KCN  —  64.7.  The  pure 
salt  may  be  obtained  by  passing  hydrocyanic  acid  into  an  alcoholic 
solution  of  potassium  hydroxide.  The  commercial  article,  however, 
Is  a  mixture  of  potassium  cyanide  with  potassium  cyanate.  It  is 
obtained  by  fusing  potassium  ferrocyanide  with  potassium  carbonate 
in  a  crucible,  when  potassium  cyanide  and  cyanate  are  formed,  while 
carbon  dioxide  escapes,  and  metallic  iron  is  set  free  and  collects  on 
the  bottom  of  the  crucible.  The  decomposition  is  as  follows  : 

K4Fe(CN)6    -f     K2CO3    ±=    5KCN     +     KCNO     +     Fe    +     CO2. 
Potassium  Potassium         Potassium          Potassium  Iron.  Carbon 

ferrocyanide.  carbonate.         cyanide.  cyanate.  dioxide. 

A  mixture  of  pure  potassium  and  sodium  cyanides,  free  from  cyanate, 
is  now  manufactured  on  a  large  scale  by  heating  together  anhydrous 
potassium  ferrocyanide  and  metallic  sodium  : 

K4Fe(CN)6  -f  2Na  =  2NaCN  +  4KCN  +  Fe. 

Potassium  cyanide,  U.  S.  P.,  should  contain  at  least  95  per  cent,  of 
potassium  cyanide ;  it  is  a  white^  deliquescent  substance,  odorless  when 


COMPOUNDS  CONTAINING  NITROGEN.  551 

perfectly  dry,  but  emitting  the  odor  of  hydrocyanic  acid  when  moist ; 
it  is  soluble  in  about  2  parts  of  water ;  this  solution  has  an  alkaline 
reaction  but  is  unstable,  decomposition  soon  taking  place  with  the 
formation  of  potassium  formate  and  ammonia,  along  with  other 

products : 

KCN  +  2H2O  =  CHK02  +  NH3. 

A  solution  of  potassium  cyanate  decomposes  slowly  in  the  cold, 
but  rapidly  on  heating,  with  the  formation  of  potassium  and  ammo- 
nium carbonates : 

2KCNO    +    4H2O    =    K2CO3    +    (NH4)2CO8. 

Potassium  cyanides  and  other  alkali  cyanides  show  a  tendency  to 
combine  with  the  cyanides  of  heavy  metals,  forming  a  number  of 
double  cyanides,  such  as  the  cyanide  of  sodium  and  silver,  NaCN. 
AgCN,  etc.,  which  are  soluble  in  water.  Hence,  precipitates  formed  by 
addition  of  alkali  cyanides  to  solutions  of  metallic  salts,  are  dissolved 
in  excess  of  the  reagent.  Double  cyanides  of  silver  and  gold  are  used 
in  commercial  electroplating.  A  large  proportion  of  the  alkali  cyanides 
manufactured  is  used  in  extracting  gold  from  its  ores,  especially  in 
Transvaal.  In  1889  not  more  than  50  tons  of  cyanide  per  annum 
were  consumed,  while  in  1905  the  consumption  was  about  10,000  tons, 
one-third  of  which  was  used  in  Transvaal. 

Silver  cyanide,  Argenti  cyanidum,  AgCN  =  132.96.  A  white 
powder,  obtained  by  precipitating  a  solution  of  potassium  cyanide 
with  silver  nitrate.  It  is  insoluble  in  water,  slowly  soluble  in  ammonia 
water,  sodium  thiosulphate,  and  potassium  cyanide  •  when  heated  it 
evolves  cyanogen,  metallic  silver  being  left. 

Mercuric  cyanide,  Hg(CN)2.  A  white  crystalline  salt,  obtained  by 
dissolving  mercurous  oxide  in  hydrocyanic  acid  ;  it  is  soluble  in  water 
and  alcohol  and  evolves  cyanogen  when  heated. 

Mercuric  oxycyanide,  Hg(ON)2.HgO.  (Basic  mercuric  cyanide.)  This  is 
obtained  by  triturating  mercuric  oxide,  dilute  sodium  hydroxide  solution,  and 
mercuric  cyanide  until  the  mixture  becomes  colorless.  The  salt  is  purified  by 
washing  with  cold  water,  or  recrystallizing  from  hot  water.  It  occurs  as  a 
white,  crystalline  powder,  soluble  in  17  parts  of  water,  and  turns  red  litmus 
blue.  It  is  recommended  as  a  substitute  for  mercuric  chloride,  as  it  is  claimed 
to  have  greater  antiseptic  power,  to  be  less  irritating,  and  to  have  no  corroding 
action  on  steel  instruments. 

Analytical  reactions  for  hydrocyanic  acid. 

(Potassium  cyanide,  KCN,  may  be  used.) 

1.  Hydrocyanic  acid,  or  soluble  cyanides,  give  with  silver  nitrate 
a  white  precipitate  of  silver  cyanide,  which  is  sparingly  soluble  in 


552  CONSIDERATION  OF  CARBON  COMPOUNDS. 

ammonia,  soluble  in  alkali  cyanides  or  thiosulphates,  but  insoluble 
in  diluted  nitric  acid. 

HCN    +    AgNO3    =    AgCN    -f    HNO3. 

2.  Hydrocyanic  acid,  mixed  with  yellow  ammonium   sulphide  and 
evaporated  to  dry  ness,  forms  sulphocyanic  acid,  which,   upon  being 
slightly  acidulated  with  hydrochloric*acid,  gives  with  ferric  chloride 
a  blood-red  color  of  ferric  sulphocyanate.     (Excess  of  ammonium 
sulphide  must  be  avoided.) 

3.  Hydrocyanic  acid,  or  soluble  cyanides,  give,  when  mixed  with 
ferrous  and  ferric  salts  and  potassium  hydroxide,  a  greenish  precipi- 
tate, which,  upon  being  dissolved  in  hydrochloric  acid,  forms  a  pre- 
cipitate of  Prussian  blue,  Fe4(FeC6]S"6)3.     This  reaction  depends  on 
the  formation  of  potassium  ferrocyanide  by  the  action  of  the  cyanogen 
upon  both  the  potassium  of  the  potassium  hydroxide  and  the  iron  of 
the  ferrous  salt.     In  alkaline  solutions,  the  blue  precipitate  does  not 
form,  for  which  reason  hydrochloric  acid  is  added. 

4.  Hydrocyanic  acid  heated  with  dilute  solution  of  picric  acid  gives 
a  deep-red  color  on  cooling. 

In  cases  of  poisoning,  the  matter  under  examination  is  distilled  (if  neces- 
sary after  the  addition  of  water)  from  a  retort  connected  with  a  cooler.  To 
the  distilled  liquid  the  above  tests  are  applied.  If  the  substance  under  ex- 
amination should  have  an  alkaline  or  neutral  reaction,  the  addition  of  some 
sulphuric  acid  may  be  necessary  in  order  to  liberate  the  hydrocyanic  acid. 
The  objectionable  feature  to  this  acidifying  is  the  fact  that  non-poisonous 
potassium  ferrocyanide  might  be  present,  which  upon  the  addition  of  sulphuric 
acid  would  liberate  hydrocyanic  acid.  In  cases  where  the  addition  of  an  acid 
becomes  necessary,  a  preliminary  examination  should,  therefore,  decide 
whether  or  not  ferro-  or  ferricyanides  are  present. 

Antidotes.  Hydrocyanic  acid  is  a  powerful  poison  both  when  inhaled  or 
swallowed  in  the  form  of  the  acid  or  of  soluble  cyanides.  As  an  antidote  is 
recommended  a  mixture  of  ferrous  sulphate  and  ferric  chloride  with  either 
sodium  carbonate  or  magnesia.  The  action  of  this  mixture  is  explained  ia 
the  above  reaction  3,  the  object  being  to  convert  the  soluble  cyanide  into  an 
insoluble  ferrocyanide  of  iron.  In  most  cases  of  poisoning  by  hydrocyanic 
acid  there  is,  however,  no  time  for  the  action  of  such  an  antidote,  in  conse- 
quence of  the  rapidity  of  the  action  of  the  poison,  and  the  treatment  is  chiefly 
directed  to  the  maintenance  of  respiration  by  artificial  means. 

About  ten  years  ago,  hydrogen  dioxide  was  proposed  as  an  antidote,  by 
which  hydrocyanic  acid  is  converted  into  the  harmless  oxamide,  CONH2 — 
CONH2.  A  solution  of  hydrogen  dioxide  is  introduced  into  the  stomach  and 
then  siphoned  out.  It  is  also  used  subcutaneously.  In  case  a  cyanide  is  the 
poison,  vinegar  may  be  mixed  with  the  hydrogen  dioxide  solution  given  inter- 
nally in  order  to  liberate  the  hydrocyanic  acid. 

Cyanogen  derivatives  obtained  directly  from  nitrogen  of  the  atmos- 


COMPOUNDS  CONTAINING  NITROGEN.  553 

phere.  When  calcium  carbide  is  heated  'to  redness  in  contact  with  nitrogen, 
calcium  cyanamide  is  formed,  thus : 

CaC2  +  2N  =  CN.NCa  +  C. 

This  substance  is  an  excellent  fertilizer,  and  is  manufactured  in  large  quanti- 
ties and  sold  under  the  name  of  nitrolim  or  lime-nitrogen  (Kalkstickstoff).  It 
is  slowly  decomposed  in  the  soil  by  moisture  and  carbon  dioxide  into  calcium 
carbonate  and  cyanamide : 

CN.NCa  4-  H20  -f  CO2  =  CaCO3  +  CN.NH2. 
The  cyanide  is  further  decomposed  probably  into  urea : 
CN.NH2  -f  H20  =  CO(NH2)2. 

Steam  under  high  pressure  converts  all  of  the  nitrogen  of  calcium  cyanamide 
into  ammonia,  which  thus  furnishes  a  method  of  obtaining  ammonia  from  at- 
mospheric nitrogen. 

When  mixed  with  sodium  carbonate  and  fused,  calcium  cyanamide  forms 
sodium  cyanide.  By  the  action  of  acids  on  the  calcium  compound,  cyanamide, 
CN.NH2,  is  formed,  which  easily  polymerizes  to  the  beautifully  crystallized 
dicyandiamide,  C2N2.N2H4,  which  is  now  made  by  the  ton  and  used  for  various 
purposes.  It  can  very  easily  be  made  to  unite  with  water  to  form  urea,  which 
is  manufactured  thus  in  great  quantities. 

Barium  carbide,  when  heated  in  nitrogen,  acts  differently  from  calcium  car- 
bide, forming  barium  cyanide,  thus: 

BaC2  +  2N  =  Ba(CN)2. 

Cyanic  acid,  HCNO,  and  Sulphocyanic  acid,  HCNS,  are  both 
colorless  acid  liquids,  the  salts  of  which  are  known  as  cyanates  and 
mlpho-cyanates.  These  salts  are  obtained  from  alkali  cyanides  by 
treating  them  with  oxidizing  agents  or  by  boiling  their  solutions  with 
sulphur,  when  either  oxygen  or  sulphur  is  taken  up  by  the  alkali 
cyanide : 

KCN     +     O    =    KCNO    =    Potassium  cyanate. 

KCN  -f  S  =  KCNS  =  Potassium  sulphocyanate. 
The  acids  themselves  are  obtained  by  indirect  processes,  as  they 
decompose  when  the  salts  are  treated  with  mineral  acids.  Sulpho- 
cyanates  give  with  ferric  salts  a  deep-red  color,  which  is  not  affected 
by  hydrochloric  acid,  but  disappears  on  the  addition  of  mercuric 
chloride. 

Metallocyanides.  Cyanogen  not  only  combines  with  metals  to 
form  true  cyanides,  which  may  be  looked  upon  as  derivatives  of 
hydrocyanic  acid,  but  cyanogen  also  enters  into  combination  with 
certain  metals  (chiefly  iron),  forming  a  number  of  complex  radicals, 
Which  upon  combining  with  hydrogen  form  acids,  or  with  basic 
elements  form  salts.  It  is  a  characteristic  feature  of  the  compound 
cyanogen  radicals,  thus  formed,  that  the  analytical  characters  of  the 


554  CONSIDERATION  OF  CARBON  COMPOUNDS. 

metals  (iron,  etc.)  entering  into  the  radical  are  completely  hidden. 
Thus,  the  iron  in  ferro-  or  ferricyanides  is  not  precipitated  by  either 
alkalies,  soluble  carbonates,  ammonium  sulphide,  or  any  of  the  com- 
mon reagents  for  iron,  and  its  presence  can  only  be  demonstrated  by 
these  reagents  after  the  organic  nature  of  the  compound  has  been 
destroyed  by  burning  it  (or  otherwise),  when  ferric  oxide  is  left, 
which  may  be  dissolved  in  hydrochloric  acid  and  tested  for  in  the 
usual  manner. 

The  principal  iron-cynogen  radicals  are  ferrocyanogen  [Feu 
(CN),,1]*,  and  ferricyanogen  [Fe^CNy]111.  These  two  radicals  con- 
tain iron  in  the  ferrous  and  ferric  state  respectively,  and  form,  upon 
combining  with  hydrogen,  acids  which  are  known  as  hydroferroeyanic 
acid,  H4Fe(CN)6  (tetrabasic),  and  hydroferricyanic  acid,  H3Fe(CN)g 
(tribasic)  ;  the  salts  of  these  acids  are  termed  ferrocyanides  and  ferri- 
cyanides. (For  dissociation  of  these,  see  p.  549.) 

Potassium  ferrocyanide,  Potassii  ferrocyanidum,  K4Fe(CN)6. 
3H2O  =  419.62  (  Yellow  prussiate  of  potash).  This  salt  is  manu- 
factured on  a  large  scale  by  heating  refuse  animal  matter  (waste 
leather,  horns,  hoofs,  etc.)  with  potassium  carbonate  and  iron  (filings, 
etc.).  The  fused  mass  is  boiled  with  water,  and  from  the  solution 
thus  formed  the  crystals  separate  on  cooling. 

The  nitrogen  and  carbon  of  the  organic  matter  (heated  as  above 
stated)  combine,  forming  cyanogen,  which  enters  into  combination 
first  with  potassium  and  afterward  with  iron. 

Potassium  ferrocyanide  forms  large,  translucent,  pale  lemon-yellow, 
soft,  odorless,  non-poisonous,  neutral  crystals,  easily  dissolving  in 
water,  but  insoluble  in  alcohol. 

Analytical  reactions  : 

1.  Ferrocyanides  heated  on  platinum  foil  burn  and  leave  a  residue 
of  (or  containing)  ferric  oxide. 

2.  Ferrocyanides  heated  with  concentrated  sulphuric  acid  evolve 
carbonic  oxide  ;  with  dilute  sulphuric  acid  liberate  hydrocyanic  acid  ; 
with  concentrated  hydrochloric  acid  liberate  hydroferroeyanic  acid. 

3.  Soluble  ferrocyanides  give  a  blue  precipitate  with  ferric  salts 
(Plate  L,  5)  : 


3K4Fe(CN)6    +     4FeCl3    =    12KC1    +     Fe4(FeC6N8)3. 

Potassium  Ferric  Potassium  Ferric  ferro- 

ferrocyanide.  chloride.  chloride.  cyanide. 

The  blue  precipitate  of  ferric  ferrocyanide,  or  Prussian  blue,  is 
insoluble   in   water  and  diluted  acids,  soluble  in  oxalic  acid  (blue 


COMPOUNDS  CONTAINING  NITROGEN.  5§5 

ink),  and  is  decomposed  by  alkalies  with  separation  of  brown  ferric 
hydroxide  and  formation  of  potassium  ferrocyanide.  The  addition 
of  an  acid  restores  the  blue  precipitate. 

4.  Soluble  ferrocyanides  give  with  cupric  solutions  a  brownish-red 
precipitate  of  cupric  ferrocyanide.     (Plate  III.,  5.) 

5.  Soluble  ferrocyanides  produce,  with  solutions  of  silver,  lead,  and 
zinc,  white  precipitates  of  the  respective  ferrocyanides. 

6.  Ferrocyanides  give  with   ferrous  salts  a  white  precipitate  of 
ferrous  ferrocyanide,  soon  turning  blue  by  absorption  of  oxygen. 
(Plate  I.,  4.) 

Potassium  ferricyanide,  K3Pe(CN)G  (Red  prussiate  of  potash).  Ob- 
tained by  passing  chlorine  through  solution  of  potassium  ferrocyanide: 

K4Fe(CN)6     -f      Cl      =      KC1      +       K3Fe(CN)6. 

Potassium  Chlorine.       Potassium  Potassium 

ferrocyanide.  chloride.  ferricyanide. 

While  apparently  this  decomposition  consists  merely  in  a  removal 
of  one  atom  of  potassium  from  one  molecule  of  potassium  ferro- 
cyanide, the  change  is  actually  more  complete,  as  the  atoms  arrange 
themselves  differently,  the  iron  passing  also  from  the  ferrous  to  the 
ferric  state. 

Potassium  ferricyanide  crystallizes  in  red  prisms,  soluble  in  water. 
It  forms,  with  ferrous  solutions,  a  blue  precipitate  of  ferrous  ferricy- 
anide, or  TurnbuWs  blue  : 

2K3Fe(CN)6  +  3FeSO4  =  3K2SO4  +  Fe3Fe2(CN)12. 

With  ferric  solutions  no  precipitate  is  produced  by  potassium  ferri- 
cyanide, but  the  color  is  changed  to  a  deep  brown. 

Sodium  nitroferricyanide,  Na2Fe(CN)5N0.2H2O.  (Sodium  nitroprusside.) 
This  is  a  salt  of  nitroferricyanic  acid,  which  is  obtained  by  the  action  of  nitric 
acid  on  potassium  ferrocyanide.  Potassium  nitrate  is  crystallized  out  by  con- 
centrating and  cooling  the  solution,  which  is  then  neutralized  by  sodium  car- 
bonate, and  the  sodium  salt  crystallized.  Addition  of  alcohol  increases  the 
separation  of  potassium  nitrate.  The  salt  forms  large  ruby-red  crystals,  solu- 
ble in  2.5  parts  of  water  and  in  alcohol.  The  aqueous  solution  decomposes  on 
standing.  It  serves  as  a  delicate  test  for  soluble  sulphides  (but  not  free  H2S), 
giving  a  purple  color  which  quickly  passes  into  violet.  It  is  also  used  as  a  test 
for  acetone  (Legal's  test). 

Cyanides  and  isocyanides  of  organic  radicals.  Only  one  form  of  hydro- 
cyanic acid  and  of  metallic  cyanides  is  known,  but  among  organic  cyanide* 
two  isomeric  forms  exist,  known  respectively  as  cyanides  or  nitrites,  and  isocyan- 
ides or  carbylamines.  Experiments  show  that  the  constitution  of  these  com- 
pounds is  represented  by  the  formulas  : 


R-C=N, 

Cyanide.  Isocyanide. 


556  CONSIDERATION  OF  CARBON  COMPOUNDS. 

In  one  case  the  organic  radical  is  in  combination  with  carbon ;  in  the  other, 
with  nitrogen.  These  compounds  are  apparently  esters  of  hydrocyanic  acid, 
but  they  behave  quite  differently  from  esters,  as  they  do  not  yield  alcohols  or 
metallic  cyanides  on  treatment  with  alkalies. 

Cyanides  or  nitriles.  These  may  be  formed  by  heating  together  iodides 
of  hydrocarbon  radicals  with  potassium  cyanide : 

CH8I  +  KCN  =  CH3CN  +  KI. 

The  cyanides  are  volatile  liquids  or  solids.  When  heated  with  water  in 
presence  of  mineral  acids  or  alkalies,  they  yield  organic  acids,  thus : 

CH3.CN  +  2H20  =  CH3.C02H  4-  NH3. 
Methyl  Acetic  acid, 

cyanide. 

This  is  an  important  reaction,  as  it  furnishes  a  simple  means  of  introducing 
carboxyl  into  compounds,  thus  forming  organic  acids.  For  this  reason  the 
cyanides  are  called  nitriles  of  the  acids,  just  as  the  acid  oxides  are  called  an- 
hydrides of  the  corresponding  acids.  Thus,  methyl  cyanide  is  called  aceto- 
nitrile,  because  it  yields  acetic  acid.  In  fact,  the  ammonium  salts  of  organic 
acids,  by  abstraction  of  water,  yield  cyanides : 

CHS.CO2NH4  =  CH8.CN  +  2H2O. 

Isocyanides  or  carbylamines.  These  compounds  are  distinguished  by  a 
disgusting  odor.  They  are  formed  by  heating  silver  cyanide,  instead  of  potas- 
sium cyanide,  with  iodides  of  hydrocarbon  radicals,  thus : 

CH3I  +  AgCN  =  CH3NC  +  Agl. 

It  is  strange,  and  as  yet  not  explained,  why  hydrocarbon  iodides  produce 
cyanides  with  potassium  cyanide,  and  isocyanides  with  silver  cyanide. 

Isocyanides  are  also  formed  by  heating  together  chloroform,  primary  amines, 
and  an  alkali,  as  shown  above  in  the  paragraph  on  amines. 

The  isocyanides  behave  differently  from  the  cyanides  when  heated  with 
water  and  acids,  thus : 

CH3NC    +    2H2O    =    CH3NH2    +    HCO2H. 

Methyl  Methyl  Formic 

isocyanide.  amine.  acid. 

Isosulphocyanates  or  mustard  oils.  The  difference  in  structure  between 
sulpho-  and  iso-sulphocyanates  is  expressed  in  the  following  formulas : 

R — S — C^N,  sulphocyanate.  E — N=C— S,  isosulphocyanate. 

The  organic  sulphocyanides  are  of  no  importance  here.  The  principal  member 
of  the  mustard  oils  is  allyl-isosulphocyanate,  C3H5NCS,  one  of  the  decomposi- 
tion products  of  myronic  acid. 

Treated  with  water  and  alkali,  mustard  oils  break  down,  thus  : 

C^NCS    +     2H20    =    C3H5NH2    +    H2S    +     CO2. 

This  reaction  is  similar  to  that  which  takes  place  in  case  of  isocyanides.  (See 
above.) 

Myronic  acid,  C10H19NS.2010,  is  found  as  the  potassium  salt,  which  is  known 
as  sinigrin,  in  black  mustard  seed.  When  treated  with  solution  of  myrosin,  a 


BENZENE  SERIES.   AROMATIC  COMPOUNDS.  557 

substance  also  contained  in  mustard  seed  and  acting  as  a  ferment  upon  myronic 
acid  or  its  salts,  potassium  myronate  is  converted  into  dextrose,  allyl  mustard 
oil,  and  potassium  bisulphate. 

KC10H18NS2010  ==  C6H1206  +   C3H5NCS  -f    KHSO4. 

Potassium  Dextrose.      Allyl  mustard       Potassium 

myronate.  oil.  bisulphate. 

Allyl  mustard  oil,  C3H5NCS.  Mustard  oils  are  esters  of  isosulphocyanic 
acid,  HNCS.  Ordinary  mustard  oil,  obtained  from  sinigrin,  as  stated  above, 
contains  the  radical  allyl,  derived  from  the  unsaturated  hydrocarbon  propylene, 
C3H6.  The  univalent  radical  allyl  is  isomeric,  but  not  identical,  with  the  tri- 
valent  radical  glyceryl,  C3H5,  derived  from  propane,  C3H8.  The  difference  may 
be  seen  from  the  structural  formulas : 

— CH2— CH=CH2,  allyl.  — CH2— CH-CH2— ,  glyceryl. 

The  triatomic  alcohol  glycerin,  C3H5(OH)3,  may  be  converted  into  the 
monatomic  allyl  alcohol,  C3H5OH,  by  various  processes.  From  allyl  alcohol 
an  artificial  allyl  mustard  oil  is  manufactured. 

Mustard  oil  is  a  colorless  or  pale  yellow  liquid,  which  has  a  very  pungent 
and  acrid  odor  and  taste.  When  brought  together  with  ammonia,  direct  combi- 
nation takes  place  and  crystals  of  thiosinamine  (allyl-thio-urea),  CS.N2H3.C3H5, 
are  formed  .• 

C3H5NCS  +  NH3  =  CS.N2H3.C3H5. 

Allyl  sulphide,  (C3H5)2S,  is  the  chief  constituent  of  the  oil  of  garlic. 

50.  BENZENE  SERIES.  AROMATIC  COMPOUNDS. 
General  remarks.  It  has  been  stated  before  that  most  organic  com- 
pounds may  be  looked  upon  as  derivatives  of  either  methane,  CH4, 
or  benzene,  C6H6,  these  derivatives  being  often  spoken  of  as  fatty  and 
aromatic  compounds  respectively.  The  term  aromatic  compounds 
was  given  to  these  substances  on  account  of  the  peculiar  and  fragrant 
odor  possessed  by  many,  though  not  by  all  of  them.  Benzene  and 

QUESTIONS. — What  are  the  three  chief  forms  in  which  nitrogen  enters  into 
organic  compounds?  What  are  amines  and  amides;  in  what  respects  do  they 
resemble  ammonia  compounds  ?  What  is  cyanogen,  what  is  dicyanogen,  and 
how  is  the  latter  obtained  ?  How  does  cyanogen  occur  in  nature,  and  which 
non-metallic  elements  does  it  resemble  in  the  constitution  of  various  com- 
pounds ?  Mention  some  reactions  by  which  hydrocyanic  acid  is  formed,  and 
state  the  two  processes  by  which  the  official  diluted  acid  is  obtained.  What 
strength  and  what  properties  has  this  acid  ?  State  the  composition  of  pure 
potassium  cyanide  and  of  the  commercial  article.  How  is  the  latter  made  ? 
Give  reactions  for  hydrocyanic  acid  and  cyanides.  Explain  the  constitution 
and  give  the  composition  of  ferro-  and  ferricyanides.  Give  composition,  mode 
of  manufacture,  and  tests  of  potassium  ferrocyanide.  What  is  red  prussiate 
of  potash,  how  is  it  obtained,  and  by  what  reactions  can  it  be  distinguished 
from  the  yellow  prussiate  ? 


558  CONSIDERATION  OF  CARBON  COMPOUNDS. 

* 

methane  derivatives  differ  considerably  in  many  respects,  and,  as  a 
general  rule,  aromatic  compounds  cannot  be  converted  into  fatty 
compounds,  or  the  latter  into  aromatic  compounds,  without  suffering 
the  most  vital  decomposition  of  the  molecule,  and  in  many  cases  this 
transformation  cannot  be  accomplished  at  all. 

On  the  average,  aromatic  compounds  are  richer  in  carbon  than  fatty 
compounds,  containing  of  this  element  at  least  G  atoms  ;  when  decom- 
posed by  various  methods,  aromatic  compounds,  in  many  cases,  yield 
benzene  as  one  of  the  products  ;  most  aromatic  substances  have  anti- 
septic properties,  and  none  of  them  serves  as  animal  food,  although 
quite  a  number  are  taken  into  the  system  in  small  quantities,  as,  for 
instance,  some  essential  oils,  caffeine,  etc. 

While  some  aromatic  compounds  are  products  of  vegetable  life, 
many  of  them  (like  benzene  itself)  are  obtained  by  destructive  distil- 
lation, and  are,  therefore,  contained  in  coal-tar,  from  which  quite  a 
number  are  separated  by  fractional  distillation. 

Constitution.  —  There  is  not  known  any  benzene  compound  which 
has  less  than  six  atoms  of  carbon.  In  all  of  the  various  decomposi- 
tions and  replacements  which  occur  in  the  formation  of  benzene 
derivatives,  the  six  carbon  atoms  persist,  like  a  unit.  These  condi- 
tions have  led  chemists  to  look  upon  the  six  carbon  atoms  as  being 
joined  together,  forming  a  nucleus  to  which  other  atoms  or  groups 
are  attached,  in  all  of  the  known  aromatic  compounds.  Thus,  in 
benzene,  C6H6,  which  is  the  fundamental  or  mother-substance  of 
these  compounds,  the  six  carbon  atoms  are  joined  to  six  atoms  of 
hydrogen. 

If  benzene  were  of  the  nature  of  a  fatty  compound,  we  should 
expect  to  find  its  structure  correspond  to  a  formula  of  this  kind  : 

H  H 


This  representation  would  indicate  that  benzene  ought  to  behave 
like  a  highly  unsaturated  compound.  Moreover,  we  should  expect 
to  obtain  two  isomeric  compounds  by  replacing  either  a  centrally 
located  hydrogen  atom  or  one  occupying  a  terminal  position. 

As  a  matter  of  fact,  benzene  does  not  behave  like  an  unsaturated 
chain  compound  (although  it  can  be  caused  to  unite  directly  with 
some  elements),  and  by  replacement  of  a  hydrogen  atom  but  one  kind 
of  substitution  product  has  ever  been  obtained.  These  facts  lead  us 
to  believe  that  benzene  is  not  an  unsaturated  chain  compound,  and 


BENZENE  SERIES.     AROMATIC  COMPOUNDS.  559 

» 

that  all  the  hydrogen  atoms  are  equivalent  ;  in  other  words,  the  mole- 
cule C6H6  is  perfectly  symmetrical. 

In  view  of  these  and  many  other  facts  the  conclusion  is  that  the 
six  carbon  atoms  in  benzene  are  united  into  a  cycle  or  ring,  and  that 
each  carbon  atom  is  in  combination  with  one  hydrogen  atom.  This 
view  was  first  put  forth  by  August  KekulS  in  1865.  Graphically 
the  closed  carbon  chain  and  also  benzene  (usually  referred  to  as 
Kekul6's  benzene  hexagon)  are  represented  thus  : 

1  H 

c/2  H\CAC/H 


3  H/  \C^  \ 

i 


This  formula  for  benzene  accounts  for  the  facts  mentioned  above. 
Moreover,  if  two  hydrogen  atoms  are  replaced  by  substituting  atoms 
or  radicals,  three  isomeric  products  are  obtained. 

For  instance,  we  know  three  different  substances  which  have  been 
obtained  by  replacement  of  two  hydrogen  atoms  in  benzene  by  two 
hydroxyl  groups.  This  would  indicate  that  it  makes  a  difference,  as 
far  as  the  properties  of  a  compound  are  concerned,  in  which  relative 
position  the  introduced  radicals  stand  to  one  another,  and  as  a  result 
of  a  great  deal  of  investigation  it  was  found  that  the  following 
formulas  represent  the  three  relative  positions  which  the  two  replac- 
ing groups  may  occupy  in  a  benzene  molecule  : 

OH  OH  OH 

H^        tf^       X)H  Hv        ,C. 


A  >        -* 

\TT  TT/      \C\4> 


H  H  OH 

Ortho-position.  Meta-position.  Para-position. 

1:2.  1:3.  1:4- 

Designating  the  hydrogen  atoms  in  benzene  with  numbers,  thus : 

122456 

C6  H  H  H  H  H  H,  the  above  3  compounds  show  that  in  one  case 
the  hydrogen  atoms  1  and  2,  in  the  second  1  and  3,  in  the  third  1 
and  4  have  been  replaced  by  OH.  The  compounds  formed  in  this 
way  are  distinguished  as  ortho-,  ineta-,  and  para-compounds. 


560 


CONSIDERATION  OF  CARBON  COMPOUNDS. 


The  molecular  formula  of  the  above  three  compounds  is  C6H6O2, 
apparently  indicating  benzene  in  combination  with  two  atoms  of 
oxygen  or  dioxybenzene ;  actually  they  are  dihydroxy  benzene. 

Otfto-dihydroxy  benzene,  C6H4OHOH,  or  C6H4(OH)2  1  :  2,  is  known 

1  3 

as  pyro-catechin,  wefa-dihydroxy  benzene,  C6H4OHOH,  or  C6H4(OH)2 

1  4 

1:3,   as   resorcin,    and   £>ara-dihydroxy    benzene,    C6H4OHOH,  or 
C6H4(OH)2  1  :  4,  as  hydroquinone. 

Benzene  derivatives.  The  analogy  existing  between  methane- 
and  benzene-derivatives  may  be  shown  by  comparing  the  composition 
of  a  few  derivatives  : 


Methane, 

CH4 

Benzene, 

C6H6 

Methyl, 

CH3 

Benzyl, 
Phenyl, 

}C6H5 

Ethane,                        1 
Methyl-methane,       / 

CH3.CH3 

Toluene, 
Methyl-benzene, 

}C6H5.CH3 

Methyl-hydroxide,    \ 
Methyl-alcohol,          / 

CH3OH 

Phenyl-hydroxide, 
Phenol, 

}  C6H5.OH 

/OH 

/OU 

Glycerin, 

C3H5^OH 

Pyrogallol, 

XOH 

SXOH 

Acetic  acid, 

CH3.CO2H 

Benzoic  acid, 

C6H5.CO2H 

Acetic  aldehyde, 

CH3.COH 

Benzoic  aldehyde, 

C6H5.COH 

Ethyl-sulphonic  acid, 

S°2\OH5 

Benzene-sulphonic 
acid, 

SO*\OH5 

Malonic  acid, 

CH  /C°2H 

Phthalic  acid, 

C  H  /C°2H 

Tartaric  acid, 

C2H2/2°2H 

Salicylic  acid, 

c  H  /'OH 

Ethyl  ether, 

g:pH 

Phenyl-ether, 

f  C6H5\0 
lC6H5/° 

Methyl-ethyl  ether,  j 

C2H5V° 

Methyl-phenyl 
ether,  anisol, 

ic6H53)° 

The  following  graphic  formulas  may  serve  to  illustrate  the  consti= 
tution  of  some  aromatic  compounds  : 


OH 

J 


^ 

A 

Benzene,  C«H». 


C02H 

r  I 


H 


i 


H 


Phenol  or  carbolic  acid,        Benzoic  acid,  C6H5.CO9H. 
C6H5.OH. 


BENZENE  SERIES.     AROMATIC  COMPOUNDS. 
NO,  OH 


561 


H  C 

\cx 


II 


H 


H 


Nitro-benzene,  C6H6NOa. 


CH 


Toluene,  methyl-benzene. 
C6H6.CH3. 


CH3 


H 


H 

Xylene,  di-methyl-benzene, 

CH, 


H 


C02H 


XC02H 


A 


H 


Resorcin,  CeH4(OH)2.         Phthulic  acid,  C0H4(CO2H)a. 


H 


OH 

L 


J 


OH 


\OH 


H 


OH 

I 


C02] 


Pyrogallol,  C6H3(OH)3.       Galb'c  acid,  C6H2.CO2H.(OH),. 


OH 
H\A 


OH 


H 


/ 


XCH3 
\H 


H 


H 


/ 


H 


Cresol,  C6H4.CH3.OH. 


CH 


Salicylic  acid,  C6H4.CO2H.OH. 
COH 


\ 


\^f 

i3H7 


H 


Cymene,  methyl-propyl  benzene.    Thymol,  C6H3CH3.C8H7.OH.    Benzaldehyde,  oil  of  bitter 
C6H4  CH3.C3H7.  almond,  C6H6.COH. 

The  preceding  graphic  formulas  show  in  the  first  column  (besides 
nitro-benzene)  a  number  of  hydrocarbons,  in  the  second  column 
phenols,  obtained  by  introducing  hydroxyl  into  the  hydrocarbon 
molecule,  and  in  the  third  column  chiefly  aromatic  acids,  formed  by 
introducing  carboxyl,  CO2H,  or  carboxyl  and  hydroxyl. 

Differences  between  aromatic  and  fatty  compounds.    Substitution  pro- 
ducts with  nitric  acid,  sulphuric  acid,  bromine,  hydrocarbon  radicals,  etc.,  are 
much  more  easily  formed  and  held  much  more  strongly  in  aromatic  compounds 
than  in  fatty  ones.     The  phenols,  which  in  composition  correspond  to  alcohols, 
36 


562  CONSIDERATION  OF  CARBON  COMPOUNDS. 

are  more  acid  than  the  fatty  alcohols ;  aromatic  amines  are  less  alkaline  than 
in  the  fatty  series.     The  phenols  do  not  form  esters  like  the  alcohols. 

Fatty  amines  with  nitrous  acid  yield  alcoholic  compounds ;  aromatic  amines 
behave  quite  differently,  viz.,  a  new  series  of  bodies,  known  as  diazo  compounds, 
is  formed.  Fatty  compounds  are  easily  oxidized,  while  benzene  is  very  stable 
in  the  presence  of  oxidizing  agents. 

Benzene  series  of  hydrocarbons. 

By  replacing  the  hydrogen  atoms  in  benzene  by  methyl,  CH3,  a 
series  of  hydrocarbons  is  formed  having  the  general  composition 
CnH2n_6.  To  this  benzene  series  belong  : 

Benzene      .        .        .  C6H6  B.  P.     80.5°  C. 

Toluene      .        .        .  C7H8         =  C6H5CH3  110 

Xylene        .        .        .  C8H10    -   =  C6H4(CH3)2  141 

Cumene      .         .        .  C9H12     =  C6H8(CH3)8  169 

Tetra-methyl-benzene  C10HU    =  C6H2(CH3)4  190 

Penta-methyl-benzene  C,,H16   =  C6H(CH3)5  231 

Hexa-methyl-benzene  Ci2H18    =  =  C6(CH3)6  264 

The  first  four  members  of  this  series  are  found  in  coal-tar ;  the 
last  three  have  been  obtained  by  synthetical  processes.  While  but 
one  toluene  is  known,  the  higher  members  form  quite  a  number  of 
isomeric  compounds.  Instead  of  adding  two  or  more  methyl  groups 
it  is  possible  to  add  an  ethyl  group,  C2H5,  or  even  higher  homologous 
groups,  thus  producing  a  great  many  isomeric  compounds.  Thus, 
cymene,  C10H14,  found  in  the  oil  of  thyme,  is  not  tetra-methyl-ben- 
zene,  but  para-methyl-iso-propyl-benzene,  C6H4CH3.C3H7.  This  com- 
pound is  of  interest  on  account  of  its  close  relation  to  the  terpenes 
and  camphors,  which  will  be  spoken  of  later. 

Benzene,  C6H6  (Benzol).  When  coal-tar  is  distilled,  products  are 
obtained  which  are  either  lighter  or  heavier  than  water,  and  by  col- 
lecting the  distillate  in  water  a  separation  into  so-called  light  oil 
(floating  on  the  water)  and  heavy  oil  (sinking  beneath  the  water)  is 
accomplished.  Benzene  is  found  in  the  light  oil  and  obtained  from 
it  by  distillation  after  phenol  has  been  removed  by  treatment  with 
caustic  soda  and  some  basic  substances  by  means  of  sulphuric  acid. 
Pure  benzene  may  be  obtained  by  heating  benzoic  acid  with  calcium 
hydroxide  : 

C6H5.CO2H    -f-     Ca(OH)2    ==    CaCO3    +    H2O     +     C6Hfl. 

Experiment  67.  Mix  25  grammes  of  benzoic  acid  with  40  grammes  of  slaked 
lime  and  distil  from  a  dry  flask,  connected  with  a  condenser.  Add  to  the  dis- 
tilled fluid  a  little  calcium  chloride  and  redistil  from  a  small  flask.  The 


BENZENE  SERIES.     AROMATIC  COMPOUNDS.  563 

product  obtained  is  pure  benzene.  Notice  that  it  solidifies  when  placed  in  a 
freezing  mixture  of  ice  and  common  salt.  Observe  the  analogy  between  Ex- 
periments 67  and  51.  In  one  case  a  fatty  acid  is  decomposed  by  an  alkali  with 
liberation  of  methane,  in  the  other  an  aromatic  acid  with  liberation  of  benzene, 
tin-  carbonate  of  the  decomposing  hydroxide  being  formed  in  both  cases. 

Pure  benzene  is  a  colorless,  highly  volatile  liquid,  having  a  peculiar, 
aromatic  odor  and  a  specific  gravity  of  0.884  ;  it  boils  at  80.5°  C. 
(177°  F.)  and  solidifies  at  0°  C.  (32°  F.)  ;  it  is  an  excellent  solvent 
for  fats,  oils,  resins,  and  many  other  organic  substances. 

Nitro-benzene,  C6H3.NO2.  When  benzene  is  treated  with  concen- 
trated nitric  acid,  or  with  a  mixture  of  nitric  and  sulphuric  acids, 
nitro-benzene  is  formed  . 

C6H6    +    HN03    ==    C6H5N02    +    H2O. 

Experiment  68.  Mix  50  c.c.  of  sulphuric  acid  with  25  c.c.  nitric  acid  ;  allow 
to  cool,  place  the  vessel  containing  the  mixture  in  water,  and  add  gradually  5 
c.c.  of  benzene,  waiting  after  the  addition  of  a  few  drops  each  time  until  the 
reaction  is  over.  Shake  well  until  all  benzene  is  dissolved  and  pour  the  liquid 
into  300  c.c.  of  water.  The  yellow  oil  which  sinks  to  the  bottom  is  nitro- 
benzene. It  may  be  purified  by  washing  with  water  and  redistilling,  after 
removal  of  water  and  shaking  with  calcium  chloride. 

Nitro-benzene  is  an  almost  colorless  or  yellowish  oily  liquid,  which 
is  insoluble  in  water,  has  a  specific  gravity  of  1.2,  a  boiling-point  of 
205°  C.  (401°  F.),  a  sweetish  taste,  highly  poisonous  properties,  even 
when  inhaled,  and  an  odor  resembling  that  of  oil  of  bitter  almond, 
for  which  it  is  substituted  under  the  name  of  essence  of  mirbane.  It 
is  manufactured  on  a  large  scale,  and  is  used  chiefly  in  the  preparation 
of  aniline.  Dinitro  benzene  is  also  known. 

Toluene,  C6H5CH3  (Methyl  benzene}.  This  was  first  obtained  by  dry  distilla- 
tion of  balsam  of  tolu,  whence  its  name.  It  occurs  in  coal  tar,  from  which  it 
can  be  separated,  but  may  also  be  made  from  benzene  by  using  a  reaction  gen- 
erally employed  for  the  introduction  of  the  methyl  groups,  thus: 

C6H5Br  +  CH3Br  +   2Na  =  C6H5CH3  +  2NaBr. 

Toluene,  as  well  as  the  other  hydrocarbon  derivatives  of  benzene,  possesses 
properties  of  the  fatty  hydrocarbons  as  well  as  benzene  properties.  This  is 
quite  natural,  because  of  the  fatty  radicals  present  in  the  molecule.  Thus, 
when  oxidized,  toluene  yields  benzoic  acid,  C6H5CO2H,  the  methyl  being 
oxidized  while  the  benzene  ring  is  unchanged. 


Xylenes,  CeH^CHg^  (Dimethyl  benzenes}.  Three  xylenes  are  found  in  coal- 
tar,  and  are  distinguished  as  ortho-,  meta-,  and  para-xylene.  They  can  be 
made  synthetically  from  toluene  in  the  same  manner  as  toluene  is  made  from 
benzene.  When  oxidized  they  yield  ortho-,  meta-,  and  para-phthalic  acids,  of 
the  composition  C6H4(C02H)2. 


564  CONSIDERATION  OF  CARBON  COMPOUNDS. 


Cymene,  C10H14  or  CgH^CH^.CgHy  (para-methyl-isojjroj^-benzene). 
This  hydrocarbon  occurs  in  the  oil  of  thyme  and  in  the  volatile  oils 
of  a  few  other  plants  ;  it  has  also  been  made  synthetically  ;  it  is  a 
liquid  of  a  pleasant  odor,  boiling  at  175°  C.  (347°  F.). 

Cymene  is  of  special  interest,  because  it  is  closely  related  to  the 
terpenes  and  camphors,  from  all  of  which  it  may  be  obtained  by 
comparatively  simple  processes. 


Amino  compounds  of  benzene. 

Aniline,  Phenyl-amine,  C6H5NH2.  The  constitution  of  amines, 
to  which  class  aniline  belongs,  has  been  considered  in  Chapter  49. 
Aniline  is  found  in  coal  tar  and  in  bone-oil;  it  is  manufactured  on 
a  large  scale  by  the  action  of  nascent  hydrogen  upon  nitro-benzene, 
iron  and  hydrochloric  acid  being  generally  used  for  generating  the 
hydrogen. 

Experiment  69.  Dissolve  20  c.c.  of  nitro-benzene  (this  may  be  obtained 
according  to  the  directions  given  in  Experiment  68,  using  larger  quantities  of 
the  material)  in  alcoholic  ammonia  and  pass  through  this  solution  hydrogen 
sulphide  as  long  as  a  precipitate  of  sulphur  is  produced ;  the  reaction  takes 
place  thus : 

C6H5NO2    -f    3H2S    =    C6H5NH2     +     2H2O     +    3S. 

Evaporate  on  a  water-bath  to  expel  ammonium  sulphide  and  alcohol ;  add  to 
the  residue  dilute  hydrochloric  acid,  which  dissolves  the  aniline,  but  leaves  any 
unchanged  nitro-benzene  undissolved.  Separate  the  nitro-benzene  from  the 
aniline  chloride  solution,  evaporate  this  to  dryness,  mix  with  some  lime,  in 
order  to  liberate  the  aniline,  which  may  be  obtained  by  distillation  from  a  dry 
flask. 

Pure  aniline  is  a  colorless,  slightly  alkaline  liquid,  having  a  pecu- 
liar, aromatic  odor,  a  bitter  taste,  and  strongly  poisonous  properties. 
It  boils  at  184.5°  C.  (364°  F.).  Like  all  true  amines,  it  combines 
with  acids  to  form  well-defined  salts. 

Aniline  dyes.  The  crude  benzene  used  in  the  manufacture  of  aniline 
dyes  is  generally  a  mixture  of  benzene,  C6H6,  and  toluene,  C7H8. 
This  mixture  is  first  converted  into  nitro-benzene,  C6H6NO2,  and 
nitro-toluene,  C7H7NO2,  and  then  into  aniline,  C6H5NH2,  and  tolu- 
idine,  C7H7NH2.  When  these  substances  are  treated  with  oxidizing 
agents,  such  as  arsenic  oxide,  hypochlorites,  chromic  or  nitric  acid, 
etc.,  various  substances  are  obtained  which  are  either  themselves  dis- 
tinguished by  beautiful  colors  or  may  be  converted  into  numerous 
derivatives  showing  all  the  various  shades  of  red,  blue,  violet,  green, 
etc. 


BENZENE  SERIES.     AROMATIC  COMPOUNDS.  565 

As  an  instance  of  the  formation  of  an  aniline  dye  may  be  men- 
tioned that  of  roaaniline,  which  takes  place  thus: 

C6H7N     -f     2C7H9N     +     30        :    C20H19N3    +    3H2O. 
Aniline.  Toluidine.  Rosaniline. 

Experiment  70.  To  some  of  the  aniline  obtained  by  performing  Experiment 
69  add  a  little  solution  of  bleaching  powder:  a  beautiful  purple  color  is  ob- 
tained. Treat  another  portion  with  sulphuric  acid  to  which  an  aqueous  solu- 
tion of  potassium  dichromate  has  been  added :  a  blue  color  is  produced.  A 
third  quantity  treat  with  solution  of  cupric  sulphate  and  potassium  chlorate: 
a  dark  color  is  the  result. 

Acetanilide,  Acetanilidum,  C6H5.NH.(CH3CO)  —  134.09,  (Anti- 
febrine,  Phcnylacdamide).  The  term  anilide  is  used  for  derivatives 
of  aniline  obtained  from  this  compound  by  replacement  of  the  am- 
monia hydrogen  (or  amino  hydrogen)  by  acid  radicals.  If  the  radical 
introduced  is  acetyl,  C2H3O,  the  resulting  compound  is  acetanilide, 

C*  TT 

the  constitution  of  which  is  represented  in  the  formula  NH^p6TT5r\ 

It  is  obtained  by  boiling  together  for  one  or  two  days  equal  weights 
of  pure  aniline  and  glacial  acetic  acid,  distilling  and  collecting  the  por- 
tion which  passes  over  at  a  temperature  of  about  295°  C.  (563°  F.). 
The  distillate  solidifies  on  cooling  and  may  be  purified  by  recrystalliza- 
tion  from  solution  in  water.  The  chemical  change  taking  place  is  this  : 

C6H6NH2  +  C2H4O2  =  C6H5.NH.C2H3O  +  H2O. 

Pure  acetanilide  forms  white  odorless  crystals  of  a  silky  lustre  and  a  greasy 
feeling  to  the  touch.  It  fuses  at  113°  C.  (235°  F.)  and  boils  at  295°  C.  (563°  F.) ; 
it  is  but  slightly  soluble  in  cold,  much  more  soluble  in  hot  water,  readily  solu- 
ble in  alcohol  and  ether ;  the  solutions  have  a  neutral  reaction  and  are  not 
colored  by  either  concentrated  sulphuric  acid  or  by  ferric  chloride. 

Analytical  reactions: 

1 .  When  0.1  gramme  of  acetanilide  is  boiled  for  several  minutes  with 
2  c.c.  of  hydrochloric  acid,  and  to  this  solution  are  added  3  c.c.  of  an 
aqueous  solution  of  phenol  (1  in  20)  and  5  c.c.  of  a  filtered,  saturated 
solution  of  bleaching  powder,  a  brownish-red  liquid  is  obtained  which 
turns  deep  blue  upon  supersaturation  with  ammonia  water. 

2.  On  heating  0.1  gramme  of  acetanilide  with  a  few  c.c.  of  concen- 
trated solution  (1  in  4)  of  potassium  hydroxide,  the  odor  of  aniline 
becomes  noticeable ;  on  now  adding  chloroform,  and  again   heating, 
the  disagreeable  odor  of  the  poisonous  phenyl-isocyanide,  C6H5NC,  is 
evolved  (distinction  from  antipyrine). 

3.  A  mixture  of  equal  parts  of  acetanilide  and  sodium   nitrite 


566  CONSIDERATION  OF  CARBON  COMPOUNDS. 

sprinkled  upon  concentrated    sulphuric  acid    produces  a  bright-red 
color. 

Compound  acetanilide  powder,  Pulvis  acetanilidi  compositus,  is 
a  mixture  of  70  parts  of  acetanilide,  10  parts  of  caffeine,  and  20  parts  of  sodium 
bicarbonate.  It  is  one  form  of  the  numerous  headache  powders  in  the  market, 
in  which  acetanilide,  the  cheapest  of  the  common  antipyretics,  is  a  common  con- 
stituent. Sodium  bicarbonate  increases  the  solubility  of  the  acetanilide. 

Methyl  acetanilide  C6H5.N.CH3.C2H30,  (Exalgin],  may  be  made  by  the 
acetylating  of  monomethyl-aniline.  It  occurs  as  a  crystalline  powder  or  in 
large  crystalline  needles  ;  it  is  tasteless  and  almost  insoluble  in  water. 

Sulphanilic  acid,  Amline-para-sulphonic  acid,  C8H4.NH,.S03H.  Obtained 
by  heating  1  part  of  pure  aniline  oil  with  2  parts  of  fuming  sulphuric  acid, 
and  purifying  the  product  by  crystallization. 


C6H5.NH2     +     H2SO,    =    C6H4.NH2.SO3H     +    H2O. 

It  is  a  colorless  crystalline  substance,  soluble  in  182  parts  of  cold  water. 
When  sulphanilic  acid  is  acted  upon  by  nitrous  acid,  it  is  converted  into  diazo- 
benzol-sulphonic  acid,  C6H4N.N.SO3,  which  is  of  interest  because  it  is  used  as  a 
reagent  in  Ehrlich's  diazo-reaction  in  urinary  analysis. 

Diphenyl-amine,  (C6H5)2NH,  is  obtained  by  the  destructive  distillation  of 
triphenyl-rosaniline  (aniline-blue)  as  a  grayish  crystalline  substance,  slightly 
soluble  in  water,  more  soluble  in  acids.  A  0.2  per  cent,  solution  in  diluted 
sulphuric  acid  (forming  diphenylainine  sulphuric  acid)  is  colored  intensely 
blue  by  nitric  acid;  also,  temporarily  by  nitrous  acid  and,  somewhat  less 
intensely,  by  hypochlorous,  bromic,  and  iodic  acids,  and  a  number  of  other 
oxidizing  agents. 


Diamino-benzene,  Meta-phenylene-diamine,  CgH^NHa^,  is  obtained  by 
the  reduction  of  meta-dinitro-benzene  as  a  grayish  crystalline  powder.  It  has 
strongly  basic  properties,  is  somewhat  soluble  in  water,  readily  soluble  in  alco- 
hol or  ether.  It  is  a  valuable  reagent  for  nitrites,  as  it  forms,  with  even  traces 
of  nitrous  acid,  an  intense  yellow  color. 

Methylthionine  hydro  chloride,  Methylthioninae  hydrochlori- 
dum,  C16H18N3SC1  =  317.36  (Methylene  blue).  This  is  a  very  complex 
dye  obtained  by  treating  dimethyl-paraphenylene-diamine,  C6H4.- 
(NH2)N(CH3)2,  in  hydrochloric  acid  solution  with  hydrogen  sulphide 
and  subsequently  with  ferric  chloride.  It  occurs  as  a  dark-green 
powder  or  in  prismatic  crystals  having  a  bronze-like  lustre,  readily 
soluble  in  water  and  somewhat  less  so  in  alcohol,  giving  solutions  of 
a  deep-blue  color.  Alkalies  change  the  color  of  the  aqueous  solution 
to  a  purplish  shade,  and  in  excess  cause  a  precipitate  of  a  dull-violet 
color.  It  is  incompatible  with  potassium  iodide,  and  reducing  agents 
decolorize  it. 


BENZENE  SERIES.     AROMATIC  COMPOUNDS.  567 

Methylene-blue  should  not  be  confounded  with  the  commercial  article,  which 
is  often  the  zinc  chloride  double  salt  of  methylthionine,  is  employed  as  a  dye  or 
stain,  and  is  unfit  for  medicinal  purposes.  The  presence  of  zinc  can  be  told  by 
incinerating  2  grammes  of  the  substance  and  testing  the  ash  in  the  usual  way 
for  zinc.  Methylene-blue  should  also  not  be  confounded  with  methyl  blue, 
which  is  the  sodium  salt  of  triphenyl-pararosaniline-trisulphonic  acid.  A  solu- 
tion of  the  latter  with  alkalies  changes  to  reddish-brown, 

Methylene  azure,  C18H18N3S03C1,  is  derived  from  methylene-blue  by  the  ad- 
dition of  oxygen.  It  is  present  in  "ripened"  methylene-blue  and  almost 
always  in  even  the  best  specimens  of  the  medicinal  article.  It  may  be  detected 
by  adding  ammonia  to  a  solution  of  methylene-blue  and  then  shaking  with 
ether ;  the  methylene-azure  passes  into  the  ether,  which  is  colored  red. 

Diazo  compounds  of  benzene. 

When  fatty  amines  are  treated  with  nitrous  acid  the  ammo  group 
is  replaced  by  hydroxyl,  thus : 

C2H5.NH2    +    HONO    =    C2H5OH    -f    2N    +    H2O. 

When,  however,  an  aromatic  amine  is  treated  with  nitrous  acid, 
in  acid  solution,  a  new  class  of  compounds  is  formed,  known  as 
diazo-compounds,  thus : 

C6H5.NH2HC1   +   HONO   =   C6H5.Na.Cl  -f-   2H20. 

Aniline  Diazo-benzene 

hydrochloride.  chloride. 

The  characteristic  diazo  grouping  is  expressed  thus  :  R — N2 — ,  and 
this  group  combines  with  acid  residues  to  form  diazo-salts,  such  as 
diazo-benzene  nitrate,  C6H5.N2.NO3,  sulphate,  C6H6.N2.SO4H,  etc. 

The  diazo-compounds  are  colorless,  crystalline,  unstable,  and  even  explosive 
substances ;  soluble  in  water,  insoluble  in  ether.  They  are  of  great  scientific 
and  technical  importance,  as  they  form  the  starting-point  for  a  large  class 
of  dyes.  Diazo-compounds  are  decomposed  by  water,  either  in  the  cold  or  upon 
heating,  the  N2  group  being  usually  replaced  by  the  (OH)  group,  thus : 

C6H5.N2.NO3    +    H2O    =    C6H5OH    -f    N2    +    HNO3. 

It  is  thus  possible  to  introduce  hydroxyl  into  the  benzene  nucleus  through  the 
medium  of  nitre-compounds,  and  obtain  substances  belonging  to  the  class  of 
phenols. 

Diazo-compounds  have  a  marked  tendency  to  react  with  other  substances, 
especially  amino-compounds  and  phenols,  to  form  a  class  known  as  azo-com- 
pounds, which  are  characterized  by  having  the  group  — N  =  N —  in  combina- 
tion with  two  residues.  Azobenzene,  C6H5 — N  =  N — C6H5,  is  the  mother- 
substance  of  all  azo-compounds,  most  of  which  are  highly  colored,  and  many 
are  used  as  dyes.  The  formation  of  colored  azo-compounds  is  involved  in  the 
test  for  nitrites  in  drinking-water  by  meta-phenylene-diamine  (see  page  432), 
which  gives  triamino-azobenzene,  NH2.C6H4— N  =  N— C6H3(NH2)2,  a  dye 
which  has  been  on  the  market  since  1866  and  known  as  Bismark  brown ;  also 


568  CONSIDERATION  OF  CARBON  COMPOUNDS. 

the  test  in  which  sulphanilic  acid  and  alpha-naphthylamine  are  used.  In 
Ehrlich's  Diazo  Reaction  for  typhoid  fever,  it  is  believed  that  some  unknown 
phenolic  or  amino  compound  in  the  urine  unites  with  the  diazo-sulphanilic 
acid  reagent,  and  forms  an  azo-dye.  Some  of  the  indicators  used  in  volumetric 
analysis  are  azo-dyes,  for  example,  methyl-orange  (see  page  410).  Dimethyl- 
amino-azobenzol,  C6H5 — N  =  N— C6H4.N(CH3)2,  is  used  to  detect  hydrochloric 
acid  in  stomach  contents. 

Phenyl  hydrazine,  C6H5.NH.NH2.  When  diazo-compounds  are  reduced, 
they  yield  derivatives  of  the  mother-substance,  H2N — NH2,  known  as  hydra- 
zine, or  diamine.  Thus,  diazo-benzene  yields  phenyl  hydrazine.  It  is  a 
strongly  basic  substance  and  unites  readily  with  acids  to  form  salts ;  it  is  a 
colorless  crystalline  substance,  sparingly  soluble  in  water,  but  soluble  in  acids. 
Phenylhydrazine  is  of  interest  because  it  is  used  in  the  manufacture  of  anti- 
pyrine,  and  as  a  valuable  reagent  for  the  detection  of  aldehydes  and  sugars. 
It  combines  with  both  classes  of  compounds,  forming  with  aldehydes  bodies 
known  as  hydrazones,  with  sugars,  osazones.  Most  of  these  compounds  are  solid 
and  crystalline;  the  crystalline  structure  often  serves  for  identification. 

Arsenic  and  phosphorus  derivatives.  A  number  of  compounds  of  aro- 
matic hydrocarbons  containing  arsenic  and  phosphorus,  and  having  compo- 
sitions similar  to  nitro-,  azo-,  and  amino-compounds,  are  known.  The  simi- 
larities are  shown  in  the  following  table : 


C6H5.NO2 

Nitrobenzene. 

C6H5.N,C6H5 

Azobenzene. 

C6H5.NH2 

Phenylamine. 

C6HVP02 
Phosphinobenzene. 

C6K5.P2.C6H5 

Phosphobenzene. 

C6H5.PH2 

Phenylphosphine. 

C6H5AsO2 

Arsinobenzene. 

C6H5.As2.C6H5 

Arsenobenzene. 

Arsenobenzene,  C6H5.As  :  As.C6H5,  is  obtained  by  the  reduction  of  phenyl- 
arsine  oxide,  C6H5.AsO,  by  phosphorous  acid,  as  yellow  needles.  By  oxidation 
it  is  converted  into  phenylarsonic  acid,  C6H5.AsO(OH)2. 

Sodium  para-aminophenyl  arsonate,  NH2.C6H4.AsO(OH).ONa.3H2O  (sodium 
arsanilate,  sodium  aniline  arsonate,  atoxyl),  is  a  white,  odorless,  crystalline  salt, 
soluble  in  about  6  parts  of  water,  and  having  a  faint  salty  taste.  The  aqueous 
solution  on  standing  assumes  a  yellowish  tint.  It  is  used  in  sleeping  sickness 
(trypanosomiasis),  syphilis,  malaria,  etc.  It  should  be  given  hypodermically, 
and  not  by  the  mouth.  Atoxyl  is  made  by  heating  aniline  arsenate  to  about 
200°  C.  for  several  hours,  when  a  reaction  takes  place  analogous  to  that  by 
which  para-amino-benzene  sulphonic  acid  (sulphanilic  acid)  is  formed  by  heat- 
ing aniline  sulphate  : 

C6H5NH2.(HO)3AsO        =        NH2.C6H4.AsO(OH)2        +        H2O 
Aniline  arsenate.  Para-aminophenyl  arsonic  acid. 

The  sodium  salt  of  this  acid  is  atoxyl. 

IKoxydiaminoarsenobenzene,     ^)^C6H8.Afl  :  As.C6H3<^^^     ffi.        The 

dihydrochloride  ("bichloride,"  as  it  is  called  in  the  market)  of  this  diamine 
compound  was  prepared  by  Ehrlich  and  Bertheim,  and  was  the  606th  com- 
pound made  in  a  search  for  a  specific  remedy  for  germ  diseases.  It  is  known 
as  "  606,"  or  salvarsan.  The  arsenic  occupies  the  para  position  in  the  benzene 


BENZENE  SERIES.     AROMATIC  COMPOUNDS.  569 

nucleus.  This  substance  has  basic  properties  due  to  the  NH2  groups,  and 
therefore  unites  with  acids ;  it  also  has  acid  properties  due  to  the  (OH)  groups, 
and  forms  salts  with  alkalies  just  as  phenol  does. 

Salvarsan  is  a  lemon-yellow  powder,  which  comes  in  sealed  tubes.  It  is 
soluble  in  water  with  a  decided  acid  reaction,  due  to  hydrolysis  and  liberation 
of  hydrochloric  acid.  The  sodium  salt  gives  an  alkaline  reaction  in  solution, 
due  to  hydrolysis  and  liberation  of  sodium  hydroxide.  The  free  base  is  insolu- 
ble in  water  and  is  precipitated  by  the  cautious  addition  of  alkali  to  the  solu- 
tion of  the  hydrochloride,  or  of  acid  to  the  solution  of  the  sodium  compound. 
For  injections,  either  a  suspension  of  the  free  base  or  a  solution  of  the  mono- 
or  di-sodium  salt  is  prepared  from  salvarsan. 

Hydroxyl  derivatives  of  the  benzene   series. 

Phenols  are  hydroxyl  derivatives  of  benzene.  The  name  is  a  gen- 
eral one  for  all  such  compounds.  Phenols  are  allied  to  the  tertiary 
fatty  alcohols,  as  they  contain  the  characteristic  grouping  =  C  — OH. 
According  to  the  number  of  hydrogen  atoms  replaced  by  hydroxyl, 
we  find  mono-,  di-,  and  tri-hydroxy  phenols,  corresponding  to  the 
similarly  constituted  alcohols.  Phenols  differ  from  common  alcohols 
in  not  yielding  aldehydes  or  acids  by  oxidation. 

Phenols  are  either  liquid  or  solid,  and  often  have  a  peculiar  odor.  Most  of 
them  can  be  distilled  without  decomposition,  and  are  readily  soluble  in  alcohol 
and  ether  ;  some  are  readily  soluble  in  water.  Many  are  antiseptic,  for  example, 
phenol,  cresol,  resorcin,  thymol,  etc.  Many  individual  phenols  are  found  in  the 
vegetable  and  animal  kingdoms.  Destructive  distillation  of  complex  carbon 
compounds  usually  results  in  the  formation  of  phenols  among  the  products; 
thus,  wood-tar  and  coal-tar  are  rich  in  phenols. 

Phenols  act  like  weak  acids,  forming  salts  with  caustic  alkalies,  which  are 
soluble  in  water  and  far  more  stable  than  the  alcoholates.  But  they  do  not 
decompose  carbonates. 

Phenols  can  be  obtained  readily  by  first  preparing  sulphonic  acids,  and  fusing 
the  alkali  salts  of  these  with  caustic  soda  or  potash.  The  actions  are  shown  in 
the  following  equations,  which  relate  to  synthetic  phenol : 

C6H6    +    H2S04  C6H5S03H    +     H20. 

Benzene 
eulphonic  acid. 

C6H5SO3Na    +     NaOH  C6H5OH.     +     Na2SO3. 

Phenol. 

The  phenol  is  liberated  from  its  alkali  salt  by  an  acid,  and  is  purified  by 
further  appropriate  treatment. 

Phenol,  C6H5OH  =  93.34  ( Carbolic  acid,  Phenyl  hydroxide).  Crude 
carbolic  acid  is  a  liquid  obtained  during  the  distillation  of  coal-tar 
between  the  temperatures  of  170°-190°  C.  (338°-374°  F.),  and  con- 
taining chiefly  phenol,  besides  cresol,  C7H7OH,  and  other  substances. 


570  CONSIDERATION  OF  CARBON  COMPOUNDS. 

It  is  a  reddish-brown  liquid  of  a  strongly  empyreumatic  and  dis- 
agreeable odor. 

By  fractional  distillation  of  the  crude  carbolic  acid,  the  pure  acid 
is  obtained,  which  forms  colorless,  interlaced,  needle-shaped  crystals, 
sometimes  acquiring  a  pinkish  tint ;  it  has  a  characteristic,  slightly 
aromatic  odor,  is  deliquescent  in  moist  air,  soluble  in  from  15  to  20 
parts  of  water,  and  very  soluble  in  alcohol,  ether,  chloroform,  glycerin, 
fat  and  volatile  oils,  etc. ;  it  has,  when  diluted,  a  sweetish  and  after- 
ward burning,  caustic  taste;  it  produces  a  benumbing  and  caustic 
effect,  and  even  blisters  on  the  skin ;  it  is  strongly  poisonous,  and  a 
powerful  disinfectant,  preventing  fermentation  and  putrefaction  to  a 
marked  degree  ;  fusing  point  of  the  official  article  not  less  than  40°  C. 
(104°  F.);  boiling  point  188°  C.  (370°  F.). 

Phenol,  though  generally  called  carbolic  acid,  has  a  neutral  or  but 
faintly  acid  reaction,  and  the  constitution  of  a  tertiary  alcohol,  but  it 
readily  combines  with  strong  bases,  for  instance,  with  sodium  hy- 
droxide, forming  sodium  phenoxide  or  sodium  phenolate  : 

C6H6OH        -f        NaOH        =        C6H6OXa        +        HaO. 

Phenol  obtained  by  synthetical  processes  is  now  sold  in  a  state  of 
great  purity ;  it  has  comparatively  little  odor. 

Phenol  is  readily  liquefied  by  a  small  amount  of  water  and  is 
usually  dispensed  in  this  form.  The  Liquefied  phenol  of  the  U.  S.  P. 
contains  about  13.6  per  cent,  of  water. 

Phenol  often  becomes  colored  when  exposed  to  air  and  light.  This  is  due 
to  oxidation.  When  pure  it  remains  colorless  even  in  sunlight  if  it  is  kept  in 
an  atmosphere  of  inert  gases,  as  hydrogen,  nitrogen,  or  carbon  dioxide.  The 
rate  of  oxidation  varies  with  the  temperature,  being  rapid  at  the  boiling-point 
of  phenol.  The  products  of  oxidation  are  quinol,  quinone,  and  catechol,  and 
the  principal  colored  compounds  are  probably  quinone  condensation  products. 
The  formation  of  the  intensely  red  substance  called  phenoquinone  is  probable. 
Glass  which  most  completely  absorbs  ultra-violet  light  retards  the  action  of 
oxygen  on  phenol  in  the  greatest  degree. 

Phenol  or  carbolic  acid  coefficient  (Rideal-  Walker  coefficient}.  Bacte- 
riological standardization  of  disinfectants  was  proposed  in  1896  by  C.  G.  Moor. 
In  1903  Samuel  Rideal  and  Ainslie  Walker  developed  the  method  now  in  use, 
which,  with  later  improvements,  is  the  best  available  in  spite  of  some  defects. 
In  this  method  carbolic  acid  is  taken  as  the  standard  of  comparison  for  other 
disinfectants.  The  phenol  or  carbolic  acid  coefficient  is  the  ratio  of  the  strength 
in  which  a  given  disinfectant  kills  a  given  organism  to  that  of  carbolic  acid 
which  effects  the  same  sterilization  in  the  same  time.  The  colon  or  typhoid 
bacillus  is  employed  in  the  experiments  of  comparison. 

The  meaning  of  the  coefficient  will  appear  clear  from  the  following  exam- 
ple, which  refers  to  a  culture  of  bacillus  pestis.  A  1  in  40  formaldehyde  solu- 
tion was  equivalent  to  a  1  in  110  solution  of  carbolic  acid,  both  sterilizing  in 


BENZENE  SERIES.     AROMATIC  COMPOUNDS.  571 

ten  minutes,  but  not  in  seven  and  a  half  minutes.     Hence,  carbolic  acid  coeffi- 
cient of  the  formaldehyde  in  this  instance  was  ^,  or  0.36. 

The  laws  of  some  states  require  the  labels  of  substances  sold  as  disinfectants 
to  state  the  carbolic  acid  coefficient.  The  following  table  shows  the  coefficients 
and  the  relative  money  values  of  various  disinfectants  in  the  market: 

Carbol'         '   C°St  °f  the  Quantity  of  dls' 
Disinfectant.  acid  "  Infectant  equivalent  to  1 

coefficient  EngUsh  gttll°n  °f  98  per 

cent,  carbolic  acid. 

Carbolic  acid,  98  per  cent 1.00  $    0.25 

Chinosol  .               0.30  127.87 

Condy's  fluid 0.90  2.00 

Cyllin  (a  cresol) 11.00  0.08 

Formaldehyde 0.30  4.40 

Izal 8.00  0.12 

Listerine 0.03  324.62 

Lysoform 0.10  36.49 

Lysol 2.50  0.76 

Pearson's  antiseptic 1.40  0.42 

Sanitas 0.02  42.56 

The  coefficients  of  some  other  disinfectants  are :  sulphonaphthol,  2.2 ;  zeno- 
leum,  2.49 ;  kreso,  2.5 ;  chloronaphtholeum,  5.4 ;  hyco,  19 ;  Platt's  chlorides,  3. 

Antidotes.  Alcohol  is  the  best  antidote ;  it  prevents  the  corrosive  action  of 
phenol.  But  the  stomach  should  be  at  once  emptied  and  washed  out,  else  the 
phenol  will  be  absorbed  and  then  alcohol  would  prove  worse  than  no  antidote. 
Soluble  sulphates  have  been  recommended  on  the  supposition  that  harmless 
phenolsulphonates  are  formed,  but  recent  experimenters  have  asserted  that 
they  are  useless  as  an  antidote.  Hot  applications  to  the  extremities,  hypo- 
dermic injection  of  cardiac  and  respiratory  stimulants,  intravenous  injection  of 
normal  saline  solution,  and  morphine  to  relieve  pain,  are  valuable  aids  in  phenol 
poisoning. 

Tests  for  phenol. 
(Use  an  aqueous  solution.) 

1.  It  coagulates  albumin  and  collodion. 

2.  It  colors  solutions  of  neutral  ferric  chloride  intensely  and  per- 
manently violet-blue. 

3.  Bromine  water,  added  in  excess,  produces,  even  in  dilute  solu- 
tions, a  white  precipitate  of  tri-brom-phenol,  C6H2Br3OH,  which  has 
been  used  medicinally  under  the  name  of  Bromol. 

4.  Millon's  reagent  (see  Index),  heated  to  boiling  with  phenol  solu- 
tion, gives  an  intense  red  color  on  addition  of  a  few  drops  of  nitric 
acid. 

5.  On  heating  with  nitric  acid  it  turns  yellow,  nitre-phenols  being 
formed. 


572  CONSIDERATION  OF  CARBON  COMPOUNDS. 

Bismuth  tribrom-phenolate,  Bi2O2.OH.(OC6H2Br3)  (Xeroform},is  a  fine 
yellow,  nearly  odorless  and  tasteless  powder,  insoluble  in  water  or  alcohol,  but 
soluble  in  2  per  cent,  hydrochloric  acid  in  the  proportion  of  30  : 100.  It  is  incom- 
patible with  alkaline  media  and  should  not  be  heated  above  120°  C.  It  is  a  non- 
irritant  and  non-toxic  antiseptic,  recommended  as  a  substitute  for  iodoform. 

Nitro-plienols.  Mono-,  di-,  and  trinitro-phenols  are  known.  Mononitro- 
phenol  is  formed  by  the  action  of  dilute  nitric  acid  on  phenol ;  the  di-  and  tri- 
nitro-  derivatives  are  formed  by  further  nitration.  Mononitro-phenol  is  of  in- 
terest also  because  it  is  used  in  the  manufacture  of  acetphenetidiu. 

Acetphenetidin,  Acetphenetidinum,  C6H4.O(C2H5).NH(C2H3O)  = 
177.79  (Phenacetin).  When  mononitro-phenol,  C6H4.NO2.OH,  is 
treated  with  reducing  agents,  the  oxygen  of  NO2  is  replaced  by  hy- 
drogen, and  amino-phenol,  C6H4.OH.NH2,  is  formed.  The  methyl 
ether  of  this  compound,  C6H4.O(CH3).NH2,  is  known  as  anisidin, 
and  the  ethyl  ether,  C6H4.O(C2H5).NH2,  as  phenetidin.  By  the 
action  of  glacial  acetic  acid  upon  para-phenetidin,  one  hydrogen  atom 
in  NH2  is  replaced  by  acetyl,  C2H3O,  when  para-acetphenetidin  is 
formed.  The  compound  is  used  as  an  antipyretic  under  the  name 
of  phenacetin. 

It  is  a  colorless,  odorless,  tasteless  powder,  sparingly  soluble  in 
water,  readily  soluble  in  alcohol;  it  fuses  at  135°  C.  (275°  F.). 
Fresh  chlorine  water  colors  a  hot  aqueous  solution  first  violet,  then 
ruby-red.  The  same  color  is  obtained  by  boiling  0.1  gramme  of 
phenacetin  with  1  c.c.  of  hydrochloric  acid  for  one  minute,  diluting 
with  10  c.c.  of  water,  filtering  when  cold,  and  adding  3  drops  of 
solution  of  chromic  acid. 

Acetphenetidin  is  the  best-known  one  of  a  large  number  of  derivatives  of 
para-aminophenol,  known  as  the  phenetidin  series.  These  derivatives,  as  well 
an  acetphenetidin  itself,  are  contained  in  many  migraine  and  headache  powders. 
Lactophenin  is  lactyl-para-phenetidin,  C2H5OC6H4NH.COCH(OH)CH3,  a  diffi- 
cultly soluble  white  powder.  Sal-ophen,  saliphen,  phenocoll,  salocoll,  etc.,  are 
similar  derivatives. 

Trinitro-phenol,  C6H2(NO,)3OH  (Picric  acid,  Carbazotic  acid). 
This  substance  is  formed  by  the  action  of  nitric  acid  on  various  mat- 
ters (silk,  wool,  indigo,  Peruvian  balsam,  etc.),  and  is  manufactured 
on  a  large  scale  by  slowly  dropping  phenol  into  fuming  nitric  acid. 
Picric  acid  forms  yellow  crystals  which  are  sparingly  soluble  in 
water ;  it  has  a  very  bitter  taste,  strongly  poisonous  properties,  and 
is  used  as  a  yellow  dye  for  silk  and  wool  and  as  a  reagent  for  albumin. 
While  phenol  has  but  slight  acid  properties,  picric  acid  behaves  like 


BENZENE  SERIES.     AROMATIC  COMPOUNDS.  573 

a  strong  acid,  forming  salts  known  as  picratcs,  most  of  which  an- 
explosives. 

Phenolsulphonic  acid,  C6H4(OH)SO3H  (Sulphocarbolic  acid). 
There  are  three  varieties  of  this  acid,  namely,  ortho,  meta,  and  para. 
The  ortho  and  para  acid  are  most  easily  obtained.  When  pure  phenol 
is  mixed  with  an  equal  weight  of  sulphuric  acid  in  the  cold,  only  the 
ortho  acid  is  formed  : 

C6H5OH     +     H2S04       :    C6H4(OH)S03H    +    H2O. 

At  100°  C.  (212°  F.)  only  the  para  acid  results.  Both  varieties  form 
clear  solutions  with  water,  but  differ  from  each  other  in  the  character 
of  their  salts,  both  as  regards  solubility  and  form  of  the  crystals. 
They  are  monobasic  acids. 

Ortho-phenohulphonic  acid  (Sozolic  acid,  Aseptol)  occurs  on  the 
market  as  a  33  per  cent,  solution.  It  is  a  syrupy  liquid,  having  a 
reddish  color  and  a  feeble  odor.  It  is  used  as  an  antiseptic. 

Sodium  phenolsulphonate,  Sodii  phenolsulphonas  (Sodium  sulpho- 
carbolate),  C6H4(OH)SO3Na  -f  2H2O,  and  Zinc  phenolsulphonate,  Zinci 
phenolsulphonas  (Zinc  sulphocarbolate),  (C6H4(OH)SO3)2Zn  -f-  8H2O, 
are  official  salts  of  para-phenolsulphonic  acid.  They  are  obtained  by 
precipitating  a  solution  of  barium  para-phenolsulphonate  by  sodium 
carbonate  and  zinc  sulphate  respectively,  filtering  off  the  precipitate 
of  barium  carbonate  or  sulphate,  and  evaporating  the  filtrate  to  crys- 
tallization. Both  salts  are  readily  soluble  and  have  antiseptic  and 
astringent  properties. 

Sulphonic  acid  has  been  spoken  of  before,  when  it  was  shown  that  inercap- 
tans  are  converted  into  compounds  termed  sulphonic  acids.  These  acids  may 
be  looked  upon  as  derivatives  of  sulphurous  acid,  obtained  from  it  by  replace- 
ment of  hydrogen  by  radicals.  The  relation  existing  between  carbonic  and 
sulphonic  acids  may  be  represented  by  the  following  formulas  : 

Carbonic  acid,  c°CoH  Sulphuric  acid,  SO2\OH 

Formic  acid,  CO\QH  Sulphurous  acid,  SO*\OH 

Acetic  acid,  CO\OH3  Methyl  -sulphonic  acid, 

Any  compound          CO^w  Anv  sulphonic  acid, 

carbonic  acid, 


According  to  this  view,  phenolsulphonic  acid  is  represented  by  the  formula, 

so  /  Q>H4OH 
5Ua\OH 


Ichthyol,  Sodium  ichthyo-sulphonate,  C.^H^Na-Pe.    Ichthyol  is  the  sodium  or 
ammonium  salt  of  a  complex  sulphonic  acid,  obtained  by  the  dry  distillation 


574  CONSIDERATION  OF  CARBON  COMPOUNDS. 

of  a  bituminous  mineral  found  in  Tyrol.    It  is  a  brown,  tar-like  liquid,  having 
a  disagreeable  odor. 

Cresol,  C7H7OH==1O7.25.  The  official  cresol  is  a  mixture  of  the 
three  isomeric  cresols,  (CCH4.CH3.OH),  or  hydroxyl  derivatives  of 
toluene,  the  ortho-,  para-,  and  meta-cresol.  The  cresols  bear  the  same 
relation  to  toluene  that  phenol  bears  to  benzene,  and  they  resemble 
phenol  very  closely  in  their  properties.  Cresol  is  a  colorless  or  straw- 
colored  refractive  liquid  having  a  phenol-like  odor.  It  is  soluble  in 
60  parts  of  water,  miscible  with  alcohol,  ether,  and  glycerin  in  all 
proportions.  It  boils  at  about  200°  C.  (392°  F.). 

Cresol  is  slightly  soluble  in  water,  hence  it  is  often  used  in  the  form  of  emul- 
sions, or  dissolved  with  the  aid  of  salts  or  of  soap.  Compound  solution  of  cresol, 
Liquor  cresolis  compositus,  is  a  linseed-oil-soap  solution  of  cresol,  of  50  per  cent, 
strength.  It  is  of  much  more  definite  composition  than  many  commercial  prep- 
arations of  similar  nature.  Lysol  is  about  the  same  as  the  official  solution. 
The  mixtures  known  as  creolins  usually  contain  impure  cresol  dissolved  with 
the  aid  of  rosin  soap.  They  usually  form  emulsions  when  diluted  with  water. 
Solveol  and  solutol  are  solutions  of  cresol  made  with  the  aid  of  salts.  Tri-cresol 
(enterot)  is  said  to  contain  35  per  cent,  of  ortho-cresol,  40  per  cent,  of  meta-cresol, 
and  25  per  cent,  of  para-cresol,  and  is  soluble  to  the  extent  of  2.2  to  2.55  per 
cent,  in  water.  A  vast  number  of  other  similar  solutions  are  on  the  market.  It 
is  generally  held  that  cresol  is  more  toxic  to  bacteria  than  phenol  is.  Losophan 
and  europhen  are  iodine  compounds  of  cresol. 

Creosote,  Creosotum.  Two  different  preparations  of  this  name 
are  sold  in  the  market.  One  is  coal-tar  creosote  and  is  chiefly  an 
impure  carbolic  acid.  The  official  creosote  is  a  liquid  product  of  the 
distillation  of  wood-tar,  especially  of  beechwood-tar,  which  contains 
sometimes  as  much  as  25  per  cent,  of  creosote ;  it  resembles  carbolic 
acid  in  many  respects,  especially  in  its  antiseptic  properties  and  its 
action  on  the  skin.  It  is  a  mixture  of  substances,  but  consists  chiefly 
of  guaiacol,  C6H4.OCH3.OH,  and  creosol,  C6H3.CH3.OCH3.OH. 

From  carbolic  acid  beechwood  creosote  may  be  distinguished  by 
requiring  as  much  as  150  parts  of  water  for  solution;  by  being 
miscible  with  the  official  collodium  in  equal  volumes  without  form- 
ing a  coagulum  ;  by  not  being  solidified  on  cooling ;  by  not  coloring 
ferric  chloride  permanently ;  and  by  its  boiling-point,  which  rises 
from  205°  to  215°  C.  (401°  to  419°  F.). 

Creosote  carbonate  (Creosotal]  is  a  mixture  of  carbonic  acid  esters,  anal- 
ogous to  guaiacol  carbonate,  prepared  from  creosote  by  passing  a  current  of 
carbonyl  chloride  into  a  solution  of  creosote  in  sodium  hydroxide.  It  is  a  yel- 
lowish, thick,  clear,  and  transparent  liquid,  odorless,  and  has  a  bland  oily  taste. 


BENZENE  SERIES.     AROMATIC  COMPOUNDS.  575 

It  is  insoluble  in  water,  but  soluble  in  alcohol  and  in  fixed  oils.   It  is  non-toxic 
and  non-irritant  and  is  used  as  a  substitute  for  creosote. 

Guaiacol,  C6H4.OH.OCH;{  =  123.13,  found  in  beechwood  creosote  to  the 
extent  of  from  60  to  90  per  cent.,  is  a  derivative  of  the  diatomic  phenol  catechol 
(pyrocatechin),  C6H4(OH)2,  obtained  from  it  by  replacing  a  hydroxyl  hydrogen 
atom  by  methyl,  CH3.  Guaiacol  is  consequently  monomethyl  catechol.  It  is 
a  colorless,  crystalline  solid,  melting  at  28.5°  C.  (83.5°  F.),  or  a  colorless  re- 
fractive liquid,  boiling  at  205°  C.  (401°  F.),  and  possessing  a  strong  aromatic 
odor.  It  is  difficultly  soluble  in  water,  easily  soluble  in  alcohol  and  ether.  In 
alcoholic  solution  ferric  chloride  produces  an  immediate  blue  color,  changing 
to  emerald  green,  later  to  yellowish.  It  is  obtained  either  synthetically  or 
from  creosote. 

Veratrol,  C6H4(OCH3)2,  the  dimethyl  ether  of  catechol,  is  a  colorless, 
aromatic,  oily  liquid,  having  the  same  boiling-point  as  guaiacol. 

A  number  of  derivatives  of  guaiacol  are  in  the  market,  being  chiefly  com- 
pounds with  acid  radicals,  such  as  the  camphorate  (guaiacamphol),  carbonate, 
benzoate  (benzosol],  cinnamate  (styracot),  phosphate,  phosphite,  salicylate 
(guaiacol-salol),  valerate  (geosote),  etc.,  one  of  which  is  official,  namely, 

Guaiacol  carbonate,  Guaiacolis  carbonas,  (C7H7O),.CO3,  is  prepared  by  satu- 
rating guaiacol  with  sodium  hydroxide,  and  treating  this  compound  with  car- 
bonyl  chloride,  COC12.  It  is  a  white  crystalline  powder,  insoluble  in  water, 
sparingly  soluble  in  alcohol,  soluble  in  ether  and  chloroform. 

Creosol,  C6H3.CH3.OH.OCH3,  the  second  constituent  of  creosote,  is  the  next 
homologue  to  guaiacol — i.  e.,  the  methyl-ether  of  dioxytoluene. 

Eugenol,  C6H3(OH)(OCH3).C3H5.  4  :  3  :  1  =  162.86,  is  an  unsaturated 
aromatic  phenol  obtained  from  oil  of  cloves  and  other  sources.  It  is  a  color- 
less>  or  a  pale  yellow  liquid,  having  a  strongly  aromatic  odor  of  cloves. 

Safrol,  Safrolum,  C6H3.C3H5.OOCH2,  1:3:4  =  180.86  (Shikimol,  Allyl- 
pyrocatcchol  methylene  ether),  is  found  in  oil  of  sassafras,  oil  of  camphor,  and 
other  volatile  oils.  It  is  a  colorless  liquid  with  a  sassafras-like  odor. 

Thymol,  C10HUO  or  CGH3.CH3.C3H7.OH  —  149.66  (Mdhyl-isopro- 
pylphenol).  Thymol  is  found  in  small  quantities  as  a  constituent  of 
the  volatile  oils  of  wild  thyme,  horse-mint,  and  a  few  other  plants. 

Thymol  crystallizes  in  large  translucent  plates,  has  a  mild  odor,  a  warm, 
pungent  taste,  melts  at  50°  C.  (122°  F.)  and  boils  at  230°  C.  (446°  F.,  It  is  now 
largely  used  as  an  excellent  and  very  valuable  antiseptic,  preference  being 
given  to  it  on  account  of  its  comparative  harmlessness  when  compared  with 
the  strongly  poisonous  carbolic  acid. 

Thymol  dissolved  in  moderately  concentrated  warm  solution  of  potassium 
hydroxide,  gives  on  the  addition  of  a  few  drops  of  chloroform  a  violet  color, 
which  on  heating  soon  changes  into  a  beautiful  violet-red. 

Thymol  iodide,  Thymolis  iodidum,  (C6H,.CH3.C3H7.OI)2  =  545.76  (Di- 

thymol-diiodide,  Aristol,  Annidalin}.     Obtained  by  the  action  of  a  solution  of 


576  CONSIDERATION   OF  CARBON  COMPOUNDS. 

iodine  in  potassium  iodide  upon  an  alkaline  solution  of  thymol.  Condensation 
of  two  molecules  of  thymol  takes  place  with  the  introduction  of  two  atoms  of 
iodine  into  its  phenolic  group.  It  is  a  bright,  chocolate-colored,  or  reddish- 
yellow,  bulky  powder,  with  a  very  slight  aromatic  odor;  it  contains  46.14  per 
cent,  of  iodine  and  is  used  as  a  substitute  for  iodoform. 

Resorcinol,  CGH4(OH)2.  1:3  =  1O9.22  (Resorcin  9  Meta-dihydroxy- 
benzene).  It  is  formed  by  fusing  different  resins,  such  as  galbanum, 
asafoetida,  etc.,  with  caustic  alkalies,  but  it  is  now  made  almost  alto- 
gether from  benzene  by  heating  the  latter  with  fuming  sulphuric  acid 
to  257°  C.,  whereby  benzene-meta-disulphonic  acid,  C6H4(SO3H)2, 
is  produced.  The  sodium  salt  of  this  acid  is  fused  with  sodium 
hydroxide  for  several  hours,  forming  sodium  resorcin,  C6H4(ONa)2. 
The  mass  is  dissolved  in  water,  acidified,  and  extracted  with  ether, 
which  dissolves  out  the  resorcin.  This  is  further  purified  by  sub- 
limation and  recrystallization. 

Resorcinol  is  a  white,  or  faintly-reddish,  crystalline  powder,  having  a  some- 
what sweetish  taste  and  a  slightly  aromatic  odor;  it  fuses  at  119°  C.  (246°  F.), 
boils  at  276°  C.  (529°  F.),  and  is  soluble  in  less  than  its  own  weight  of  water. 
A  dilute  solution  gives  with  ferrric  chloride  a  bluish-violet  color.  Resorcinol, 
when  heated  for  a  few  minutes  with  phthalic  acid  in  a  test-tube,  forms  a  yel- 
lowish-red mass,  which,  when  added  to  a  dilute  solution  of  caustic  soda,  forms 
a  highly  fluorescent  solution.  Other  fluorescent  compounds  are  obtained  by 
heating  resorcinol  with  very  little  sulphuric  and  either  citric,  oxalic,  or  tar- 
taric  acid,  dissolving  in  a  mixture  of  water  and  alcohol  and  supersaturating 
the  solution  with  ammonia.  Resorcinol  is  largely  used  in  the  manufacture  of 
certain  dyes.  It  must  not  be  confused  with  the  proprietary  preparation  of  the 
same  name,  composed  of  equal  parts  of  resorcin  and  iodoform  fused  together. 

Quinol,  C6H4(OH)2.1 :  4  (Hydroquinone,  Para-dihydrozy-benzene),  is  formed 
by  dry  distillation  of  quinic  acid  (from  Peruvian  bark),  by  reduction  of 
quinone,  and  by  fusing  para-iodophenol  with  sodium  hydroxide.  It  occurs 
combined  with  sugar  as  the  glucoside  arbutin,  in  uva  ursi  (Bear-berry)  leaves. 
It  forms  small  plates  or  hexagonal  prisms,  melting  at  169°  C.,  easily  soluble  in 
hot  water,  alcohol,  and  ether.  Oxidizing  agents,  such  as  ferric  chloride,  chlo- 
rine, etc.,  convert  it  into  quinone,  C6H4O2.  It  is  used  as  a  developer  in  pho- 
tography. 

Solution  of  lead  acetate  gives  a  white  precipitate  with  pyrocatechol,  none 
with  resorcinol,  and  a  precipitate  only  in  the  presence  of  ammonia  with 
hydroquinol. 

Pyrogallol,  Pyrogallic  acid,  C6H3.(OH)3.  When  gallic  acid  is 
heated  to  200°  C.  (392°  F.)  it  is  decomposed  into  carbon  dioxide  and 
pyrogallol,  a  substance  which  is  not  a  true  acid,  but  a  tri-hydroxy- 
benzene — i.  e.,  a  phenol.  Pyrogallol  crystallizes  in  colorless  needles, 
melts  at  131°  C.  (268°  F.),  is  easy  soluble  in  water,  ether,  and  alco- 
hol. In  alkaline  solution  it  absorbs  oxygen  rapidly,  assuming  a  red, 


BENZENE  SERIES.     AROMATIC  COMPOUNDS.  577 

then  reddish-brown  and  dark-brown  color.  Nitric  acid  also  colors  it 
yellow,  then  brown,  and  this  property  is  made  use  of  in  testing  for 
traces  of  nitric  acid.  Solutions  of  silver,  gold,  and  mercury  are 
reduced  by  pyrogallol  even  in  the  cold. 


Gallacetophenone  or  Gallactophenone,  ^^<3    obtained  by 

heating  a  mixture  of  pyrogallol,  zinc  chloride,  and  glacial  acetic  acid  to  148° 
C.  It  is  a  crystalline  powder  of  dirty  flesh-color,  soluble  in  water,  introduced 
to  replace  pyrogallol,  which  is  poisonous. 

Phloroglucinol,  C6H3(OH)3.  1:3:5  (Phloroglucin,  Symmetrical  trihy- 
droxy-benzene),  results  when  resorcin  and  several  resins,  as  gamboge,  dragon's 
blood,  etc.,  are  fused  with  potassium  hydroxide.  It  forms  colorless  prisms, 
melting  at  218°  C.,  very  soluble  in  water  and  alcohol,  and  of  a  sweet  taste.  It 
stains  lignin  red  and,  together  with  vanillin,  is  used  to  detect  hydrochloric  acid 
in  stomach  contents. 

Hydroxy-hydroquinone,  C6H3(OH)3.  1  :  2  :  4,  is  the  third  trihydroxy- 
benzene.  It  is  an  interesting  fact  that  according  to  the  theory  as  to  the  struc- 
ture of  the  benzene  molecule,  three  isomeric  dihydroxy-benzenes  and  trihy- 
droxy-benzenes  should  exist,  and  in  each  case  three  actually  do  exist. 

Most  of  the  phenols  give  colors  with  ferric  chloride  solution,  and  are  acted 
on  by  the  oxygen  of  the  air  with  formation  of  colored  bodies.  They  are  un- 
stable toward  oxidizing  agents,  forming  in  many  cases  carbon  dioxide.  The 
di-  and  trihydroxyl  derivatives  are  less  stable  than  the  simple  phenols.  The 
same  is  true  also  of  hydroxy  acids  of  benzene,  for  example,  salicylic  and  gallic 
acids. 

Aromatic  alcohols  and  aldehydes. 

Aromatic  alcohols.  These  are  aromatic  derivatives  of  the  fatty  alcohols  — 
i  e.,  alcohols  in  which  hydrogen  of  the  fatty  hydrocarbon  residue  is  replaced  by 
a  benzene  derivative.  The  aromatic  alcohols  have  the  properties  of  true  fatty 
alcohols. 

Benzyl  alcohol,   CJJ^CHVOH,  is  the  simplest  member  of  the  class;  it  is 

isomeric  with  cresol,  C6H4<Q^3,  but  has  entirely  different  properties.     Benzyl 

alcohol  is  found  in  balsam  of  Peru  and  Tolu,  mostly  in  combination  with  ben- 
zoic  or  cinnamic  acid. 

Aromatic  aldehydes.  These  are  aromatic  derivatives  of  the  fatty  alde- 
hydes and  behave  in  all  respects  like  the  latter  ;  thus  they  combine  readily 
with  oxygen  to  form  acids  and  behave  generally  like  unsaturated  compounds. 

Benzaldehyde,  Benzaldehydum,  C6H5.COH  =  1O5.25.  This  is 
the  simplest  one  of  the  aromatic  aldehydes,  and  is  produced  artificially 
or  obtained  from  natural  oil  of  bitter  almonds  or  other  oils.  It  is  a 
colorless,  strongly  refractive  liquid,  having  a  bitter-almond-like  odor. 
It  is  easily  converted  into  benzoic  acid  by  oxidation. 

37 


578  CONSIDERATION  OF  CARBON  COMPOUNDS. 

Oil  of  bitter  almond,  Oleum  amyg-dalse  amarse.  Benzaldehyde 
does  not  occur  in  a  free  state  in  nature,  but  is  formed  by  a  peculiar 
fermentation  of  a  glucoside,  amygdalin,  existing  in  bitter  almonds,  in 
cherry-laurel,  and  in  the  kernels  of  peaches,  cherries,  etc.,  but  not  in 
sweet  almonds.  The  ferment  causing  the  decomposition  of  amygdalin 
is  a  substance  termed  emulsin,  which  is  found  in  both  bitter  and 
sweet  almonds.  As  water  is  required  for  the  decomposition,  the 
emulsin  does  not  act  upon  the  amygdalin  contained  in  the  same  seed 
until  water  is  added,  when  the  decomposition  takes  place  as  follows ; 

C20H27NOn    +     2H20    =    2C6H1206    -f    HCN    +     C7H6O. 
Amygdalin.  Water.  Glucose.         Hydrocyanic    Benzaldehyde. 

acid. 

The  oil  is  obtained  by  maceration  of  bitter  almonds  with  water, 
and  subsequent  distillation  when  it  distils  over  with  hydrocyanic 
acid  and  steam,  and  separates  as  a  heavy  oil  in  the  distillate. 

It  is  an  almost  colorless,  thin  liquid  of  a  characteristic  aromatic 
odor,  a  bitter  and  burning  taste,  and  a  neutral  reaction.  Pure  benz- 
aldehyde  is  not  poisonous,  but  the  oil  of  bitter  almond  is  poisonous 
on  account  of  its  containing  hydrocyanic  acid. 

Sitter-almond  water,  Aqua  amygdalae  amarce,  is  made  by  dissolving 
1  part  of  the  oil  in  999  parts  of  water. 

Cinnamic  aldehyde,  Cinnaldehydum,  C6H5.CH  :  CH.COH  =  131.07  (Arti- 
ficial oil  of  cinnamon,  Cinnamyl  aldehyde,  Phenyl  acrolein}.  This  aldehyde  is 
prepared  synthetically,  or  is  obtained  from  oil  of  cinnamon  by  extracting  with 
acid  sodium  sulphite.  Cinnamic  aldehyde  is  a  colorless  oil,  having  a  cinna- 
mon-like odor  and  a  burning,  aromatic  taste.  When  exposed  to  the  air  it  is 
oxidized  to  cinnarnic  acid. 

Vanillin,  Vanillhmm,  C6H3.OH.OCH3.COH.  4:3:1  =  150.92  (Methylpro- 
tocatechuic  aldehyde}.  Vanillin  is  the  active  constituent  in  vanilla  bean,  and  is 
made  artificially  in  a  variety  of  ways.  One  of  these  is  the  action  of  chloroform 
and  caustic  potash  on  guaiacol.  It  occurs  in  white,  crystalline  needles,  having 
the  odor  and  taste  of  vanilla,  and  melting  at  80°  to  81°  C.  It  is  soluble  in  100 
parts  of  cold  and  15  parts  of  warm  water,  easily  soluble  in  alcohol,  ether, 
chloroform,  and  dilute  alkalies.  It  is  extracted  completely  from  its  solution  in 
ether  by  shaking  with  a  saturated  aqueous  solution  of  sodium  bisulphite,  from 
which  it  may  be  precipitated  by  sulphuric  acid ;  it  is  also  extracted  by  ammo- 
nia water. 

,0  —  CO 

Ooumarin,  C6H,(  the  anhydride    of  ortho-hydroxy-cinnamic 

XCH=CH, 

acid,  is  found  in  the  Tonka  bean  and  resembles  vanillin  in  odor.  It  forms 
white,  shining  prisms,  melting  at  67°  C.,  and  soluble  in  400  parts  of  cold,  45 
parts  of  hot  water,  and  in  7.5  parts  of  alcohol ;  easily  soluble  in  ether. 

An  aqueous  solution  of  vanillin  is  turned  blue  by  a  few  drops  of  ferric  chlo- 
ride solution,  coumarin  is  not.  An  aqueous  solution  of  coumarin,  unlike  va- 


BENZESE  SERIES.     AROMATIC  COMPOUNDS.  579 

nillin,  forms  a  precipitate  when  iodine  in  potassium  iodide  is  added  in  excess, 
at  first  brown  and  flocculent,  and  afterward,  on  shaking,  forming  a  dark-green 
curdy  clot. 

"  Extracts  of  vanilla,"  made  not  from  the  vanilla  bean,  but  consisting  of 
alcoholic  tinctures  of  synthetic  vanillin  or  coumarin,  can  readily  be  detected  by 
evaporating  off  the  alcohol,  making  up  the  original  volume  with  water,  and 
acidifying  with  acetic  acid.  A  reddish-brown  precipitate  of  resin  is  formed  in 
the  case  of  a  true  extract,  but  none  in  the  artificial.  The  filtrate  from  this 
resin  gives  a  copious  precipitate  with  basic  lead  acetate  solution,  the  artificial 
extract  gives  none. 

Vanillin  has  been  found  adulterated  with  benzoic  acid,  acetanilide,  boric 
acid,  terpin  hydrate,  and  coumarin. 

Acids  of  the  benzene  series. 

These  are  derivatives  in  which  one  or  more  carboxyl  groups 
(COOH )  have  replaced  hydrogen  in  the  benzene  molecule.  Benzoic 
acid  is  the  simplest,  and  bears  the  same  relation  to  benzene  as  acetic 
acid  bears  to  methane.  Many  of  these  acids  are  found  as  natural 
products,  but  the  carboxyl  group  may  be  introduced  by  various  reac- 
tions, of  which  the  following  are  the  principal  ones  : 

1.  Oxidation  of  benzene  compounds  containing  fatty  hydrocarbon 
radicals  or  substituted  radicals  : 

C6H5CH2OH    +    20    =    C6H5COOH    +    H2O. 

2.  Hydrolysis  of  a  cyanide  by  heating  with  dilute  acid  : 

C6H5CN    +    2H2O    =    C6H5COOH    +    NH3. 

3.  The  treatment  of  alkali  salts  of  phenols  with  carbon  dioxide 
(see  Salicylic  Acid). 

Benzoic  acid,  Acidum  benzoicum,  HC7H5O2  or  C6H5CO2H  = 
121.13.  Found  in  benzoin  and  some  other  resins;  also  in  combination 
with  other  substances  in  the  urine  of  herbivorous  animals;  it  is 
obtained  from  benzoin  by  heating  it  carefully,  when  the  volatile 
benzoic  acid  sublimes.  It  is  now  also  manufactured  from  toluene, 
which  is  first  converted  into  benzo-trichloride  (trichlormethyl-ben- 
zene)  by  passing  chlorine  into  hot  toluene : 

C6H6CHS    +     6d    ==    C6H5CC13    +    3HC1. 

Benzo-trichloride,  when  treated  with  water  under  pressure,  yields 
benzoic  and  hydrochloric  acids,  thus: 

C6H5CC13     +     2H20    :   :    C6H5C02H    +    3HC1. 

Benzoic  acid  forms  white,  lustrous  scales  or  friable  needles,  which 
are  but  slightly  soluble  in  cold  water,  but  easily  soluble  in  alcohol. 


580  CONSIDERATION  OF  CARBON  COMPOUNDS. 

ether,  oils,  etc.  Shaken  in  solution  with  hydrogen  dioxide,  benzoic 
acid  is  converted  into  salicylic  acid. 

Benzoic  acid,  prepared  by  sublimation  from  gum  benzoin,  has  a 
slight  aromatic  odor  resembling  that  of  benzoin  ;  the  acid  obtained 
synthetically  is  odorless. 

Benzoic  acid,  when  neutralized  with  an  alkali,  gives  a  flesh-colored 
or  reddish  precipitate  of  ferric  benzoate  on  the  addition  of  a  neutral 
solution  of  ferric  chloride. 

By  neutralizing  benzoic  acid  with  either  ammonium  hydroxide, 
sodium  hydroxide,  or  lithium  carbonate,  the  official  salts  ammonium 
benzoate,  NH4C7H5O2,  sodium  benzoate,  NaC7H5O2.H2O,  and  lithium 
benzoate,  LiC7H5O2,  are  obtained.  The  three  salts  are  white,  soluble 
in  water,  and  have  a  slight  odor  of  benzoin. 

Benzoic  acid  and  its  derivatives,  taken  internally,  are  eliminated  in  the 
urine  as  hippuric  acid,  C6H5CO.NH.CH2COOH  (benzoyl-amino-acetic  acid), 
and  its  derivatives. 

Many  halogen,  nitro-  and  amino-benzoic  acids  exist  which  are  interesting 
in  pure  and  technical  chemistry. 

Ethyl  para-amino-benzoate,  C6H4(NH2)(COOC2H5)  (Anesthesiri),  is  a 
local  anesthetic,  introduced  as  a  substitute  for  cocaine.  It  is  a  white,  odorless, 
tasteless  powder,  melting  at  90°  to  91°  C.,  almost  insoluble  in  cold  and  diffi- 
cultly soluble  in  hot  water.  It  is  soluble  in  6  parts  of  alcohol.  When  placed 
on  the  tongue  it  produces  a  sensation  of  numbness. 

Benzoyl  chloride,  C6H5.COC1,  is  obtained  by  distilling  benzoic  acid  with 
phosphorus  pentachloride.  It  is  a  colorless,  irritating  oil,  boiling  at  200°  C., 
slowly  decomposed  by  cold  water,  but  more  stable  than  acetyl  chloride.  It 
acts  on  hydroxyl  compounds,  forming  benzoic  acid  esters,  thus  : 

C6H5.COC1    +    C6H5OH  C6H5COOC6H5    +    HC1. 

Phenyl  benzoate. 

This  process  of  introducing  the  benzoyl  radical  is  known  as  "  benzoylation."  It 
is  greatly  facilitated  when  carried  out  in  the  presence  of  alkali. 

Benzosulphinide,  Saccharin,  Benzosulphinidum,  C6H4.CO.SO2.- 
NH  =  181.77  (Anhydro-ortho-sulphamide-benzoic  acid,  Benzoyl  sul- 
pJionic-imide).  This  substance  is  a  derivative  of  benzoic  acid, 
C6H5.CO2H,  obtained  by  the  discoverers  from  toluene  by  the  trans- 
formations indicated  in  the  following  formulas  : 

CH3 


,CH3  /COOH  /CO, 

C.H  /  __>     C.H/  _>     C6H  /       >NH. 

-\soajra,  NSCVNH,  Nao/ 


Other  methods  of  preparing  saccharin  have  been  devised. 


BENZENE  SERIES.     AROMATIC  COMPOUNDS.  581 

Saccharin  is  a  white,  crystalline,  odorless  powder.  It  is  but  sparingly 
soluble  in  water,  requiring  about  250  parts  for  solution  ;  this  solution  is 
slightly  acid  and  has  an  extremely  sweet  taste,  which  is  yet  perceptible  when 
saccharin  is  dissolved  in  125,000  parts  of  water,  which  shows  that  it  is  about 
500  times  sweeter  than  cane-sugar,  a  solution  of  which  in  250  parts  of  water  is 
yet  perceptibly  sweet.  Saccharin  is  soluble  in  alcohol  and  ether,  and  it  is  this 
latter  property  which  is  made  use  of  in  testing  sugar  (or  other  substances  in- 
soluble in  ether)  for  saccharin.  The  substances  are  treated  with  ether,  which 
is  filtered  off  and  evaporated,  when  the  saccharin  may  be  recognized  by  its 
taste  in  the  residue. 

Saccharin  forms  very  soluble  and  well-crystallizing  salts  with  the  alkalies, 
which  are  also  intensely  sweet  ;  they  are  articles  of  commerce.  The  sodium 
salt  is  known  as  soluble  saccharin  or  krystallose.  Saccharin  is  known  in  the 
British  Pharmacopoeia  as  Glusidum  (Gluside),  and  in  commerce  as  glucusimide, 
saccharol,  saccharinol,  saccharinose,  agucarine,  etc.  A  number  of  preparations, 
such  as  antidiabetin,  contain  saccharin.  Dulcin  or  sucrol,  another  very  sweet 
substance,  is  para-phenetol-carbamide. 


Phthalic  acid,   C6H4QQg  Of  the  aromatic  polybasic 

acids,  the  dibasic  acids  are  the  most  important.  They  are  called 
phthalic  acids  in  allusion  to  the  fact  that  one  of  them  can  be  obtained 
from  naphthalene.  Theoretically,  three  dibasic  acids  are  possible  and 
all  are  known.  When  mixed  with  lime  and  distilled  they  yield 
benzene. 

Phthalic  acid  can  be  obtained  by  the  oxidation  of  derivatives  of 
benzene  containing  two  side-chain  hydrocarbons  in  the  ortho-position, 
but  it  is  manufactured  by  oxidizing  naphthalene  by  hot  fuming  sul- 
phuric acid  with  the  help  of  a  catalytic  agent,  as  mercury.  The  sul- 
phuric acid  loses  oxygen  to  the  naphthalene  and  forms  sulphur  diox- 
ide, which  escapes  in  great  quantities.  Enormous  quantities  of  phthalic 
acid  are  employed  in  the  manufacture  of  synthetic  indigo.  It  is  a 
crystalline  white  substance,  readily  soluble  in  hot  water,  alcohol,  and 
ether.  When  heated  it  decomposes,  yielding  water  and  phthalic 
anhydride,  which  latter  sublimes  in  long  needles  : 


Phthalic  anhydride. 


Iso-phthalic  acid  (Meta-phthalic  acid),  C6H4(COOH)21  :  3,  may  be  obtained  by 
oxidizing  benzene  derivatives  containing  two  side-chains  in  the  meta-position, 
and  from  rosin  by  oxidation  with  nitric  acid.  It  is  difficultly  soluble  in  water 
and  does  not  give  an  anhydride  when  heated. 

Terephthalic  acid  (Para-phthalic  acid),  C6H4(COOH).2l  :  4,  can  be  formed  by 


582  CONSIDERATION  OF  CARBON  COMPOUNDS. 

oxidation  of  turpentine  and  in  other  ways.     It  is  nearly  insoluble  in  water, 
alcohol,  and  ether,  and  does  not  yield  an  anhydride. 

Phenolphthalein.  When  phthalic  anhydride  is  heated  with  phenols 
and  concentrated  sulphuric  acid,  a  class  of  substances  is  obtained 
known  as  phthaleins.  The  simplest  of  these  is  phenolphthalein,  the 
composition  of  which  is  shown  in  the  following  reaction  : 


C6Hl\co>0    +   2C6H5-OH  =  C 

Phthalic  anhydride.  Phenol.  Phenolphthalein. 

It  occurs  as  a  creamy-white  powder  or  crystals,  soluble  in  600  parts 
of  water  and  in  10  parts  of  alcohol.  It  dissolves  in  alkaline  solu- 
tions with  a  beautiful  red  color,  and  is  used  as  a  sensitive  indicator  in 
acidimetry  and  alkalimetry.  Acids  destroy  the  red  color  by  reform- 
ing the  colorless  phenolphthalein  from  its  salts.  Taken  internally,  it 
acts  as  a  purgative,  but  appears  to  possess  no  further  physiological 
action.  For  adults  the  average  dose  is  0.1  to  0.2  Gm.,  given  as 
powder,  in  cachets,  capsules,  or  pills.  In  obstinate  cases  0.5  Gm. 
doses  may  be  given. 

Resordnolphthalein  or  fluorescein  is  obtained  by  heating  phthalic  anhydride 
and  resorcinol  at  210°  C.  with  zinc  chloride  as  a  dehydrating  agent.  It  is  a 
reddish-brown  substance  which  exhibits  an  intense  yellowish-green  fluores- 
cence in  an  alkaline  solution,  hence  its  name.  By  treatment  with  bromine  it 
forms  tetrabromfluorescein,  the  potassium  salt  of  which  is  the  dye  known  as 
eosin,  C20H6O5Br4K2.  This  is  a  valuable  stain  for  animal  and  plant  tissues.  In 
dilute  solution  it  shows  a  beautiful  rose  tint. 


Phenolsulphonephthalein,  C6H4^gQX)  .  This  substance  is  anal- 

ogous   to    phenolphthalein,    and    may   be    obtained    in    a    similar    manner 
by  heating  together  phenol  and  the  anhydride  of  orthosulphobenzoic  acid, 

C  H  /CO  \ 
6    4\cjn  /^>  which  is  analogous  to  the  anhydride  of  phthalic  acid.     The 


source  of  the  anhydride  of  sulphobenzoic  acid  is  saccharin. 

Phenolsulphonephthalein  is  a  red  or  brownish-red  powder,  soluble  in  alcohol, 
but  not  in  ether.  It  is  slightly  soluble  in  cold  water,  giving  a  deep  yellow 
color  to  the  solution,  but  readily  soluble  in  alkalies,  the  mono-sodium  salt 
having  a  bordeaux  red  color,  while  with  excess  of  alkali  the  solution  has  a 
beautiful  purple  color  similar  to  that  of  phenolphthalein  in  alkaline  solution. 
It  is  used  as  a  diagnostic  test  of  renal  efficiency  by  injecting  6  Mgm.  in  the 
form  of  the  mono-sodium  salt.  The  test  depends  upon  the  fact  that  normal 
kidneys  excrete  40  to  60  per  cent,  of  the  dose  during  the  first  hour  after  its 
first  appearance  in  the  urine,  whereas  kidneys  not  functioning  properly 
excrete  a  much  smaller  per  cent.  The  readings  are  made  by  means  of  a 
colorimeter. 


BENZENE  SERIES.     AROMATIC  COMPOUNDS.  583 


Hydroxy-acids  of  the  benzene  series. 

These  derivatives,  which  are  known  also  as  phenol-acids,  contain 
the  (OH)  and  (COOH)  groups  in  the  benzene  nucleus,  and  accord- 
ingly possess  the  properties  of  phenols  and  acids.  The  hydrogen  of 
the  (OH)  group  as  well  as  that  of  the  (COOH)  group  can  be  replaced 
by  a  metal  or  hydrocarbon  radical.  The  radical  introduced  into  the 
(COOH)  group  is  easily  removed  by  saponification,  as  in  the  case  of 
any  ethereal  salt,  whereas  that  introduced  into  the  (OH)  group  is  not. 

The  simplest  hydroxy-acids  are  those  containing  one  (OH)  group 
and  one  (COOH)  group.  There  are  three  such  acids,  namely,  ortho-, 
meta-,  and  para-hydroxy-benzoic  acid.  Of  these,  the  ortho  acid, 
known  better  as  salicylic  acid,  is  the  most  important. 

Salicylic  acid,  Acidum  salicylicum,  HC7H5O3  or  C6H4OH.CO2H 
=  137.  Derived  from  benzene  by  introducing  one  hydroxyl  and 
one  carboxyl  radical.  It  is  found  in  several  species  of  violet,  and  in 
the  form  of  methyl  salicylate  in  the  wintergreen  oil  (oil  of  Gaul- 
theria  procumbens).  May  be  obtained  by  fusing  potassium  hydroxide 
with  salicin. 

Nearly  all  salicylic  acid  used  medicinally  or  otherwise  is  obtained  by  syn- 
thesis. The  first  step  is  the  conversion  of  phenol  into  sodium  pheiiolate  by 
treatment  with  sodium  hydroxide,  thus  : 

C6H5OH    +    NaOH    =    C6H5ONa    +    H2O. 

Sodium  phenolate  is  next  dried  and  treated  with  carbon  dioxide,  when  direct 
combination  takes  place  and  sodium  phenol  carbonate  is  formed,  thus : 

C6H5ONa    +     C02    -a    NaC6H5C03. 

Sodium  Sodium  phenol 

phenolate.  carbonate. 

Sodium  phenol  carbonate  is  isomeric  with  sodium  salicylate  and  is  actually 
converted  into  the  latter  compound  by  being  heated  to  130°  C.  (266°  F.),  in 
tightly  closed  vessels,  or  in  vessels  through  which  carbon  dioxide  passes. 

Salicylic  acid  is  a  white,  solid,  odorless  substance,  having  a  sweet- 
ish, slightly  acrid  taste,  and  an  acid  reaction  ;  it  is  soluble  in  308  parts 
of  water  and  in  2  parts  of  alcohol ;  it  fuses  at  about  157°  C.  (315°  F.), 
and  sublimes  slowly  at  100°  C.  (212°  F.)  and  rapidly  at  140°  C. 
(281°  F.).  It  is  a  valuable  antiseptic. 

By  the  action  of  the  alkali  hydroxides  on  salicylic  acid,  the  various 
salts  may  be  obtained,  as,  for  instance,  sodium  salicylate,  NaC7H5O3, 
ammonium  salicylate,  NH4C7H5O3>  and  lithium  salicylate,  LiC7H5O3> 


584  CONSIDERATION  OF  CARBON  COMPOUNDS. 

all  of  which  are  official.  They  are  white  salts,  readily  soluble  in 
water.  In  the  presence  of  free  alkali,  the  solutions  absorb  oxygen 
from  the  air  and  become  colored.  Solutions  of  salicylates  are  incom- 
patible with  acids,  salicylic  acid  being  precipitated. 

Bismuth  subsalicylate  is  official  and  has  approximately  the  com- 
position, C6H4(OH)CO2BiO.  It  is  a  white,  amorphous  or  crystalline, 
odorless  and  tasteless  powder,  permanent  in  the  air,  and  almost  insol- 
uble in  water.  Alcohol  or  ether  extracts  salicylic  acid,  with  decom- 
position of  the  salt. 

Strontium  salicylate,  (C6H4(OH)CO2)2Sr  +  2H2O,  which  is  official, 
is  a  white  crystalline  powder,  odorless,  and  having  a  sweetish  saline 
taste.  It  is  soluble  in  18  parts  of  water  and  66  parts  of  alcohol.  It 
is  incompatible  with  ferric  salts,  mineral  acids,  quinine  salts  in  solu- 
tion, spirit  of  nitrous  ether,  sulphates  and  carbonates,  and  sodium 
phosphate  in  powder. 

Mercuric  salicylate,  C&H^QQ  /Hg,  is  prepared  by  heating  on  a  water- 
bath  21.5  parts  of  yellow  mercuric  oxide,  15  parts  of  salicylic  acid,  and  a  little 
water  until  the  mixture  is  perfectly  white.  It  occurs  as  a  white,  amorphous 
powder,  tasteless,  and  neutral  to  litmus  paper,  slightly  soluble  in  water  or  alco- 
hol, but  soluble  in  solutions  of  sodium  hydroxide  and  sodium  carbonate,  form- 
ing a  double  salt.  It  is  soluble  also  in  warm  solutions  of  chlorides,  bromides, 
and  iodides.  It  is  used  as  a  disinfectant,  and  as  a  remedy  in  syphilis  and  in 
certain  skin  diseases. 

Analytical  reactions. 

1.  Add  to  solution  of  salicylic  acid  or  its  salts  ferric  chloride:  a 
reddish-violet  color  is  produced,  yet  noticeable  in  solutions  containing 
1  part  of  salicylic  acid  in  500,000  parts  of  water. 

2.  Add  some  cupric  sulphate :  a  bright  green  color  will  result. 

3.  Dissolve  some  salicylic  acid  or  sodium  salicylate  in  methyl  alco- 
hol and  add  one-fourth  the  volume  of  sulphuric  acid.     Heat  gently 
and  set  aside  for  a  few  minutes.     On  reheating,  the  odor  of  methyl 
salicylate  is  developed. 

Aspirin,  C6H4.0(CH3CO)COOH  (Acetyl-salicylic  acid ),  is  obtained  by  the 
prolonged  action  of  acetic  anhydride  on  salicylic  acid  at  about  150°  C.  It  forms 
colorless  needles,  melting  at  135°  C.,  odorless,  and  of  an  acidulous  taste,  solu- 
ble in  100  parts  of  water  and  freely  in  alcohol  or  ether.  Boiling  water  or 
alkalies  decompose  it,  liberating  acetic  acid. 

Salicin,  C13H1807.     This  glucoside  is  found  in  several  species  of  Salix  (wil- 


BENZENE  SERIES.     AROMATIC  COMPOUNDS.  585 

low),  and  is  mentioned  here  because  it  splits  into  glucose  and  salicylic  alcohol, 
C6H4.OH.CH2OH,  when  boiled  with  dilute  acids: 

C13H1807  +  H20  =  C6H1206  +  C,H8Or 

Salicylic  alcohol  is  converted  by  chromic  acid  into  salicylic  aldehyde,  C6H< 
OH.COH,  which  by  further  oxidation  is  converted  into  salicylic  acid. 

Salicin  forms  white,  silky,  shining  needles,  which  are  soluble  in  less  than  an 
equal  weight  of  water,  have  a  neutral  reaction  and  a  very  bitter  taste. 

Salicin  sprinkled  upon  concentrated  sulphuric  acid  produces  a  red  color. 
Boiled  with  very  dilute  hydrochloric  acid  for  a  few  minutes,  and  this  solution 
nearly  neutralized  with  sodium  carbonate,  a  violet  color  is  produced  on  the 
addition  of  a  drop  of  ferric  chloride  solution. 

Methyl  salicylate,  Methylis  salicylas,  CH3,C7H503  or  C6H4(OH)COOCHS 

1  ".  2  =  150.92.  Oil  of  wintergreen  is  chiefly  methyl  salicylate,  a  nearly  color- 
less liquid  with  a  characteristic,  strongly  aromatic  odor.  It  is  made  by  the 
method  so  extensively  used  in  the  manufacture  of  esters,  viz.,  by  heating  of 
salicylic  acid  with  methyl  alcohol  in  the  presence  of  sulphuric  acid.  (See 
above  reaction  3  of  salicylic  acid,  )  It  is  also  found  in  many  other  volatile  oils, 
especially  in  oil  of  betula 

Phenyl  salicylate,  Salol,  Phenylis  salicylas,  C6H5.C7H5O3  or 
C6H4(OH)COOC6H5  1:2  =  212.47.  This  ester  is  a  white,  crystalline, 
almost  tasteless  powder,  which  is  nearly  insoluble  in  water,  readily 
soluble  in  alcohol,  ether,  and  benzol,  and  fuses  at  42°  C.  (107.4°  F.). 
It  is  used  as  an  antiseptic  and  antipyretic. 

Salol  heated  with  potassium  hydroxide  solution  causes  its  decom- 
position into  phenol,  which  can  be  recognized  by  its  odor,  and  potas- 
sium salicylate,  from  which  crystalline  salicylic  acid  will  separate 
upon  supersaturating  the  liquid  with  hydrochloric  acid.  An  excess 
of  bromine-water  produces  a  white  precipitate  in  an  alcoholic  solution 
of  salol. 

Salol  is  made  by  the  action  of  suitable  dehydrating  agents  upon  a 
mixture  of  phenol  and  salicylic  acid  : 

C6H5OH  -f  HC7H503  =  C6H5.C7H503  +  H2O. 

A  more  simple  method  for  its  manufacture  consists  in  the  heating 
of  salicylic  acid  between  220°  and  230°  C.  (428°  and  446°  F.)  in  an 
atmosphere  of  carbon  dioxide,  in  a  flask  with  a  long,  narrow  neck. 
The  reaction  is  this  : 


Anisic  acid,  O6H4<°£j^|  (Para-methoxy-benzoic  acid),  is  isomeric  with 
methyl  salicylate,  but,  unlike  the  latter,  it  is  not  saponified  when  heated  with 


586  CONSIDERATION  OF  CARBON  COMPOUNDS. 

alkalies.  This  is  due  to  the  fact  that  the  methyl  group  is  combined  as  in  an 
ether.  The  ether  groups,  as  OCH3,  OC2H5,  OC6H5,  etc.,  are  often  called  methoxy, 
ethoxy,  phenoxy,  etc.  Anisic  acid  is  formed  by  the  oxidation  of  anethol, 

OOH 

3,  an  ether  contained  in  oil  of  anise. 


Gallic  acid,  Acidum  gallicum,  HC7H5O5  -f  H2O  or  C6H2(OH)3.- 
CO2H  +  H2O  =  186.65.  Obtained  by  exposing  moistened  nut-galls 
to  the  air  for  about  six  weeks,  when  a  peculiar  fermentation  takes 
place,  during  which  taimic  acid  is  converted  into  gallic  acid,  which 
is  purified  by  crystallization.  The  crystals  contain  one  molecule  of 
water,  which  may  be  expelled  at  100°  C.  (212°  F.).  It  is  a  white, 
solid  substance,  forming  long,  silky  needles  ;  it  has  an  astringent  and 
slightly  acidulous  taste  and  an  acid  reaction  ;  it  is  soluble  in  about 
100  parts  of  cold  or  in  3  parts  of  boiling  water,  also  readily  soluble 
in  alcohol,  but  sparingly  in  ether  and  chloroform  ;  it  gives  a  bluish- 
black  precipitate  with  ferric  salts,  and  does  not  coagulate  albumin, 
nor  precipitate  alkaloids,  gelatin,  or  starch  (difference  from  tannic 
acid).  A  piece  of  potassium  cyanide  added  to  solution  of  gallic  acid 
produces  a  deep  rose-color. 

Bismuth  subgallate,  a  salt  which  is  somewhat  variable  in  composition,  is 
official.  It  is  a  yellow,  amorphous,  insoluble  powder,  known  as  Dermatol. 

Tannic  acid,  Acidum  tannicum,  C13H9O7.COOH  =  319.66 
(Gallotannic  acid,  Digallic  acid).  There  are  a  number  of  tannic 
acids,  or  tannins,  found  in  various  parts  of  different  plants  (oak-bark, 
nut-galls,  cinchona,  coffee,  tea,  etc.),  the  properties  of  which  are  not 
quite  identical.  All  tannins,  however,  are  amorphous,  have  a  faint 
acid  reaction  and  strongly  astringent  properties;  they  all  precipitate 
albumin  and  most  of  the  alkaloids  ;  they  give  with  ferric  salts  a  dark- 
colored  solution  or  precipitate,  the  color  being  dark  green  or  dark 
blue  ;  they  form  with  animal  substances  compounds  which  do  not 
putrefy.  Use  is  made  of  this  property  in  the  process  of  tanning  — 
i.  e.,  converting  hides  into  leather. 

The  official  or  tannic  acid  is  obtained  by  extracting  nut-galls  with 
ether  and  alcohol,  and  evaporating  the  solution  ;  it  forms  light-yel- 
lowish, amorphous  scales,  having  a  faint  and  characteristic  odor,  a 
strongly  astringent  taste,  and  an  acid  reaction  ;  it  is  easily  soluble  in 
water  and  diluted  alcohol. 

Analytical  reactions  : 

1.  To  solution  of  tannic  acid  add  ferric  chloride:  a  blue-black  pre- 
cipitate falls,  soluble  in  large  excess  of  tannic  acid  with  violet  color 


BENZENE  SERIES.     AROMATIC  COMPOUNDS.  587 

If  ferric  chloride  is  added  in  excess,  the  black  precipitate  dissolves  in 
it  with  green  color. 

2.  Add  a  few  drops  of  potassium  hydroxide  :  a  brown  coloration 
results. 

3.  To  a  dilute  solution  (1  in  100)  of  tannic  acid  add  a  small  quan- 
tity  of  lime-water.      A   pale   bluish-white,   flocculent  precipitate  is 
formed,  which  is  not  dissolved  on  shaking  (difference  from  gallic  acid), 
but  becomes  more  copious  and  of  a  deeper  blue  than  pinkish  by  the 
addition  of  an  excess  of  lime-water. 

4.  Tannic  acid  precipitates  solutions  of  gelatin,  albumin,  gelatinized 
starch,  tartar  emetic,  and  most  of  the  alkaloids. 

The  Naphthalene  series. 

Naphthalene,  Naphthalenum,  C10H8  =  127.10.  The  constitution 
of  all  benzene  derivatives  considered  so  far  may  be  explained  by  the 
introduction  of  radicals  in  benzene.  Naphthalene  and  its  derivatives 
must  be  assumed  to  be  formed  by  the  union  of  two  benzene  residues 
in  such  a  way  that  they  have  two  carbon  atoms  in  common,  as  repre- 
sented in  these  formulas  : 

H         H  H          OH 

H\CACAC/H 


<J     <!!     <"• 

P/*\0/W\0/\H  H/  Hc/    \c^   \H 

j.         i  A        1 

Naphthalene,  Ci0H8.  Naphthol,  Ci0HT.OH. 

Naphthalene  has  been  mentioned  as  a  product  of  the  destructive  distillation 
of  coal,  and  is  obtained  from  that  portion  of  coal-tar  which  boils  between  180° 
and  220°  C.  (356°  and  428°  F.).  This  distillate  is  treated  with  caustic  soda  and 
then  with  sulphuric  acid  and  distilled  with  water  vapor. 

When  pure,  naphthalene  forms  colorless,  lustrous  crystalline  plates,  having 
a  penetrating,  but  not  unpleasant,  odor  and  a  burning,  aromatic  taste.  It  fuses 
at  80°  C.  (176°  F.),  and  boils  at  218°  C.  (424°  F.),  but  volatilizes  slowly  at  ordi- 
nary temperature,  and  readily  with  water  vapor.  It  is  only  sparingly  soluble 
in  water,  but  easily  soluble  in  alcohol,  ether,  chloroform,  etc.  Impure  naph- 
thalene assumes,  when  exposed  to  light,  a  reddish  or  brownish  color.  Naph- 
thalene is  converted  into  phthalic  acid  by  oxidizing  agents. 

Derivatives  of  naphthalene.  While  benzene  yields  only  one  kind 
of  mono-substitution  product,  naphthalene  yields  two  varieties  in 
every  case.  Thus,  there  are  two  mono-hydroxy  derivatives  (naph- 


588  CONSIDERATION  OF  CARBON  COMPOUNDS. 

thol),  two  mono-amino  derivatives  (naphthylamine),  etc.  This  is 
exactly  what  would  be  expected  if  the  formula  for  naphthalene  given 
above  be  true.  The  8  hydrogen  atoms  in  the  molecule  fall  into  two 
groups  of  4  each,  the  atoms  of  each  group  bear  the  same  relation  to  the 
molecule,  but  different  from  the  relation  that  the  atoms  of  the  other 
group  bear.  This  is  shown  in  the  following  formulas,  in  which  the 
hydrogen  atoms  are  designated  in  a  manner  that  permits  of  reference 
in  the  formulas  for  the  derivatives  of  naphthalene  : 

Ha3        Ha  8H          HI 


/33H         .a        X  Hj3  7H          (X  H2 

\c/   \c/ 


o 

x^Cs  /G^      /C\      ^C\ 

\H3 

II  II 

Ha'2       Ha1  H  5       H  4 


In  the  first  formula,  hydrogen  atoms  «,  a1,  a2,  a3  are  alike,  and  £, 
/51,  /52,  /5s  are  alike,  but  bear  a  different  relation  from  that  of  the  a 
hydrogen  atoms.  In  the  second  formula,  the  corresponding  groups 
are  1,  4,  5,  8  and  2,  3,  6,  7.  The  mono-substitution  products  in  which 
the  a  hydrogen  is  replaced,  are  known  as  alpha-  or  a-derivatives,  the 
others  as  beta-  or  ^-derivatives. 

Theoretically,  the  number  of  di-  and  tri-substitution  products  of 
naphthalene  is  very  large.  Thus,  ten  di-chlor  and  fourteen  tri-chlor 
derivatives  are  possible,  and  all  are  known.  Such  facts  as  these  leave 
very  little  doubt  as  to  the  truth  of  the  structural  formula  of  naphtha- 
lene as  given  above. 

Naphthol,  C10H7OH  =  142.98.  This  monatomic  phenol  bears  to 
naphthalene  the  same  relation  as  phenol  to  benzene — /.  <?.,  hydroxyl 
replaces  hydrogen  in  the  respective  hydrocarbons.  Two  isomeric 
naphthols,  the  alpha-  and  beta-naphthol,  are  known,  which  differ  in 
their  physical  properties  and  in  their  physiological  action.  The 
naphthol  which  is  used  medicinally  is  beta-naphthol,  a  solid  compound 
crystallizing  in  thin,  shining  plates,  having  an  odor  similar  to  phenol 
and  a  sharp,  pungent  taste.  It  fuses  at  122°  C.  (252°  F.),  boils  at 
286°  C.  (547°  F.),  is  soluble  in  about  1000  parts  of  cold,  or  75  parts 
of  boiling,  water ;  and  readily  soluble  in  alcohol,  ether,  chloroform, 
and  fatty  oils.  The  aqueous  solution  is  colored  greenish  by  ferric 
chloride.  A  few  drops  of  iodine  solution  added  to  an  aqueous  solution 
of  beta-naphthol,  followed  by  an  excess  of  alkali  solution,  should  pro- 


BENZENE  SERIES.     AROMATIC  COMPOUNDS.  589 

duce  no  color,  but  if  alplia-naphthol  is  present,  an  intensely  violet 
color  is  produced. 

Naphthol  occurs  in  coal-tar,  but  it  is  prepared  synthetically  from 
naphthalene  in  the  same  manner  in  which  phenol  is  prepared  from 
benzene.  When  concentrated  sulphuric  acid  is  heated  with  naphthalene 
for  several  hours  at  200°  C.,  the  beta-sulphonic  acid  is  formed,  C10H7- 
SO3H  ;  during  the  early  stage  of  the  process,  and  particularly  at  80°- 
90°  C.,  much  alpha-sulphonic  acid  is  formed,  but  at  a  higher  temper- 
ature this  is  converted  into  the  beta  variety.  The  sodium  salt  of  the 
beta  acid  is  fused  with  sodium  hydroxide,  forming  sodium  naphthol 
and  sodium  sulphite.  By  treating  the  former  with  an  acid,  beta-naph- 
thol  is  liberated,  which  must  be  further  purified. 

Microeidine,  C10H7.ONa,  is  the  name  given  to  sodium  naphthol. 
ItS  aqueous  solution  is  used  as  a  disinfectant  for  cleansing  dental 
instruments. 

Alpha-naphthol  is  obtained  in  the  same  manner  as  the  beta  product,  from 
the  sodium  salt  of  alpha-naphthalene  sulphonic  acid.  It  forms  lustrous  needles, 
melting  at  95°  C.  and  boiling  at  278°-280°  C.  It  is  more  readily  soluble  in  water 
than  beta-naphthol,  and  is  said  by  one  author  to  be  three  times  more  powerful 
as  an  antiseptic  and  only  one-third  as  poisonous  as  the  beta  compound.  It  is 
official  in  the  French  Pharmacopoaia.  Most  authorities  state,  however,  that  it  is 
more  poisonous  than  beta-naphthol.  It  has  been  used  as  a  test  for  sugar  in  urine 
and  is  employed  in  the  preparation  of  certain  azo  dyes,  as  is  also  beta-naphthol. 

The  naphthols  act  in  general  like  the  phenols,  but  the  (OH)  group  reacts 
more  readily  than  in  the  phenols.  Thus,  it  can  easily  be  replaced  by  the  amido 
(NH2)  group.  Naphthols  readily  form  sulphonic  acids,  of  which  many  are 
known  and  are  used  in  the  manufacture  of  azo  dyes.  The  1,  4,  naphthol-sul- 
phonic  acid  is  used  most. 

Beta-naphthol  benzoate,  C6H5COOC10H7  (Benzoyl-naphthol},\&  obtained  by  the 
action  of  benzoyl  chloride  on  beta-naphthol  at  170°  C.  It  is  a  white  crystalline 
powder,  melting  at  107°  C.,  tasteless,  odorless,  and  insoluble  in  water,  but  solu- 
ble in  alcohol,  chloroform,  and  hot  ether.  It  splits  into  beta-naphthol  and 
benzoic  acid  in  the  intestines. 

Beta-naphthol-bismuth  (Orphol]  has  approximately  the  composition,  C10H7O.- 
Bi2O2(OH),  and  is  said  to  be  formed  by  the  action  of  an  alkaline  solution  of 
naphthol  on  a  solution  of  bismuth  nitrate  in  dilute  glycerin.  It  is  a  light- 
brown,  odorless,  almost  tasteless  powder,  insoluble  in  alcohol  as  well  as  water. 
In  the  intestines  it  splits  into  naphthol  and  bismuth  hydroxide. 

Alpha-amino-naphthalene,  C10H7.NH2  (Alpha-nap hthy  famine],  is  obtained  by 
the  reduction  of  the  corresponding  nitro-naphthalene,  the  chief  product  of  the 
action  of  nitric  acid  on  naphthalene  in  the  cold.  It  is  also  formed  by  heating 
alpha-naphthol  with  the  ammonia  compound  of  zinc  chloride.  It  melts  at 
50°  C.,  has  a  pungent  odor,  and  turns  red  in  contact  with  air.  It  is  easily 
soluble  in  alcohol,  and  forms  crystalline  salts  with  acids,  the  solutions  of  which 
with  oxidizing  agents  give  a  blue  precipitate,  which  soon  turns  red. 


590  CONSIDERATION  OF  CARBON  COMPOUNDS. 

Beta-amino-naphthalene,  C10H7.NH2  (Beta-naphthy famine),  is  easily  obtained 
by  heating  beta-naplitbol  with  the  ammonia  compound  of  zinc  chloride  to  210°C. 
It  forms  pearly  scales,  soluble  in  hot  water,  ordorless,  and  melting  at  112°C.  It 
does  not  give  a  colored  compound  with  oxidizing  agents. 

Naphthionic  acid,  C10H6(NH2)SO3H  (1,  4,  Naphthylamine-sulphonic  add).  A 
number  of  sulphonic  acids  are  formed  when  the  naphthylarnines  are  treated  with 
sulphuric  acid,  some  of  which  are  valuable  in  the  preparation  of  dyes.  The 
sodium  salt  of  naphthionic  acid  is  used  in  making  congo  red,  which  has  the 

composition : 

C6H4.N2.C10H5(NH2)S03Na. 

C6H4.N2.C10H5(NH2)S03Na. 

Four  mono-sulphonic  acids  are  formed  when  beta-naphthylamine  is  treated 
with  sulphuric  acid. 

Santonin,  Santoninum,  C15H18O3  =  244.29,  is  an  anhydride  of 
santonic  acid,  C15H20O4.  As  several  reactions  point  to  a  relationship 
between  this  acid  and  naphthalene,  santonin  is  mentioned  in  this  place. 

Santonin  is  the  active  principle  of  wormseed,  the  unexpanded 
flowerheads  of  Artemisia,  from  which  it  is  obtained  by  extraction 
with  alcohol  and  lime-water,  and  decomposition  of  the  soluble  com- 
pound of  lime  and  santonin  by  an  acid.  Santonin  crystallizes  in 
colorless  prisms,  which  turn  yellow  on  exposure  to  light ;  it  is  but 
sparingly  soluble  in  water,  more  soluble  in  alcohol  and  ether. 

Santonin  taken  internally  confers  upon  the  urine  a  dark  color  re- 
sembling the  color  of  urine  containing  bile;  upon  heating  such  urine 
it  turns  cherry-red  or  crimson,  the  color  disappearing  on  the  addition 
of  an  acid,  and  reappearing  on  neutralization. 

Analytical  reactions : 

1.  Santonin  added  to  alcoholic  solution  of   potassium  hydroxide 
produces  a  bright-red  liquid  which  gradually  becomes  colorless. 

2.  To  1  c.c.  of  sulphuric  acid  add  a  few  drops  of  ferric  chloride 
solution  and  a  crystal  of  santonin  :  on  heating,  a  dark-red  color  is 
produced,  changing  into  violet-brown. 

Aromatic  compounds  containing-  nitrogen  in  the  cycle. 

Pyrrol,  C4H4NH.  During  the  destructive  distillation  of  certain 
nitrogenous  matters  (chiefly  bones),  a  liquid  known  as  bone-oil  is  ob- 
tained, which  contains  a  number  of  nitrogenous  basic  subtances, 
among  which  pyridine  and  pyrrol  are  found.  Pyrrol  has  but  weak 
basic  properties,  is  insoluble  in  water,  and  has  an  odor  like  chloroform. 


BENZENE  SERIES.     AROMATIC  COMPOUNDS.  591 

A  solution  of  pyrrol  in  alcohol,  treated  with  iodine  in  the  presence 
of  oxidizing  agents,  such  as  ferric  chloride,  deposits  after  some  time 
crystals  of  tctra-iodo  pyrrol.  This  compound  is  official  under  the 
name  of  iodol,  iodolum,  C4I4NH  =  566.17.  It  is  a  pale-yellow,  crys- 
talline powder,  almost  insoluble  in  water,  soluble  in  9  parts  of  alcohol, 
1  to  2  parts  of  ether,  and  15  parts  of  fatty  oils;  it  is,  when  pure, 
tasteless  and  odorless,  and  contains  of  iodine  88.97  per  cent. 

Antipyrine,  Antipyrina,  CUH12N2O  =  186.75  (Phenyl-dimethyl- 
isopyrazolon).  When  phenyl-hydrazine  is  heated  with  diacetic  ether, 
CH3CO.CH2.COOC2H5,  a  substance  is  formed  known  as  phenyl- 
methyl-isopyrazolon. 

In  this  compound  a  second  hydrogen  atom  may  be  replaced  by 
methyl,  when  phenyl-dimethyl-isopyrazolon  is  formed,  which  is  the 
substance  to  which  the  name  antipyrine  has  been  given. 

Antipyrine  is  a  white,  crystalline,  odorless  powder,  having  a  slightly  bitter 
taste;  it  fuses  at  113°  C.  (235°  F.),  is  soluble  in  less  than  its  own  weight  of 
water,  in  1  part  of  alcohol,  in  1  part  of  chloroform,  but  only  in  50  parts  of 
ether. 

The  structure  of  antipyrine  and  its  relation  to  pyrrol  and  isopyrazoltm  inay 
be  shown  by  the  constitutional  formulas: 

HC—  CH  HC—  CH  HC—  CH2 

HS  JH  I  JH  HH. 

NH  NH  NH 

Pyrrol.  Pyrazol.  Pyrazolin. 

HC—  CH2  HC=:CH  CH3—  C= 


i!r  co  HN  co 


co 

NC6H5 

Pyrazolon.  Isopyrazolon.  Phenyl-dimethyl- 

isopyrazolon. 

Analytical  reactions  : 

1.  0.2  gramme  of  antipyrine  dissolves  in  2  c.c.  of  nitric  acid  with- 
out change  of  color.    On  heating  slightly  the  liquid  assumes  a  yellow, 
then  an  intense  red  color. 

2.  12  c.c.  of  a  1  per  cent,  solution  of  antipyrine  treated  with  0.1 
gramme  of  potassium  nitrite  solution  yield  a  colorless  solution,  which 
turns  intensely  green  on  the  addition  of  1  c.c.  of  dilute  sulphuric  acid. 
In  a  more  concentrated  solution  green  crystals  of  isonitroso-antipyrine 
form  on  standing. 


592  CONSIDERATION  OF  CARBON  COMPOUNDS. 

3.  The  addition  of  ferric  chloride  to  solution  of  antipyrine  causes 
a  deep-red  color,  changing  to  yellow  on  the  addition  of  sulphuric 
acid. 

4.  Mercuric  chloride,  as  well  as  tannic  acid,  produces  a  white  pre- 
cipitate. 

Incompatibilities.  In  addition  to  those  indicated  in  the  above  tests,  the 
following  may  be  mentioned  :  A  mixture  of  antipyrine  and  calomel  produces 
a  poisonous  organic  mercury  compound ;  with  phenol,  even  in  dilute  aqueous 
solution,  an  oily  mass  is  formed;  rubbed  with  sodium  salicylate,  a  pasty  mass 
is  produced,  in  solution,  however,  there  seems  to  be  no  eftect ;  with  beta-naph- 
thol,  a  moist  mixture  results  ;  rubbed  with  chloral  hydrate,  an  oil  is  produced. 
On  the  other  hand,  antipyrine  increases  the  solubility  in  water  of  caffeine  and 
the  quinine  salts. 

Salipyrin  is  antipyrine  salicylate,  obtained  by  direct  combination  of  anti- 
pyrine and  salicylic  acid.  It  is  a  white  odorless  powder,  with  a  harsh,  sweetish 
taste,  and  is  almost  insoluble  in  water. 

Resopyrin  is  a  compound  of  antipyrine  and  resorcin.  Hypnal  is  a  com- 
pound of  antipyrine  and  chloral  hydrate.  Pyramidon  is  a  dimethyl-amido 
substitution  product  of  antipyrine.  Ferripyrine  is  a  combination  of  anti- 
pyrine and  ferric  chloride.  Many  other  combinations  are  known. 

Antipyrine  is  a  constituent  of  many  "  migraine  powders." 

Pyridine,  C5H5N.  This  substance  has  been  mentioned  above  as 
being  a  constituent  of  bone-oil.  Other  substances  have  been  isolated 
from  this  oil  and  have  been  found  to  form  a  homologous  series : 

Pyridine,  C5H5N  Lutidine,  C7H9  N 

Picoline,  C6H7N  Colliding  C8HUN 

Pyridine  is  of  special  interest,  because  it  has  been  found  that  sev- 
eral of  the  alkaloids,  such  as  quinine,  cinchonine,  etc.,  when  oxidized, 
yield  acids  containing  nitrogen,  which  bear  to  pyridine  the  same 
relation  that  benzoic  acid  bears  to  benzene,  or  that  acetic  acid  bears 
to  methane. 

Thus,  when  nicotine  is  treated  with  oxidizing  agents,  nicotinic 
acid,  C6H5NO2,  is  obtained,  which,  when  distilled  with  lime,  breaks 
up  into  pyridine  and  carbon  dioxide,  thus : 

C6H5N02  =  C5H5N  +  C02. 

The  relation  of  nicotinic  acid  to  pyridine,  of  benzoic  acid  to  ben- 
zene, acetic  acid  to  methane,  may  be  shown  thus : 


BENZENE  SERIES.     AROMATIC  COMPOUNDS.  593 

CH3.H  C6H6.H  C6H4N.H 

Methane.  Benzene.  Pyridine. 

CH3.C02H  C6H5.C02H  C5H4N.CO2H. 

Acetic  acid.  Benzoic  acid.  Nicotinic  acid. 

Pyridine  is  also  obtained  together  with  another  basic  substance, 
termed  quinoline,  C9H7N,  by  distilling  quinine  or  cinchonine  with 
potash.  These  observations,  showing  an  intimate  relationship  between 
alkaloids  and  the  pyridine  and  quinoline  bases,  have  led  to  numerous 
experiments  made  with  the  view  of  either  solving  the  problem  of 
making  alkaloids  synthetically,  or  of  obtaining  substances  which 
might  have  physiological  actions  similar  to  those  of  the  alkaloids. 
The  result  of  these  efforts  has  been  the  introduction  into  the  materia 
medica  of  quite  a  number  of  new  remedies. 

Pyridine  is  a  colorless  liquid,  having  a  sharp,  characteristic  odor, 
strongly  basic  properties,  and  a  boiling-point  of  116°  C.  (241°  F.). 

Quinoline,  C9H7N  (  Chinoline),  has  been  mentioned  above  as  a  product  of  the 
distillation  of  quinine  with  potash  ;  it  may  also  be  obtained  by  the  action  of 
sulphuric  acid  upon  a  mixture  of  aniline,  nitro-benzene,  and  glycerin.  It  is, 
like  pyridine,  a  colorless  liquid,  but  its  aromatic  odor  is  less  pleasant  and  its 
basic  properties  are  less  marked  than  those  of  pyridine.  Boiling-point  237°  C. 
(458°  F.). 

The  constitution  of  pyridine  and  quinoline  is  supposed  to  correspond  to 
benzene  and  naphthalene  respectively,  one  of  the  groups  CH  having  been  re- 
placed by  an  atom  of  nitrogen,  thus  : 

H  H         H  H         H 

! 


CX      /Cx       //CH  HQ,      /(\ 

^/  ^^  ^cx  x 


HC\      /CH  H 

\N/ 

H  H         H 

Pyridine.  Quinoline.  Isoquinoline. 

Isoquinoline  is  very  similar  to  quinoline,  but  differs  slightly  in  its  proper- 
ties. Like  quinoline  it  is  closely  related  to  a  number  of  alkaloids,  especially 
those  of  the  opium  group.  It  is  found  together  with  quinoline  among  the  bases 
of  coal-tar  and  bone-oil. 

Kairine,  C10H13.NO.HC1.  The  name  kairine  has  been  given  to  the  hydro- 
chloride  of  methyl-oxychinoline  hydride.  It  is  a  white,  crystalline,  odorless 
powder,  soluble  in  6  parts  of  water  or  in  20  parts  of  alcohol. 

Thalline,  C10HnNO  (Tetra-hydro-paramethyt-oxy  quinoline).    Quinoline  serves 

in  the  manufacture  of  thalline,  a  white,  crystalline  substance,  which  has  an 

aromatic  odor,  fuses  at  40°  C.  (104°  F.)  and  is  soluble  in  water,  alcohol,  and 

ether.    The  most  characteristic  feature  of  the  substance  is  that  it  is  colored 

38 


594  CONSIDERATION  OF  CARBON  COMPOUNDS. 

intensely  green  by  various  oxidizing  agents,  such  as  ferric  chloride  and  others. 
Some  of  the  salts  of  thalline,  chiefly  the  sulphate,  tartrate,  and  tannate,  have 
been  used  medicinally. 


51.   TERPENES  AND  THEIR  DERIVATIVES. 

The  group  of  hydrocarbons  of  the  general  formula  (C5H8)X,  found 
largely  in  the  volatile  oils,  has  been  called  by  the  generic  word  ter- 
penes, but  this  term  has  been  more  specifically  applied  to  the  sub- 
group C10H16.  According  to  the  molecular  complexity  this  group  has 
been  classified  into : 

Hemiterpenes C5H8, 

Terpenes  proper Ci0Hl6, 

Sesquiterpenes C15H24, 

Diterpenes C20H32, 

Polyterpenes (C10H16)X. 

Isopene  is  the  only  representative  of  the  hemiterpenes  found  in  a 
volatile  oil,  and  does  not  occur  naturally,  but  is  formed  by  the  de- 
structive distillation  of  rubber  or  gutta  percha.  The  terpenes  proper 
and  sesquiterpenes  are  among  the  principal  constituents  of  the  vola- 
tile oils.  The  diterpenes  and  higher  polyterpenes  are  more  rarely 
found  and  but  little  studied. 

Volatile  or  essential  oils.  The  term  essential  oil  is  more  a  phar- 
maceutical than  chemical  term,  and  is  used  for  a  large  number  of 


QUESTIONS. — What  is  the  difference  between  fatty  and  aromatic  compounds, 
and  from  which  two  hydrocarbons  are  they  derived  ?  From  what  source  is 
benzene  obtained,  how  can  it  be  made  from  benzoic  acid,  and  what  are  its 
properties  ?  Give  the  graphic  formulas  of  benzene,  nitro-benzene,  phenol, 
thymol,  benzoic  acid,  and  salicylic  acid.  Mention  methane  derivatives  which 
have  a  constitution  analogous  to  that  of  the  substances  mentioned.  Give  com- 
position, properties,  and  mode  of  manufacture  of,  and  tests  for  carbolic  acid. 
What  relation  exists  between  benzoic  acid  and  oil  of  bitter  almond?  What  is 
the  source  of  amygdalin,  to  which  class  of  substances  does  it  belong,  and  what 
are  the  products  of  its  decomposition  under  the  influence  of  emulsin  ?  Explain 
the  process  for  the  manufacture  of  salicylic  acid,  and  state  its  properties. 
Give  composition  and  properties  of  naphthalene  and  naphthol.  Give  tests  for 
tannin,  state  the  source  from  which  it  is  derived  and  for  what  it  is  used.  From 
what,  and  by  what  process,  is  aniline  obtained;  what  is  its  composition  and 
what  its  constitution?  How  are  aniline  dyes  manufactured  from  aniline? 
State  the  properties  and  some  reactions  characteristic  of  antipyrine.  What 
is  saccharin,  and  what  are  its  properties  ?  State  the  composition  of  iodol. 


TERPENES  AND   THEIR  DERIVATIVES.  595 

liquids  obtained  from  plants,  and  having  in  common  the  properties 
of  being  volatile,  soluble  in  ether  and  alcohol,  almost  insoluble  in 
water,  and  having  a  distinct  and  in  most  cases  even  highly  charac- 
teristic odor.  They  stain  paper  as  do  fats  or  fat  oils,  from  which 
they  differ,  however,  by  the  disappearance  after  some  time  of  the 
stain  produced,  while  fats  leave  a  permanent  stain. 

The  specific  gravity  of  volatile  oils  ranges  generally  between  0.85 
and  0.99.  Being  nearly  insoluble  in,  and  specifically  lighter  than, 
water,  they  will  float  on  it.  The  water,  however,  retains  in  most 
cases  enough  of  the  oils  to  assume  their  odor  (medicated  waters). 
Most  volatile  oils  are  optically  active,  turning  the  plane  of  polarized 
light  either  to  the  right  or  left.  While  chemically  pure  oils  are 
colorless,  many,  even  when  freshly  prepared,  have  a  distinct  color; 
some  are  pale  yellow,  dark  yellow,  reddish  or  reddish  brown,  while 
a  few  are  green  or  blue.  The  oils  generally  darken  with  age,  espe- 
cially when  exposed  to  light  and  air,  the  atmospheric  oxygen  acting 
on  them  and  converting  the  oils  often  into  a  sticky  and  resinous  mass. 

Volatile  oils  are  found  in  different  parts  of  plants,  and  are  the 
principles  imparting  to  the  respective  plants  their  characteristic  odor. 
The  extraction  of  volatile  oils  from  plants  is  accomplished  generally 
by  distilling  with  water  the  vegetable  matter  containing  the  oil,  the 
oil  passing  over  with  the  steam  and  floating  on  the  surface  of  the 
condensed  water.  In  some  instances  mechanical  pressure  is  used  for 
the  separation,  as  in  case  of  the  oils  of  orange,  lemon,  bergamot,  etc. 
In  other  cases  the  oils  are  extracted  by  suitable  solvents,  or  special 
methods  are  used. 

In  their  chemical  composition  essential  oils  differ  widely  ;  some  are 
compound  ethers  (oil  of  wintergreen  is  methyl  salicylate),  others  are 
aldehydes  (oil  of  bitter  almonds  is  benzaldehyde),  but  most  of  them 
are  hydrocarbons  of  the  aromatic  series,  or  mixtures  of  them,  often 
associated  with  oxygen  derivatives,  alcohols,  phenols,  ketones,  alde- 
hydes, esters,  etc. 

Oil  of  doves.  The  principal  constituent  of  this  oil  is  eugenol,  C8HS.C3H,. 
OCH3.OH,  a  monatomic  phenol ;  a  sesquiterpene,  C15H24,  culled  caryophylleue 
is  also  present. 

Oil  of  cinnamon  consists  chiefly  of  cinnamic  aldehyde,  C6H5CH.CHCOH, 
a  compound  which  has  been  prepared  synthetically.  Oil  of  cinnamon  also 
contains  cinnamyl  acetate,  C9H9.C,H3O2,  and  a  small  amount  of  cinnamic  acid 
C8H802. 

Oil  of  peppermint.  The  oils  found  in  the  market  differ  widely  from  one 
another,  and  there  is  no  other  volatile  oil  containing  so  many  different  con- 


596  CONSIDERATION  OF  CARBON  COMPOUNDS. 

stituents ;  as  many  as  seventeen  having  been  found  in  one  sample.  Besides 
three  different  terpenes  and  one  sesquiterpene,  were  found  acetaldehyde,  acetic 
acid,  isovalerianic  acid,  amyl  alcohol,  menthol,  menthon,  C10H180,  menthyl 
acetate,  C10H19O.C3H30,  and  others. 

Terpenes,  C10H16.  The  terpenes  are  widely  distributed  in  the 
vegetable  kingdom,  especially  in  the  coniferse  and  varieties  of  citrus, 
etc.,  and  are  found  in  the  volatile  oils  obtained  from  the  individual 
plants.  The  terpenes  are  readily  acted  upon  by  many  agents  and 
hence  undergo  numerous  changes.  One  of  these  changes  is  polym- 
erization— i.  e.,  conversion  into  compounds  of  the  composition  C^H^ 
and  CjjoHgg,  which  may  be  effected  by  heating  a  terpene  in  a  sealed 
tube,  or  by  shaking  it  with  concentrated  sulphuric  acid  or  with  cer- 
tain other  substances.  Many  of  them  also  show  a  great  tendency  to 
pass  into  more  stable  isomers  under  certain  conditions — i.  e.,  when 
acted  on  by  acids.  Gaseous  chlorine  acts  violently  upon  them,  and 
bromine  and  iodine  convert  many  of  them  into  cymene.  Many  ter- 
penes are  therefore  closely  related  to  cymene,  C10H14,  and  may  be  con- 
sidered as  dihydrocymene ;  others,  however,  show  a  quite  different 
structure.  They  are  oxidized  quite  readily  with  the  formation  of  a 
number  of  organic  acids,  and  unite  with  gaseous  hydrochloric  acid  to 
form  mono-  or  dihydrochlorides.  With  bromine  they  often  form 
characteristic  tetrabromides,  C10H16Br4.  They  readily  yield  com- 
pounds with  nitrosyl  chloride,  of  the  formula  C10H16.NOC1,  known 
as  nitrosochlorides,  and  with  the  oxides  of  nitrogen  compounds  of 
the  formulas  C10H16.N2O3  and  C10H16.N2O4,  known  as  nitrosites  and 
nitrosates  respectively.  The  terpenes  are  almost  all  optically  active, 
and  most  of  them  exist  both  in  dextro-  and  in  Isevorotatory  modifi- 
cations. 

Pinene  is  the  chief  constituent  in  most  of  the  volatile  oils  obtained 
from  the  coniferse,  and  is  also  found  largely  in  other  volatile  oils. 

Oil  of  turpentine,  C10H16,  is  chiefly  composed  of  pinene.  It  is  a 
thin,  colorless  liquid  of  a  characteristic  aromatic  odor,  and  an  acrid, 
caustic  taste ;  it  is  insoluble  in  water,  soluble  in  alcohol,  and  an  excel- 
lent solvent  for  resins  and  many  other  substances.  When  treated 
with  hydrochloric  acid  gas  direct  combination  takes  place  and  a  white 
solid  substance  of  the  composition  C10H16HC1  is  formed,  which  is 
known  as  pinene  hydrochloride,  or  artificial  camphor,  on  account  of 
its  similarity  to  camphor  both  in  appearance  and  odor. 

Experiment  7L  Through  10  or  20  c.c.  of  oil  of  turpentine  pass  a  current  of 
hydrochloric-acid  gas  for  some  time,  or  until  a  quantity  of  a  solid  substance 


TERPENES  AND   THEIR  DERIVATIVES.  597 

has  separated.    Collect  this  substance,  which  is  artificial  camphor,  upon  a  filter ; 
notice  its  characteristic  odor.     Heat  some  of  it;  hydrochloric  acid  is  set  free. 

Camphene  is  the  only  solid  hydrocarbon  of  the  terpene  group,  and  occurs  in 
the  oil  from  Pinus  Sibirica.  It  is  obtained  by  heating  the  above  pinene  hydro- 
chloride  with  alcoholic  potash. 

Limonene  is  the  principal  constituent  of  orange  oil,  and  is  found  in  a  large 
number  of  other  oils,  as  the  dextro  modification.  Laevolimonene  occurs  in 
pine-needle  oil. 

Dipentene  is  the  inactive  modification  of  limonene,  and  can  be  prepared  by 
heating  pineiie,  camphene,  sylvestrene,  or  limonene  to  250°-270°  C.  for  several 
hours. 

Terebene,  Terebenum,  consists  chiefly  of  dipentene  with  other  hydrocar- 
bons, and  is  obtained  from  oil  of  turpentine  by  mixing  it  with  sulphuric  acid, 
distilling,  washing  the  distilled  oil  with  soda  solution,  redistilling,  and  collect- 
ing the  portions  which  pass  over  at  a  temperature  of  155°-165°  C.  (311°- 
329°  F.).  Terebene  resembles  oil  of  turpentine  in  most  respects,  but  has  not 
the  unpleasant  odor  of  this  oil. 

Sylvestrene  is  found  in  Swedish  and  Russian  oil  of  turpentine. 

Phellandrene  is  widely  distributed  in  volatile  oils;  notably  in  the  water- 
fennel  oil  and  eucalyptus  oil. 

Sesquiterpenes,  C15H24.  These  are  likewise  widely  distributed  in 
the  vegetable  kingdom,  and  are  very  similar  in  their  general  proper- 
ties to  the  terpenes  proper,  but  have  a  higher  boiling-point.  Of 
those,  well  characterized,  may  be  mentioned :  cadinene,  from  oil  of 
cade  and  a  large  number  of  other  volatile  oils  ;  caryophyttene,  from  oil 
of  cloves ;  humulene,  from  oil  of  hops ;  santoleney  from  oil  of  sandal- 
wood;  cedrene,  from  oil  of  cedarwood ;  and  zingiberene,  from  oil  of 
ginger. 

Rubber,  Elastica  (Caoutchouc)  is  the  dried  milky  juice  found  in 
quite  a  number  of  trees  growing  in  the  tropics.  It  consists  chiefly 
of  hydrocarbons  of  the  terpene  series,  having  a  very  large  molecular 
weight  and  a  complex  molecular  structure. 

The  commercial  article  is  yellowish-brown,  has  a  specific  gravity 
of  0.92  to  0.94,  is  soft,  flexible,  insoluble  in  water  and  alcohol, 
but  soluble  in  carbon  disulphide,  ether,  chloroform,  and  benzene.  It 
is  not  acted  upon  by  dilute  mineral  acids ;  concentrated  nitric  and 
sulphuric  acid,  as  well  as  chlorine,  attack  it  after  a  time.  It  is  hard 
and  tough  in  the  cold ;  when  heated  it  becomes  viscous  at  125°  C. 
(257°  F.),  and  fuses  at  170°-180°  C.  (347°-356°  F.)  to  a  thick  liquid, 
which,  on  cooling,  remains  sticky,  and  only  regains  its  original  char- 
acter after  a  long  time. 

Vulcanized  rubbw  is  India-rubber  which  has  been  caused  to  enter 


598  CONSIDERATION  OF  CARBON  COMPOUNDS. 

into  combination  with  from  7  to  10  per  cent,  of  sulphur  by  heating 
together  the  two  substances  to  a  temperature  of  130°-150°  C.  (266°- 
302°  F.).  Vulcanized  rubber  differs  from  the  natural  article  by 
possessing  greater  elasticity  and  flexibility,  by  resisting  the  action  of 
solvents,  reagents  and  atmosphere  to  a  higher  degree,  and  by  not 
hardening  when  exposed  to  cold. 

Hard  rubber,  vulcanite,  or  ebonite,  is  vulcanized  rubber,  containing 
from  20  to  35  per  cent,  of  sulphur,  and  often  also  tar,  white-lead, 
chalk,  or  other  substances.  It  is  hard,  tough,  and  susceptible  of  a 
good  polish. 

Preservation  of  rubber.  Various  substances  have  been  recommended 
for  preserving  articles  of  rubber.  For  undeteriorated  rubber,  it  is  said  that  a 
3  per  cent,  solution  of  either  phenol  or  aniline  is  the  best,  while  for  deterior- 
ated rubber,  or  such  as  has  been  exposed  many  times  to  boiling  water,  a  1  per 
cent,  solution  of  potassium  pentasulphide  is  best,  the  restorative  properties  of 
the  latter  depending  on  the  absorption  of  the  sulphur  from  the  pentasulphide. 
The  articles  are  immersed  in  the  solutions  in  vessels  of  appropriate  shape.  It 
has  been  observed  that  black  rubber  immersed  in  the  aniline  solution  under- 
goes an  increase  in  volume.  For  example,  rubber  tubing  shows  a  marked  in- 
crease in  length. 

Gutta-percha  is  the  concrete  juice  of  a  tree — Isonaudra  gutta.  It 
resembles  india-rubber  both  in  composition  and  properties.  At  ordi- 
nary temperature  it  is  a  yellowish  or  brownish,  hard,  somewhat 
flexible,  but  scarcely  elastic  substance ;  when  warmed  it  softens,  and 
is  plastic  above  60°  C.  (140°  F.) ;  at  the  temperature  of  boiling-water 
it  is  very  soft.  It  is  insoluble  in  water,  alcohol,  dilute  acids  and 
alkaline  solutions ;  soluble  in  oil  of  turpentine,  carbon  disulphide, 
and  chloroform. 

Oxygen  derivatives  of  terpenes. 

Stearoptens  or  camphors  are  substances  closely  related  to  the 
terpenes  and  to  cymene  both  in  physical  and  chemical  properties; 
while  terpenes  are  liquid,  camphors  are  crystalline  solids.  Borneo 
camphor  has  the  composition  C10H18O,  while  the  camphor  found 
in  the  camphor-trees  of  China  and  Japan  has  the  composition 
C10H160. 

Camphor,  Camphora,  C]0H16O  (LaurinoT),  forms  white,  translucent 
masses  of  a  tough  consistence  and  a  crystalline  structure ;  it  has  a 
characteristic,  penetrating  odor  and  poisonous  properties ;  in  the  pres- 
ence of  a  little  alcohol  or  ether  it  may  be  pulverized ;  it  is  nearly 
insoluble  in  water,  but  soluble  in  alcohol,  ether,  chloroform,  etc. ; 
boiled  with  bromine  it  forms  the  monobromated  camphor,  carnphora 


TERPENES  AND   THEIR  DERIVATIVES.  599 

monobromata,  C,0H15BrO,  a  white  crystalline  substance  having  a  mild 
camphoraceous  odor  and  taste.  Heating  with  nitric  acids  converts 
camphor  into  camphoric  add,  acidum  camphoricum,  CgH^CO.,!!)^ 
a  colorless,  crystalline,  fusible  substance  having  an  acid  taste  ;  it  is 
slightly  soluble  in  water,  readily  in  alcohol  and  ether. 

Cineol.  Eucalyptol,  C10Hi80,  is  found  in  the  volatile  oils  of  different  species 
of  eucalyptus,  as  also  in  the  oils  of  some  other  plants.  It  is  liquid  at  the  ordi- 
nary temperature,  but  solidifies  when  cooled  to  a  little  below  the  freezing-point 
of  water.  It  has  an  aromatic,  distinctly  camphoraceous  odor. 

Menthol,  C10H19OH  (Mint-camphor).  Found  together  with  a  ter- 
pene  in  oil  of  peppermint,  and  separates  in  crystals  on  cooling  the  oil. 
Menthol  is  nearly  insoluble  in  water,  fuses  at  43°  C.  (109°  F.),  and 
boils  at  212°  C.  (414°  F.).  It  has  the  characteristic  odor  of  pepper- 
mint. 

Terpin  hydrate,  Terpini  hydras,  C10H20O2.H2O,  is  the  hydrate  of 
the  diatomic  alcohol  terpin,  and  is  formed  from  pinene  under  the 
influence  of  alcohol  and  nitric  acid.  It  forms  colorless  crystals,  melt- 
ing at  117°  C.  (243°  F.),  is  readily  soluble  in  alcohol,  but  sparingly 
soluble  in  water,  ether,  or  chloroform. 

Resins  are  obtained,  together  with  the  essential  oils,  from  plants. 
Mixtures  of  a  resin  and  a  volatile  oil  are  known  as  oleo-resins,  while 
mixtures  of  a  resin  or  oleo-resins  and  gum  are  known  as  gum-resins. 
The  name  balsam  is  also  used  for  a  certain  group  of  oleo-resins. 

The  resins  are  mostly  amorphous,  brittle  bodies,  insoluble  in  water, 
but  soluble  in  alcohol,  ether,  fatty  and  essential  oils  ;  they  are  fusible, 
but  decompose  before  being  volatilized ;  they  all  contain  oxygen  and 
exhibit  somewhat  acid  properties. 

Turpentine,  the  oleo-resin  of  the  conifers,  contains  besides  the  oil  of 
turpentine  a  resin  called  colophony,  rosin,  or  ordinary  resin,  consisting 
chiefly  of  the  anhydride  of  abietic  acid,  C44H64O5. 

Copaiva  balsam  consists  of  a  volatile  oil  and  a  resin,  the  latter 
being  principally  copaivic  acid,  C20H30O2. 

Of  fossil  resins  may  be  mentioned  amber  and  asphalt,  the  latter 
having  most  likely  been  formed  from  petroleum. 

QUESTIONS. — What  substances  are  known  as  terpenes  :  where  are  they  found 
in  nature?  Give  the  composition  of  the  principal  groups  of  terpenes.  Men- 
tion the  general  properties  of  essential  oils,  and  name  some  of  the  important 
ones.  What  is  the  source  of  rubber  ;  how  is  it  converted  into  vulcanized  and 
hard  rubber  ?  State  the  composition  and  properties  of  camphor. 


600  CONSIDERATION  OF  CARBON  COMPOUNDS. 

52.  ALKALOIDS. 

General  Remarks.  The  basic  substances  found  in  plants  are 
grouped  together  under  the  name  of  alkaloids,  this  term  signifying 
alkali-like,  in  allusion  to  the  alkaline  or  basic  properties  of  these 
substances.  They  show  their  derivation  from  ammonia  to  a  more  or 
less  marked  degree,  as,  for  instance,  in  their  power  to  combine  with 
acids  to  form  well-defined  salts,  to  combine  with  platinic  chloride  to 
form  insoluble  double  compounds,  etc. 

The  compounds  formed  by  the  direct  combination  of  alkaloids  with 
acids  are,  in  the  case  of  oxygen  acids,  named  like  other  salts  of  these 
acids,  for  instance,  sulphates,  nitrates,  acetates,  etc.  In  the  case  of 
halogen  acids,  however,  a  different  method  has  been  adopted,  because 
it  would  be  incorrect  to  apply  the  terms  chlorides  and  bromides  to 
substances  formed  not  by  the  combination  of  chlorine  or  bromine  with 
other  substances,  nor  by  the  replacement  of  hydrogen  in  the  respective 
hydrogen  acids  of  these  elements,  but  by  direct  combination  of  these 
acids  with  the  alkaloids.  The  terms  hydrochloride  and  hydrobromide 
have  been  adopted  by  the  U.  S.  P.  for  the  compounds  obtained  by 
direct  union  of  alkaloids  with  hydrochloric  and  hydrobromic  acids. 
Formerly  the  terms  hydrochlorate  and  hydrobromate  were  used. 

Alkaloids  are  found  in  the  leaves,  stems,  roots,  barks,  and  seeds  of 
various  plants ;  it  often  happens  that  a  certain  alkaloid  is  found  in 
the  different  species  of  one  family,  and  it  is  often  the  case  that 

various  alkaloids  of  a  similar  composition  are  found  in  the  same  plant. 

General  properties  of  alkaloids: 

1 .  They  combine  with  acids  to  form  well-defined  salts,  and  are  set 
free  from  the  solutions  of  these  salts  by  alkalies  and  alkali  carbonates. 

2.  In  most  cases  those  containing  no  oxygen  are  volatile  liquids, 
those  containing  oxygen  are  non-volatile  solids. 

3.  The  volatile  alkaloids  have  a  peculiar  disagreeable  odor,  remind- 
ing of  ammonia ;  the  non-volatile  alkaloids  are  odorless. 

4.  Most  solid  alkaloids  fuse  at  a  temperature  above  100°  C.  (212° 
F.)  without  decomposition,  but  are  decomposed  when  the  heat  is 
raised  much  beyond  the  fusing-point. 

5o  Most  alkaloids  are  insoluble,  or  nearly  so,  in  water,  but  soluble 
in  alcohol,  chloroform,  benzene,  acetic  ether,  and  many  also  in  ether. 

6.  The  hydrochlorides,  sulphates,  nitrates,  acetates  (and  most  other 
salts)  of  alkaloids  are  either  soluble  in  water,  or  in  water  which  has 
been  slightly  acidulated,  and  also  in  alcohol ;  but  they  are  insoluble, 
or  nearly  so,  in  ether,  acetic  ether,  chloroform  (except  veratrine  and 


ALKALOIDS.  601 

narcotine),  amyl  alcohol  (except  veratrine  and  quinine),  benzene,  and 
benzin. 

7.  The  solid  alkaloids,  as  well  as  their  salts,  may  be  obtained  in  a 
crystalline  state. 

8.  Most  alkaloids  are  white,  have  a  very  strong,  generally  bitter, 
taste,  and  act  very  energetically  upon  the  animal  system. 

9.  From  the  aqueous  solutions  of  alkaloid  salts,  the  solid  alkaloids 
are  precipitated  by  alkali  hydroxides,  in  an  excess  of  which  reagents 
some   alkaloids   (morphine,   for   instance)   are   soluble.     Alkali  car- 
bonates and  bicarbonates  liberate  all,  and  precipitate  most  alkaloids ; 
not  precipitated  by  bicarbonates  are  strychnine,  brucine,  veratrine, 
atropine,  and  a  few  rare  alkaloids. 

Most  alkaloids  give  precipitates  with  tannic  acid,  picric  acid, 
phospho-molybdic  acid,  potassium  mercuric  iodide;  and  the  higher 
chlorides  of  platinum,  gold,  and  mercury.  These  precipitates  are 
similar  in  properties  and  composition  to  those  formed  with  ammonia. 

Most  alkaloids  give  beautiful  color  reactions  when  treated  with 
oxidizing  agents,  such  as  nitric  acid,  chloric  acid,  chromic  acid,  ferric 
chloride,  chlorine  water,  etc. 

A  decinormal  solution  of  mercuric-potassium  iodide,  HgI2.(KI)2,  made  by 
dissolving  13.546  grammes  mercuric  chloride  and  49.8  grammes  potassium 
iodide  in  1000  c.c  of  water,  is  known  as  Mayer's  solution.  This  precipitates  all 
alkaloids,  forming  with  them  white  or  yellowish-white,  generally  crystalline 
compounds.  The  solution  has  been  used  for  volumetric  determination  of  alka- 
loids, but  the  method  is  now  discarded,  as  the  results  are  not  accurate.  (In 
most  cases  the  alkaloid  replaces  the  potassium  in  the  potassium-mercuric  iodide.) 

Phospho-molybdic  acid,  mentioned  above  as  a  reagent  for  alkaloids,  is  pre- 
pared as  follows :  15  grammes  ammonium  molybdate  are  dissolved  in  a  little 
ammonia  water  and  diluted  with  water  to  100  c.c.  This  solution  is  poured 
gradually  into  100  c.c.  of  nitric  acid,  specific  gravity  1.185,  and  to  this  mixture 
Is  added  a  warm  6  per  cent,  solution  of  sodium  phosphate  as  long  as  a  precipi- 
tate is  produced.  This  precipitate  is  collected  on  a  filter,  washed  and  dissolved 
in  very  little  sodium  hydroxide  solution ;  the  solution  is  evaporated  to  dryness, 
further  heated  until  all  ammonia  has  been  expelled  and  the  residue  dissolved 
in  10  parts  of  water.  To  this  solution  is  added  a  quantity  of  nitric  acid  suffi- 
cient to  redissolve  the  precipitate  which  is  formed  at  first.  This  reagent  gives 
precipitates  not  only  with  the  alkaloids,  but  also  with  the  salts  of  potassium 
and  ammonium. 

General  mode  of  obtaining1  alkaloids.  The  disintegrated  veg- 
etable substance  (bark,  seeds,  etc.)  is  extracted  with  acidified  water, 
which  dissolves  the  alkaloids.  When  the  alkaloid  is  volatile,  it  is 
obtained  from  this  solution  by  distillation,  after  having  been  liberated 
by  an  alkali. 


602  CONSIDERATION  OF  CARBON  COMPOUNDS. 


volatile  alkaloids  are  precipitated  from  the  acid  solution  by 
the  addition  of  an  alkali,  and  the  impure  alkaloid  thus  obtained  is 
purified  by  again  dissolving  in  an  acid  and  reprecipitating,  or  by  dis- 
solving in  alcohol  and  evaporating  the  solution. 

As  the  quantity  of  alkaloids  in  plants,  and  consequently  in  the  aqueous 
extract  made  from  them,  is  often  so  small  that  the  precipitation  process  gives 
unsatisfactory  results,  a  second  method  known  as  the  shaking-out  process  is  often 
employed  for  the  separation  of  alkaloids.  In  using  this  process  the  con- 
centrated aqueous  extract,  to  which  a  suitable  alkaline  precipitant  has  been 
added,  is  agitated  with  a  liquid  (such  as  chloroform)  not  miscible  with  water 
and  acting  as  a  solvent  upon  the  alkaloids.  The  operation  is  performed  in  an 
apparatus  known  as  separator  or  separatory  funnel,  consisting  of  a  globular  or 
cylindrical  glass  vessel,  provided  with  a  well-fitting  stopper  and  an  outlet-tube 
containing  a  glass  stopcock.  Having  introduced  into  this  vessel  the  extract 
and  solvent,  the  latter  is  made  to  dissolve  the  alkaloids  present  by  a  rapid 
rotation  of  the  separator.  As  the  aqueous  solution  and  the  solvent  do  not  mix, 
but  form  two  distinct  layers  one  above  the  other,  they  may  be  conveniently 
separated  by  opening  the  stopcock  until  the  heavier  liquid  has  run  out.  By 
evaporation  of  the  liquid,  used  as  a  solvent,  the  alkaloids  may  be  obtained  in  a 
more  or  less  pure  condition. 

Assay  methods.  As  the  medicinal  value  of  many  drugs,  such  as  opium, 
cinchona  bark,  etc.,  as  also  that  of  the  galenical  preparations,  such  as  tinctures, 
extracts,  etc.,  obtained  from  such  drugs,  depends  chiefly  on  the  alkaloids  pres- 
ent, and  as  the  quantity  of  the  alkaloids  in  drugs  varies  considerably,  the 
U.  S.  P.  gives  specific  assay  methods  for  the  estimation  of  the  percentage  of  the 
alkaloids  contained  in  drugs  or  in  certain  preparations. 

These  assay  methods  must  be  closely  followed  by  the  analyst,  as  otherwise 
results  may  be  obtained  which  are  either  too  high  or  too  low.  This  is  due  to 
the  fact  that  these  methods  in  many  cases  do  not  give  absolutely  correct  results, 
but  give  results  sufficiently  accurate  for  all  practical  purposes,  provided  the 
directions  of  the  Pharmacopeia  are  closely  followed.  To  bring  about  a 
standard  and  uniformity  in  alkaloidal  strength  is  the  object  of  these  assay 
methods. 

Antidotes.  In  cases  of  poisoning  by  alkaloids  the  stomach-pump  and  emetics 
(zinc  sulphate)  should  be  applied  as  soon  as  possible  ;  astringent  liquids  may  be 
given,  because  tannic  acid  forms  insoluble  compounds  with  most  of  the  alkaloids. 
In  some  cases  special  physiological  antidotes  are  known,  and  should  be  used. 

Detection  of  alkaloids  in  cases  of  poisoning1.  The  separation 
and  detection  of  poisonous  alkaloids  in  organic  matter  (food,  contents 
of  stomach,  etc.),  especially  when  present  in  very  small  quantities,  as 
is  generally  the  case,  is  one  of  the  most  difficult  tasks  of  the  toxi- 
cologist,  and  none  but  an  expert  who  has  made  himself  thoroughly 
familiar  with  the  methods  of  discovering  minute  quantities  of  organic 
poisons  in  the  animal  system  should  undertake  to  make  such  an 


ALKALOIDS. 


PLATE  VI 


norphine  treated  with  nitric  acid. 


Morphine    treated    with    solution    of 
ferric  chloride. 


Codeine    treated  with  bromine    water 
and  ammonia  water. 


Quinine    treated   with  chlorine   water 
and  ammonia  water. 


Strychnine     treated    with     sulphuric 
acid  and  potassium  dicbromate. 


Brucine  treated  with  nitric  acid  and 
with  sodium  thiosulphate. 


Physostigmine     treated     successively 

with    ammonia    water,  alcohol,  acetic   acid, 
and  again  with  ammonia  water. 


Veratrine  treated  with  sulphuric  acid. 


A  Jfofit&Co  Litli  Bulttntorr, .  \(d 


ALKALOIDS.  603 

analysis  in  case  legal  proceedings  depend  on  the  result  of  the 
chemist's  report. 

Of  the  various  methods  applied  for  the  separation  of  alkaloids  from  organic 
matter,  the  following  may  be  mentioned : 

The  substance  to  be  examined  is  properly  comminuted  (if  this  be  necessary) 
and  repeatedly  digested  at  40°  to  50°  C.  (104°  to  122°  F.)  with  water  slightly 
acidulated  with  sulphuric  acid.  The  filtered  liquids  (containing  the  sulphates 
of  the  alkaloids)  are  evaporated  over  a  water-bath  to  a  thin  syrup,  which  is 
mixed  with  three  or  four  times  its  own  volume  of  alcohol ;  this  mixture  is 
digested  at  about  35°  C.  (95°  F.)  for  several  hours,  cooled,  filtered,  and  again 
evaporated  nearly  to  dryness.  (By  this  treatment  with  alcohol  many  substances 
soluble  in  the  acidified  water,  but  insoluble  in  diluted  alcohol,  are  eliminated 
and  left  on  the  filter,  while  the  alkaloids  remain  in  solution  as  sulphates.) 

A  little  water  is  now  added  to  the  residue,  and  this  solution,  which  should  yet 
have  a  slight  acid  reaction,  is  shaken  with  about  three  times  its  own  volume  of 
acetic  ether,  which  dissolves  some  coloring  and  extractive  matters,  but  does  not 
act  upon  the  alkaloid  salts.  The  two  strata  of  liquids  which  form  on  standing 
in  a  tube  are  separated  by  means  of  a  pipette,  and  the  operation  is  repeated,  if 
necessary,  i.  e.,  if  the  ether  should  have  been  strongly  colored - 

The  remaining  acid  aqueous  solution  is  next  slightly  supersaturated  with 
sodium  carbonate,  which  liberates  the  alkaloids.  Upon  now  shaking  the  solu- 
tion with  acetic  ether,  all  alkaloids  are  dissolved  in  this  liquid,  which,  after 
being  separated  from  the  aqueous  solution,  leaves  upon  evaporation,  at  a  low 
temperature,  the  alkaloids  generally  in  a  sufficiently  pure  state  for  recognition 
by  special  tests.  It  may,  however,  be  necessary  to  purify  the  residue  further 
by  neutralizing  with  an  acid,  allowing  to  crystallize  in  a  watch-glass,  and  sep- 
arating the  small  crystals  from  adhering  mother-liquor. 

The  above  method  for  detecting  alkaloids  in  the  presence  of  organic  matter 
generally  answers  the  requirements  of  students. 

The  practical  toxicologist  has  in  most  cases  of  poisoning  some  data  (deduced 
from  the  symptoms  before  death,  or  from  the  results  of  the  post-mortem  exam- 
ination) pointing  to  a  certain  poison,  which,  of  course,  facilitate  his  work  con- 
siderably. 

Classificati9n  of  alkaloids.  While  the  constitution  of  many  alka- 
loids has  as  yet  not  been  determined,  others  have  been  shown  to  be 
derivatives,  or  to  contain  the  nuclei  of  either  pyridine,  quinoline,  or 
isoquinoline.  Closely  related  to  pyridine  are  the  liquid  bases  coniine, 
nicotine,  and  sparteine,  as  also  the  solid  alkaloids  atropine,  cocaine, 
ecgonine,  and  others.  Among  alkaloids  derived  from  quinoline  are 
those  found  in  cinchona  bark  and  in  nux  vomica.  Related  to  iso- 
quinoline are  the  opium  alkaloids. 

The  pyridine  group  of  alkaloids. 

The  close  relationship  between  pyridine  and  some  of  the  vegetable 
alkaloids  may  be  shown  by  considering  their  structure,  which  is  this : 


604  CONSIDERATION  OF  CARBON  COMPOUNDS. 

CH  CH2  CH2 

/%  /\  /\ 

HC      CH  H8C      CH2  H2C      CHa 

II       I  II  I        I 

HC      CH  H,C      CH2  H2C      CHC3HT 


N  NH  NH 

Pyridine.  Piperidine.  Coniine. 

Piperidine  has  been  made  by  adding  6  atoms  of  hydrogen  to  pyri- 
dine  by  means  of  sodium  and  alcohol  ;  coniine,  which  is  propyl-piperi- 
dine,  was  the  first  true  alkaloid  prepared  artificially. 

Piperin,  Piperina,  C17H19NO3  =--  283.04.  This  compound  is  found 
in  black  and  white  pepper.  While  it  is  isomeric  with  morphine,  it 
differs  widely  from  it  in  all  its  properties.  It  can  hardly  be  called 
an  alkaloid,  as  it  has  no  alkaline  reaction,  is  but  feebly  basic,  and  does 
not  show  the  general  alkaloidal  reactions.  The  U.  S.  P.  emphasizes 
this  by  giving  to  piperin  the  ending  in  and  not  ine,  which  is  used  for 
all  true  alkaloids.  It  forms  colorless  or  pale  yellowish  crystals 
which  are,  when  first  put  in  the  mouth,  almost  tasteless,  but  produce 
on  prolonged  contact  a  sharp,  biting  sensation. 

Piperin  dissolves  in  concentrated  sulphuric  acid  with  a  dark  blood- 
red  color,  which  disappears  on  dilution  with  water.  Treated  with 
nitric  acid  it  turns  rapidly  orange,  then  red. 

Coniine,  C8H17N,  occurs  in  conium  maculatum  (hemlock),  accom- 
panied by  two  other  alkaloids.  It  is  a  colorless,  oily  liquid,  having 
a  disagreeable,  penetrating  odor. 

Pilocarpine,  OUH16N2O2.  Found  in  the  leaflets  of  pilocarpus 
species.  The  alkaloid  crystallizes  with  difficulty  ;  its  solutions  in 
ether,  alcohol,  or  water  have  an  alkaline  reaction.  It  is  a  white, 
crystalline  powder,  which  dissolves  in  fuming  nitric  acid  with  a 
faintly  greenish  tint.  The  aqueous  solution  is  precipitated  by  most 
of  the  common  reagents  for  alkaloids.  The  hydrochloride  and  nitrate 
are  official. 

Nicotine,  C10H14N2.  Tobacco  leaves  contain  from  2  to  8  per  cent, 
of  nicotine,  which  is  a  colorless,  oily  liquid,  having  a  caustic  taste 
and  a  disagreeable,  penetrating  odor.  It  gives  with  hydrochloric 
acid  a  violet,  with  nitric  acid  an  orange,  color. 

Sparteine,  C15H26N2.  This  alkaloid,  found  in  scoparius  (broom, 
Irish  broom),  is  a  colorless,  oily  liquid,  turning  brown  on  exposure 
to  air  and  light.  It  has  a  slight  aniline-like  odor. 


ALKALOIDS.  605 

Sparteine  sulphate,  Ci5H26N.2H2S04  +  5H20,  is  obtained  by  saturating  the 
alkaloid  with  sulphuric  acid  ;  it  is  a  colorless,  crystalline  salt,  readily  soluble 
in  water.  An  ethereal  solution  of  the  salt,  to  which  a  few  drops  of  ammonia 
water  have  been  added,  deposits,  on  the  addition  of  an  ethereal  solution  of 
iodine,  minute  dark  greenish-brown  crystals. 

The  tropine  group  of  alkaloids. 


Atropine,  Atropina,  C^H^NOs  =  287.O4  (Daturine).  Obtained 
from  Atropa  belladonna.  It  is  a  white,  crystalline  powder,  having  a 
bitter  and  acrid  taste  and  an  alkaline  reaction  ;  it  is  sparingly  soluble 
in  water,  but  very  soluble  in  alcohol  and  chloroform.  The  commer- 
cial article  generally  contains  a  small  quantity  of  hyoscyamine. 
Atropine  sulphate,  (CtfH^NO^.ELjSO^  is  a  white,  crystalline  powder, 
easily  soluble  in  water. 

Analytical  reactions  : 

1.  Atropine  dissolves  in  concentrated  sulphuric  acid  without  color. 
This  solution  is  not  colored  by  nitric  acid  (difference  from  morphine), 
and  not  at  once  by  potassium  dichromate  (difference  from  strychnine). 
•"  2.  A  mixture  of  atropine  and  nitric  acid,  when  evaporated  to  dry- 
ness  over  a  water-bath,  leaves  a  yellow  residue,  which  turns  violet  on 
the  addition  of  a  few  drops  of  an  alcoholic  solution  of  potassium 
hydroxide  and  a  fragment  of  the  same  reagent. 

3.  On  warming  a  mixture  of  atropine  and  concentrated  sulphuric 
acid  a  pleasant  odor,  reminding  of  roses  and  orange  flowers  is  evolved. 
The  addition  of  a  few  fragments  of  potassium  dichromate  changes 
this  odor  to  that  of  bitter  almond. 

4.  Solutions  of  atropine  dilate  the  pupil  of  the  eye  to  a  marked 
extent. 

Homatropine,  C16H21NO3.  This  alkaloid  is  obtained  by  the  con- 
densation of  tropine  and  mandelic  acid.  The  hydrobromide  is  offi- 
cial. It  is  a  white  crystalline  powder,  and  resembles  atropine  in  its 
mydriatic  properties. 

Hyoscyamine,  C17H23NO3.  Found  in  small  quantities  together 
with  hyoscine  in  the  seeds  of  Hyoscyamus  niger  (henbane),  and  in 
some  other  plants  belonging  to  the  solanaceae. 

Hyoscyamine  resembles  atropine  closely  in  most  of  its  chemical, 
physical,  and  physiological  properties,  but  the  corresponding  salts  of 
the  two  alkaloids  crystallize  in  different  forms  ;  the  hydrobromide  and 
sulphate  are  official. 


606  CONSIDERATION  OF  CARBON  COMPOUNDS. 

Hyoscyamine  differs  from  atropine  by  yielding  with  gold  chloride 
a  precipitate  which,  when  recrystallized  from  a  hot  aqueous  solution, 
acidified  with  hydrochloric  acid,  deposits  lustrous,  golden-yellow 
scales. 

Hyoscine,  C17H21NO4.  Found  together  with  hyoscyamine  in 
Hyoscyamus.  The  alkaloid  is  known  only  in  an  amorphous,  semi- 
solid  state,  but  the  salts,  of  which  the  hydrobromide  is  official,  crys- 
tallize readily.  Hyoscine  evaporated  to  dryness  on  a  water-bath  with 
a  few  drops  of  fuming  nitric  acid  leaves  a  nearly  colorless  residue 
which  turns  violet  on  the  addition  of  some  alcoholic  solution  of 
potassium  hydroxide. 

Scopolamine  hydrobromide,  C17H21NO4HBr3H2O,  is  the  hydro- 
bromide  of  an  alkaloid  obtained  from  plants  of  the  Solanacese,  and  is 
chemically  identical  with  hyoscine  hydrobromide. 

Cocaine,  Cocaina,  C17H21NO4  =  3OO.92.  This  alkaloid  is  found 
in  the  leaves  of  the  South  American  shrub  Erythroxylon  coca,  in 
quantities  varying  from  0.15  to  0.65  per  cent.  It  is  a  white  crystal- 
line powder,  soluble  in  about  600  parts  of  water,  easily  soluble  in 
alcohol,  ether,  and  chloroform  ;  it  fuses  at  98°  C.  (208°  F.).  A  frag- 
ment of  cocaine  placed  on  the  tongue  causes  the  sensation  of  numb- 
ness without  acrid  or  bitter  taste ;  the  solution  in  water  is  faintly  bitter. 

Cocaine  heated  with  acids  in  sealed  tubes  is  decomposed  into  methyl  alcohol, 
benzoic  acid,  and  ecgonine,  showing  it  to  be  methyl-benzoyl-ecgonine : 

C12H21NO4  +  2H2O  =  CH3HO  +  G6H5CO2H  +  C9H15NO3. 
Cocaine.  Methyl  alcohol.   Benzoic  acid.          Ecgonine. 

Ecgonine  is  found  in  the  coca  leaves  as  benzoyl-ecgonine,  C9HI5(C7H50)N03 
+  4H2O ;  this  is  a  white,  crystalline  substance  from  which  cocaine  may  be 
obtained  by  heating  it  with  methyl-iodide.  The  mother-liquors  obtained  in 
the  manufacture  of  cocaine  from  the  leaves  contain  the  alkaloid  in  an  amor- 
phous state  and  possibly  one  or  two  other  alkaloids,  one  of  which  has  been 
named  hygrlne.  Whether  these  alkaloids  are  contained  in  the  coca-plant,  or 
are  products  of  the  decomposition  of  cocaine,  are  questions  not  yet  decided. 

Of  the  various  salts  of  cocaine,  the  hydrochloride,  C17H21NO4HC1, 
is  official.  This  salt  crystallizes  from  alcohol  in  short,  anhydrous 
prisms;  from  aqueous  solution,  however,  with  two  molecules  of  water, 
which  are  completely  expelled  at  a  temperature  of  100°  C.  (212°  F.). 
The  anhydrous  salt  fuses  at  190°  C.  (374°  F.)  and  is  readily  soluble 
in  water ;  this  salt  solution  has  a  somewhat  more  bitter  taste  than  the 
alkaloid  itself. 


ALKALOIDS.  607 

Analytical  reactions  : 

1.  Cocaine  salts  are  precipitated  from  an  aqueous  solution  as  fol- 
lows :  Platinum  chloride  produces  a  yellowish-white,  mercuric  chlo- 
ride a  white  nocculent,  picric  acid  a  yellow  pulverulent,  the  alkali 
carbonates  and  hydroxides  a  white  precipitate,  which  latter  is  soluble 
in  ammonia. 

2.  To  a  cocaine  solution,  strongly  acidified  with  hydrochloric  acid, 
add  some  potassium  dichromate,  when  an  orange-colored  crystalline 
precipitate  of  cocaine  chromate  forms. 

3.  Add  1  c.c.  of  a  3  per  cent,  solution  of  potassium  permanganate 
to  1  centigramme  of  cocaine  hydrochloride  dissolved  in  2  drops  of 
water;  a  violet  precipitate  forms  which  appears  brownish-violet  when 
collected  on  a  filter. 

4.  Boil  a  small  quantity  of  cocaine  solution  for  a  few  minutes  with 
dilute  sulphuric  acid  ;  neutralize  carefully  with  potassium  hydroxide 
and  then  add  a  few  drops  of  ferric  chloride  solution.    A  pale,  brownish- 
yellow  precipitate  of  basic  ferric  benzoate  will  form. 

Substitutes  for  cocaine.  Several  synthetics  have  been  introduced  to 
take  the  place  of  cocaine.  Some  of  these  are  the  following  : 

Alypin,  (CH3)2N.CH2.C(C2H5)(C6H5COO).CH2.N(CH3)2.HC1,  is  the  hydro- 
chloride  of  the  benzoyl-ethyl-tetramethyldiamido  derivative  of  secondary 
propyl  alcohol.  It  is  a  white  hygroscopic  powder,  very  soluble  in  water  and 
alcohol,  of  a  neutral  reaction  and  bitter  taste.  It  is  a  local  anesthetic,  claimed 
to  be  equal  to  cocaine,  but  not  a  mydriatic,  and  less  toxic  than  cocaine.  It  is 
used  externally  in  a  10  per  cent,  solution  and  hypodermically  in  a  1  to  4  per 
cent,  solution. 


Beta-eucaine  hydrochloride,  C5H7N.(CH3)3(  CeHsCOO^HCl,  is  a  salt  of 
trimethyl-benzoyl-hydroxypiperidine.  It  is  a  white  powder,  soluble  in  20 
parts  of  water  and  in  14  parts  of  alcohol.  Its  solutions  can  be  boiled  without 
change,  and  are  precipitated  by  alkalies  or  carbonates.  It  is  a  local  anesthetic 
like  cocaine,  but  weaker,  and  does  not  dilate  the  pupil  or  contract  the  blood- 
vessels. It  is  used  in  a  2  to  3  per  cent,  solution  in  the  eye,  and  5  to  10  per 
cent,  solution  or  ointment  on  other  parts. 

Holocaine  hydrochloride,  CH3,C(  :N.CeH4.OC2H5)(.NH.C6H4.OC2H5)JICl, 

is  the  salt  of  a  basic  condensation  product  of  paraphenetidin  and  acetparaphe- 
netidin  (phenacetin).  It  forms  colorless,  neutral  or  faintly  alkaline  crystals, 
odorless,  slightly  bitter,  and  producing  transient  numbness  on  the  tongue.  It 
is  soluble  in  50  parts  of  water,  easily  in  alcohol.  The  solution  is  precipitated 
by  alkalies  and  carbonates  and  the  alkaloidal  reagents.  Porcelain  should  be 
used  in  making  solutions,  as  alkali  from  glass  causes  a  turbidity. 

The  salt  is  a  local  anesthetic  like  cocaine,  but  having  a  quicker  effect  and 
antiseptic  action.  A  1  per  cent,  solution  is  employed.  It  is  more  toxic  than 
cocaine. 


608  CONSIDERATION  OF  CARBON  COMPOUNDS. 

Pelletierine  tannate  of  the  U.  S.  P.  is  a  mixture  of  the  tannates  of  four 
alkaloids  (ptmicine,  iso-punicine,  inethyl-punicine,  and  pseudo-punicine)  ob- 
tained from  Punica  Granatum. 

The  quinoline  group  of  alkaloids. 

Cinchona  alkaloids.  The  bark  of  various  species  of  cinchona 
contains  a  number  of  alkaloids,  of  which  the  most  important  are 
quinine,  cinchonine,  quinidine,  and  cinchonidine.  These  alkaloids 
exist  in  the  bark  in  combination  with  a  peculiar  acid,  termed  kinie 
acid.  The  quantity  and  relative  proportion  of  the  alkaloids  vary 
widely  in  different  barks,  but  the  official  bark  should  contain  not  less 
than  5  per  cent,  of  total  alkaloids,  and  at  least  4  per  cent,  of  anhy- 
drous ether-soluble  alkaloids. 

Quinine,  Quinina,  C20H24N2O2.3H2O  =  375.46.  This  formula 
represents  the  official  alkaloid,  but  it  is  also  known  anhydrous,  and 
in  combination  with  either  one  or  two  molecules  of  water.  The 
anhydrous  quinine  is  a  resinous  substance,  while  the  crystallized 
quinine  is  a  white,  flaky,  amorphous  or  crystalline  powder,  having 
a  very  bitter  taste  and  an  alkaline  reaction.  It  is  nearly  insoluble  in 
water,  but  soluble  in  alcohol,  ether,  ammonia  water,  chloroform,  and 
dilute  acids.  When  heated  to  about  57°  C.  (134°  F.)  it  melts ;  at 
100°  C.  (212°  F.)  it  loses  2  molecules  of  water,  the  remainder  being 
expelled  at  125°  C.  (257°  F.). 

Quinine  sulphate,  Quininse  sulphas,  (C20H24N2O2)2H2SO4.7H2O 
=  866.15.  This  salt,  containing  two  molecules  of  the  alkaloid  in 
combination  with  one  of  sulphuric  acid  and  seven  of  water,  is  the 
common  form  of  quinine  sulphate.  It  forms  snow-white,  silky,  light 
and  fine,  needle-shaped  crystals,  fragile  and  somewhat  flexible,  making 
a  very  light  and  easily  compressible  mass ;  it  has  a  very  bitter  taste 
and  a  neutral  reaction ;  it  is  soluble  in  720  parts  of  cold  and  in  30 
parts  of  boiling  water ;  soluble  in  65  parts  of  alcohol,  but  nearly 
insoluble  in  ether  and  chloroform ;  it  readily  dissolves  in  diluted 
sulphuric  or  hydrochloric  acid. 

Quinine  bisulphate,  Quininse  bisulphas,  C20H24N2O2.H2SO4.7H2O 
=  544.33.  This  salt  is  formed  when  the  common  sulphate  is  dis- 
solved in  an  excess  of  diluted  sulphuric  acid.  It  crystallizes  in  color- 
less, silky  needles,  has  a  strongly  acid  reaction,  and  is  soluble  in  8.5 
parts  of  water. 


ALKALOIDS.  609 

Quinine  hydrochloride,  C20H24N2O2.HC1.2H2O  =393.76. 
Quinine  hydrobromide,  C20H24N,O2-HBr.2H2O  =  420.06. 
Quinine  salicylate,  2(C20H24N2O2.C7H6O3)H2O  =  935.54. 

The  above  three  salts  are  obtained  by  treating  quinine  with  the  respective 
acids ;  they  are  white,  crystalline  substances ;  the  first  two  are  easily,  the  sali- 
cylate is  sparingly  soluble  in  water. 

Iron  and  quinine  citrate  is  a  scale  compound  obtained  by  dissolving  ferric 
hydroxide  and  quinine  in  citric  acid,  evaporating,  etc. 

Analytical  reactions : 

1.  Quinine  or  its  salts,  dissolved  in  water  or  in  dilute  acids,  give, 
after  having  been  shaken   with   fresh  chlorine  water,  or  bromine 
water,  an  emerald-green  color  on  the  addition  of  ammonium  hydrox- 
ide.    (Plate  YL,  4.) 

The  reaction  is  readily  shown  by  treating  10  c.c.  of  a  solution 
(about  1  in  1500)  with  2  drops  of  bromine  water,  and  then  with  an 
excess  of  ammonia  water.  The  green  color  is  due  to  the  formation 
of  thalleioquin. 

2.  Solutions  of  quinine,  treated  with  chlorine  water,  then  with 
fragments  of  potassium   ferrocyanide,  turn  pink,  then  red  on  the 
addition  of  ammonium  hydroxide  not  in  excess. 

3.  Solutions  of   quinine  give   with   ammonia  water  a  white  pre- 
cipitate of   quinine,   which   is  readily   dissolved    in   an    excess   of 
ammonia.     The  precipitate  is  also  soluble  in  about  twenty  times  its 
own  weight  of  ether  (the  other  cinchona  alkaloids  requiring  larger 
proportions  of  ether  for  solution). 

4.  Most  solutions  of  quinine,  especially  when  acidulated  with  sul- 
phuric acid,  show  a  vivid  blue  fluorescence. 

5.  Neutral  solutions  of  quinine  are  precipitated  by  alkaline  oxa- 
lates. 

6.  Quinine  and  its  salts  form  colorless  solutions  with  concentrated 
sulphuric  acid.     A  dark  or  red  color  indicates  the  presence  of  other 
organic  substances. 

Quinidine,  C20H24N2O2.  Isomeric  with  quinine;  it  gives,  like  the 
latter,  a  green  color  with  chlorine  water  and  ammonia,  and  forms 
fluorescent  solutions.  Unlike  quinine,  it  is  precipitated  from  neutral 
solutions  by  potassium  iodide. 

Cinchonine,  C19H22N2O.  This  alkaloid  is  found  in  cinchona  bark 
in  quantities  varying  from  0.5  to  3  per  cent.  It  crystallizes  without 
water,  forming  white  needles ;  it  is  almost  insoluble  in  water,  soluble 

39 


610  CONSIDERATION  OF  CARBON  COMPOUNDS. 

in  116  parts  of  alcohol  or  in  163  parts  of  chloroform,  readily  soluble 
in  dilute  acids. 

By  dissolving  the  alkaloid  in  sulphuric  acid  is  obtained: 
Cinchonine  sulphate,  Cinchonince  sulphas,  (C19H22N2O)2H2SO4.2H2O. 
It  is  a  white,  crystalline  substance.  Cinchonine  differs  from  quinine 
by  its  greater  insolubility  in  ether,  by  its  insolubility  in  ammonia 
water,  by  not  forming  fluorescent  solutions,  and  by  not  giving  a 
green  color  with  chlorine  water  and  ammonia. 

Analytical  reactions: 

"  1.  Chlorine  water  added  to  the  solution  of  a  cinchonine  salt  pro- 
duces a  yellowish-white  precipitate  insoluble  in  excess  of  ammonia. 

2.  Potassium  ferrocyanide  solution  added  to  a  neutral  solution  of 
cinchonine  produces  a  white  precipitate  soluble  in  excess  of  the  re- 
agent.     Upon   adding   an   acid   to   this   solution   a   golden-yellow 
precipitate  is  formed. 

3.  With  alkali  hydroxides,  carbonates,  and  bicarbonates,  cincho- 
nine salts  form  white  precipitates  insoluble  in  ammonia. 


Cinchonidine,  C^H^N^p.  An  alkaloid  isomeric  with  cinchonine; 
soluble  in  75  times  its  weight  in  ether.  The  sulphate,  which  crystal- 
lizes with  3  molecules  of  water,  is  official. 

Strychnine,  Strychnina,  C^H^N^  =  331.73.  This  alkaloid  is 
found,  together  with  brucine,  in  the  seeds  and  bark  of  different 
varieties  of  Strychnos,  and  is  generally  obtained  from  nux  vomica. 
Strychnine  is  a  white,  crystalline  powder,  having  an  intensely  bitter 
taste,  which  is  still  perceptible  in  solutions  containing  1  in  700,000. 
It  is  nearly  insoluble  in  water  and  in  ether,  soluble  in  chloroform 
and  in  dilute  acids. 

Strychnine  has  strong  basic  properties  and  is  one  of  the  most 
powerful  poisons  known,  one-quarter  of  a  grain  having  caused  death 
within  a  few  hours. 

By  dissolving  it  in  sulphuric  acid  or  nitric  acid  the  official  strych- 
nine sulphate,  strychnines  sulphas,  (C21H22N2O2)2.H2SO4.5H2O,  or 
strychnine  nitrate,  strychnince  nitras,  (C21H22N2O2.HNO3),  is  obtained. 

Analytical  reactions  : 

1.  Strychnine  dissolves  in  sulphuric  acid  and  nitric  acid  without 
color. 

j^2.  A  fragment  of  potassium  dichromate,  drawn  through  a  solution 
of  strychnine  in  concentrated  sulphuric  acid,  produces  momentarily  a 
blue,  then  brilliant  violet  color,  which  slowly  passes  to  cherry-red, 


ALKALOIDS.  611 

then  to  rose-pink,  and  finally  to  yellow.     This  reaction  may  still  be 
noticed  with  -g^-g^  grain  of  strychnine  (Plate  VI.,  5). 

3.  Sonnemchein's  ted.     When  to  a  very  small  quantity  of  strych- 
nine, dissolved  in  a  drop  of  sulphuric  acid,  some  ceroso-ceric  oxide  is 
added,  and  the  mixture  is  stirred  with  a  glass  rod,  a  deep-blue  color 
is  produced,  changing  soon  to  violet,  and  finally  remaining  cherry- 
red.     One  part  of  strychnine  in  one  million  parts  of  water  can  thus 
be  recognized.     The  reagent  may  be  made  by  heating  cerium  oxalate 
to  redness  and  dissolving  it  in  30  times  its  weight  of  sulphuric 
acid. 

4.  Solutions  of  strychnine  give  with  diluted  solution  of  potassium 
dichromate  a  yellow,  crystalline  precipitate,  which,  when  collected, 
washed,  and  heated  with  concentrated  sulphuric  acid,  shows  the  play 
of  colors  described  in  test  2.     A  play  of  colors  similar  to  the  above 
is  shown  under  identical  conditions  by  mixtures  of  other  alkaloids ; 
for  instance,  by  morphine  containing  10  per  cent  of  hydrastine. 

5.  Neutral  solutions  of  strychnine  give  yellow  precipitates  with 
the  chlorides  of  gold  and  platinum  and  with  picric  acid;  a  white 
precipitate  with   mercuric  chloride,  potassium  hydroxide,  and  with 
chlorine-water ;  a  greenish-yellow  precipitate  with  potassium  ferro- 
cyanide. 

Brucine,  C23H26N2O4.4H2O.  This  alkaloid  is  found  associated 
with  strychnine  in  various  species  of  Strychnos.  It  is  readily  soluble 
in  alcohol,  amyl  alcohol,  and  chloroform,  but  sparingly  soluble  in 
cold  water  and  in  ether. 

Analytical  reactions  : 

1.  To  1  c.c.  of  water  add  5  drops  of  nitric  acid  and  5  milligrammes 
of  brucine ;  a  deep  blood-red  color  results.     Heat  the  liquid  until  it 
has  assumed  a  yellow  color,  then  add  9  c.c.  of  cold  water  and  a  few 
milligrammes  of  sodium  thiosulphate  (or  a  small  crystal  of  stannous 
chloride) ;  a  beautiful  amethyst  or  violet  color  results  (Plate  VI.,  6). 

2.  Fresh  chlorine  water,  added  drop  by  drop  to  a  concentrated 
brucine  solution,  produces  a  red  color,  turning  violet,  and  becoming 
colorless  on  addition  of  an  excess  of  chlorine. 

Veratrine,  Veratrina.  This  is  a  mixture  of  alkaloids  obtained 
from  the  seed  of  Asagraa  officinalis.  It  is  a  white,  amorphous,  rarely 
crystalline  powder,  highly  irritating  to  the  nostrils  ;  nearly  insoluble 
in  water,  readily  soluble  in  alcohol. 

Analytical  reactions : 

1.  Concentrated  sulphuric  acid  causes  with  veratrine  first  a  yellow, 


612  CONSIDERATION  OF  CARBON  COMPOUNDS. 

then  reddish-yellow,  intense  scarlet,  and,  finally,  violet-red  color. 
(Plate  VI.,  8.)  The  yellow  or  orange-red  solution  exhibits,  by  re- 
flected light,  a  greenish  fluorescence. 

2.  Veratrine,  when  heated  with  concentrated  hydrochloric  acid, 
dissolves  with  a  blood-red  color. 

3.  Bromine  water  colors  veratrine  violet. 

4.  Veratrine  forms  with  nitric  acid  a  yellow  solution. 

The  isoquinoline  group  of  alkaloids. 

Opium  is  the  concrete,  milky  exudation  obtained,  in  the  Orient, 
by  incising  the  unripe  capsules  of  papaver  somniferum,  poppy. 
Chemically,  opium  is  a  mixture  of  a  large  number  of  substances, 
containing  besides  glucose,  fat,  gum,  albumin,  wax,  volatile  and 
coloring  matter,  meconic  acid,  etc.,  not  less  than  sixteen  or  eighteen 
different  alkaloids,  many  of  which  are,  however,  present  in  minute 
quantities. 

Ordinary  opium  should  contain  not  less  than  9  per  cent.,  and  when 
dried  at  85°  C.  (185°  F.)  not  less  than  12  per  cent,  nor  more  than 
12.5  per  cent,  of  morphine,  to  be  the  official  article.  Dried  and  pow- 
dered opium,  after  having  been  exhausted  with  purified  petroleum 
benzene  (which  dissolves  chiefly  the  narcotine,  but  not  the  morphine 
salts),  is  the  deodorized  opium  of  the  U.  S.  P. 

Morphine,  Morphina,  C17H19NO3.H2O  =  303  (Morphia).  A 
white  crystalline  powder,  or  colorless,  shining,  prismatic  crystals, 
odorless,  of  a  bitter  taste,  and  an  alkaline  reaction  to  litmus ;  almost 
insoluble  in  ether  and  chloroform,  very  slightly  soluble  in  cold 
water,  soluble  in  300  parts  of  cold,  and  36  parts  of  boiling,  alcohol ; 
heated  for  some  time  at  100°  C.  (212°  F.)  it  becomes  anhydrous ;  at 
254°  C.  (489°  F.)  it  melts,  forming  a  black  liquid. 

The  following  salts  are  official : 

Morphine  acetate,  Morphines  acetas,  C17H19NO3.C,H4O2.3H2O. 

Morphine  hydrochloride,   Morphinse  hydrochloridum,    C17H19NO3.HC1.3H2O. 
Morphine  sulphate,  Morphinae  sulphas,  (CnH19NO3)2H2SO4.5H2O. 

The  above  three  salts  are  white,  and  soluble  in  water. 

Analytical  reactions : 

1.  Morphine  or  a  morphine  salt  sprinkled  upon  nitric  acid  assumes 
an  orange-red  color,  and  then  produces  a  reddish  solution,  gradually 
changing  to  yellow.  (Plate  VI.,  1.) 

^,2.  Neutral  solution  of  ferric  chloride  causes  a  blue  color  with 
morphine  or  with  neutral  solutions  of  morphine  salts ;  the  color  is 


ALKALOIDS.  613 

changed  to  green  by  an  excess  of  the  reagent,  and  is  destroyed  by 
free  acids  or  alcohol,  but  not  by  alkalies.     (Plate  VI.,  2.) 

3.  A  fragment  of  iodic  acid  added  to  a  strong  solution  of  a  mor- 
phine salt  is  decomposed,  with  liberation  of  iodine,  which  imparts  a 
violet  color  to  chloroform  upon  shaking  the  latter  with  the  mixture. 

4.  A  mixture  of  2  parts  of  morphine  and  1  part  of  cane-sugar 
added  to  concentrated  sulphuric  acid  gives  a  rose-red  color. 

5.  Morphine  dissolves  in  cold,  concentrated  sulphuric  acid,  forming 
a  colorless  solution,  which,  after  standing  for  several  hours,  turns 
pink  or  red  on  the  addition  of  a  trace  of  nitric  acid. 

6.  Aqueous  or  acid  solutions  of  morphine  salts  are  precipitated  by 
alkaline  hydroxides ;  the  precipitated  morphine  is  soluble  in  potas- 
sium or  sodium  hydroxide,  but  not  in  ammonium  hydroxide. 

7.  Neutral  solutions  of  morphine  afford  yellow  precipitates  with 
the  chloride  of  gold  or  platinum,  with  potassium  chromate  or  dichro- 
mate,  and  with  picric  acid,  but  not  with  mercuric  chloride. 

Heroin,  C17H17(C2H3O2)2NO,  is  diacetyl-raorphine,  obtained  by  heating 
morphine  with  acetyl  chloride.  It  is  a  white  powder,  having  a  bitter  taste, 
alkaline  reaction,  and  practically  insoluble  in  water,  easily  soluble  in  hot  alco- 
hol. It  readily  forms  salts  with  acids,  the  one  usually  employed  being  the 
hydrochloride,  which  is  a  white  powder,  of  bitter  taste,  soluble  in  2  parts  of 
water  and  in  alcohol.  It  is  precipitated  by  alkalies,  carbonates,  and  alkaloid 
reagents. 

Apomorphine,  C17H17NO2.  When  morphine  is  heated  for  some 
hours  with  an  excess  of  hydrochloric  acid,  under  pressure  to  150°  C. 
(302°  F.),  it  loses  water  and  is  converted  into  apomorphine,  a  crys- 
talline alkaloid  valuable  as  an  emetic. 

Apomorphine  hydrochloride,  C17H17NO2.HC1  (U.  S.  P.),  is  a  grayish- 
white  salt  which  turns  greenish  when  exposed  to  light  and  air. 

Analytical  reactions : 

1 .  Nitric  acid  produces  a  deep  purple  color  fading  to  orange. 

2.  Sulphuric  acid  containing  a  trace  of  nitric  acid  produces  a  blood- 
red  color  fading  to  orange. 

3.  Sulphuric  acid  containing  a  trace  of  selenious  acid  produces  a 
dark  blue  color,  fading  to  violet,  then  turning  black. 

4.  Sulphuric  acid  containing  a  trace  of  ferric  chloride  produces  a 
pale  blue  color. 

Codeine,  Codeina,  C18H21NO3.H2O  =-•  314.83.  A  white  crystalline 
powder,  sparingly  soluble  in  cold  water,  easily  soluble  in  alcohol  and 
chloroform.  It  is  neutral  to  litmus  and  has  a  faintly  bitter  taste. 


614  CONSIDERATION  OF  CARBON  COMPOUNDS. 

Codeine  has  been  found  to  be  morphine  methyl-ether,  and  is  made 
synthetically  by  heating  morphine  with  methyl-iodide. 

Codeine  combines  with  acids  to  form  salts  soluble  in  water,  of  which 
the  following  are  official : 

Codeine  phosphate,    Codeinae  phosphas,     C18H21NO3.H3PO4.2H2O. 
Codeine  sulphate,       Codeinse  sulphas,        (C18H21NO3)2.H3SO4.5H2O. 

Analytical  reactions : 

1.  On  adding  to  5  c.c.  of  an  aqueous  solution  of  codeine  (1  :  100) 
10  drops  of  bromine  water,  shaking  so  as  to  redissolve  the  precipitate 
formed,  and  adding  after  a  few  minutes  some  ammonia  water,  the 
liquid  assumes  a  claret-red  tint.     (Plate  VI.,  3.) 

2.  Codeine  heated  with  sulphuric  acid  containing  a  drop  of  nitric 
acid  gives  a  blood-red  color. 

3.  Codeine,  dissolved  in  sulphuric  acid,  forms  a  colorless  liquid, 
which,  upon  being  warmed  with  a  trace  of  ferric  chloride,  becomes 
deep  blue. 

4.  Crystals  of  codeine  sprinkled  upon  nitric  acid  assume  a  red 
color,  but  the  acid  will  acquire  only  a  yellow,  not  a  red  color.     (Dif- 
ference from  morphine.) 

5.  Sulphuric  acid  containing  a  trace  of  selenious  acid  gives  a  green 
color,  changing  rapidly  to  blue,  and  then  slowly  back  to  grass-green. 

Dionin,  C19H2303N.HC1  4-  H20,  is  the  hydrochloride  of  the  ethyl  ester  of 
morphine,  which  is  similar  to  codeine,  the  methyl  ester  of  morphine,  and  is 
prepared  in  the  same  manner  as  the  latter.  It  is  a  white,  odorless,  slightly 
bitter  powder,  soluble  in  7  parts  of  water  and  2  parts  of  alcohol ;  insoluble  in 
ether  and  chloroform.  It  is  distinguished  from  morphine  salts  by  its  insolu- 
bility in  excess  of  alkali.  Some  authorities  claim  that  it  possesses  no  advan- 
tage over  codeine. 

Narcotine,  C22H23N07,  and  Narceine,  C23H27N08.3H.,0,  are  white  crystalline 
opium  alkaloids,  which  are  almost  insoluble  in  water,  soluble  in  alcohol. 
Concentrated  sulphuric  acid  forms  with  narcotine  a  solution  which  is  at  first 
colorless,  but  turns  yellow  in  a  few  minutes,  and  purple  on  heating.  Narceine 
dissolves  in  concentrated  sulphuric  acid  with  a  gray-brown  color,  which  changes 
to  red  when  heated. 

Stypticin,  C12H1303N.HC1  ( Cotarnine  hydrochloride),  is  a  salt  of  cotarnine, 
an  oxidation  product  of  narcotine,  similar  to  hydrastinine.  Cotarnine  is  ob- 
tained by  boiling  narcotine  for  a  long  time  with  water,  or  by  heating  it  with 
dilute  nitric  acid.  Stypticin  is  a  yellow  powder,  soluble  in  water  and  in  alco- 
hol. Its  solution  gives,  with  iodine  solution,  a  brown  precipitate  of  cotarnine 
periodide.  It  is  a  hemostatic,  analgesic,  and  uterine  sedative. 


ALKALOIDS.  615 

Meconic  acid,  C7H4O7.3H2O.  A  tribasic  acid,  characteristic  of 
opium,  in  which  it  exists  to  the  extent  of  3  or  4  per  cent.,  most 
likely  combined  with  the  alkaloids.  It  is  a  white,  crystalline  sub- 
stance, soluble  in  water  and  alcohol. 

Meconic  acid  forms  with  ferric  chloride  a  blood-red  color,  which  is 
not  affected  by  dilute  acids  or  by  mercuric  chloride  (different  from 
ferric  sulphocyanate),  but  disappears  on  the  addition  of  stannous 
chloride  and  of  the  alkali  hypochlorites.  This  test  may  be  used  in 
cases  of  poisoning  to  decide  whether  opium  or  morphine  is  present. 

Hydrastine,  Hydrastina,  C21H21N06  =  380.32.  Found  together  with  ber- 
berine  in  the  rhizome  of  Hydrastis  Canadensis  (golden  seal)  in  quantities  vary- 
ing from  0.1  to  0.2  per  cent.  Hydrastine  crystallizes  in  four-sided,  colorless 
prisms ;  it  fuses  at  131°  C.  (268°  F.),  is  insoluble  in  water  and  benzin,  soluble 
in  about  2  parts  of  chloroform,  124  parts  of  ether,  and  135  parts  of  alcohol  at 
the  ordinary  temperature. 

Hydrastine  answers  to  all  the.  general  tests  for  alkaloids;  treated  with  con- 
centrated sulphuric  acid  it  shows  a  yellow  color,  turning  red,  then  purple  on 
heating.  Concentrated  nitric  acid  produces  a  yellow  color,  changing  to  orange. 
The  fluorescence  noticed  in  solutions  of  hydrastine  or  its  salts  is  due  to  pro- 
ducts formed  from  it  by  oxidation.  While  hydrastine  itself  crystallizes  very 
readily,  especially  from  solutions  in  acetic  ether,  its  salts  can  scarcely  be 
obtained  in  crystals. 

Hydrastinine,  C11H11NO2.  When  hydrastine  is  treated  with 
oxidizing  agents  it  is  converted  into  hydrastinine,  the  hydrochloride 
of  which  is  official.  This  salt  has  a  pale-yellow  color,  a  bitter,  saline 
taste,  and  is  soluble  in  0.3  part  of  water,  and  also  readily  soluble  in 
alcohol,  but  difficultly  soluble  in  ether  or  chloroform.  A  dilute 
aqueous  solution  of  the  salt  (up  to  about  1  in  100,000)  has  a  decided 
blue  fluorescence. 

Berberine,  C20H17N04.  Found  in  a  number  of  plants  (Berberis  Tulgaris, 
Hydrastis  Canadensis,  etc.)  belonging  to  entirely  different  families.  It  is  a 
yellow,  crystalline  substance,  soluble  in  7  parts  of  alcohol,  18  parts  of  water, 
insoluble  in  ether,  chloroform,  and  benzene. 

Berberine  not  only  forms  well-defined,  readily  crystallizing  salts  with  acids, 
but  it  also  enters  into  combination  with  a  number  of  other  substances,  as,  for 
instance,  with  alcohol,  ether,  chloroform,  etc.  Some  of  these  compounds  crys- 
tallize well,  as  for  instance,  berberine-chloroform,  C20H17NO4.CHC13. 

The  xanthine  alkaloids. 

Caffeine  and  theobromine  are  xanthine  derivatives  and  are  closely 
connected  with  uric  acid.  They  show  the  properties  of  alkaloids  to 
a  much  less  degree  than  the  majority  of  the  compounds  considered  in 
this  chapter ;  they  do  not  act  on  red  litmus  and  are  but  feebly  basic. 


616  CONSIDERATION  OF  CARBON  COMPOUNDS. 

Theobromine  has  been  obtained  from  xanthine,  C5H4N4O2  (a  base  found  in 
animal  liquids),  by  treating  its  lead  compound  with  methyl-iodide,  CH8I,  when 
lead  iodide  and  dimethyl-xanthine  are  formed.  By  introducing  a  third  methyl 
group  into  the  molecule  of  theobromine  trimethyl-xanthine,  i.  e.,  caffeine  or 
theine  is  formed.  These  facts  show  the  close  relationship  between  the  active 
principles  of  the  vegetable  substances  used  so  extensively  in  the  preparation 
of  the  beverages,  coffee,  tea,  and  chocolate.  And  again,  these  principles  show 
a  relationship  to  a  series  of  substances  (such  as  xanthine,  uric  acid,  and  others) 
which  are  found  in  animal  fluids. 

Caffeine,  Caffeina,  C8H10N4O2.H2O  or  C5H(CH3)3N4O2.H2O  = 
210.64  (Trimethyl-xanthine,  Theine,  Guaranine),  occurs  in  coffee,  tea, 
Paraguay  tea,  and  a  few  other  plants.  It  forms  fleecy  masses  of  long, 
flexible,  silky  needles,  which  are  soluble  in  about  45  parts  of  water 
and  in  53  parts  of  alcohol ;  it  has  a  slightly  bitter  taste  and  a  neutral 
reaction. 

Caffeine  is  dissolved  by  sulphuric  acid  without  color ;  when  evapo- 
rated to  dryness  with  hydrochloric  acid  and  a  little  potassium  chlorate 
the  mass  assumes  a  purple  color  on  holding  it  over  ammonia-water. 

Two  volumes  of  a  saturated  solution  of  caffeine  in  water  mixed 
with  one  volume  of  mercuric  chloride  solution  form  after  a  short  time 
large  crystals  of  caffeine-mercuric  chloride. 

Oitrated  caffeine  (U.  S.  P.)  is  obtained  by  adding  caffeine  to  a  solu- 
tion of  citric  acid  and  evaporating  the  mixture  to  dryness. 

Theobromine,  C7H8N4O2  (Dimethyl-xanthine^).  Found  in  the  seeds 
of  Theobroma  cacao,  a  tree  growing  in  the  tropics.  It  is  white,  crys- 
talline, sparingly  soluble  in  cold  water,  alcohol,  and  ether,  volatilizes 
without  decomposition  at  290°  C.  (554°  F.),  has  a  neutral  reaction, 
but  forms  with  acids  well-defined  salts. 

Theobromine  sodium  salicylate,  C7H7N4O2.Na  -f  C7H5O3.Na  (Diure- 
tin),  is  a  double  salt  of  theobromine-sodium  and  sodium  salicylate.  It  is 
obtained  by  dissolving  in  water  molecular  proportions  of  sodium  hydroxide, 
theobromine,  and  sodium  salicylate,  and  evaporating  the  solution  to  dryness. 
It  is  a  white  powder,  containing  50  per  cent,  of  theobromine,  readily  soluble  in 
water,  and  easily  decomposed  by  exposure  to  carbon  dioxide  or  by  acids.  It  is 
incompatible  with  acids,  bicarbonates,  borates,  phosphates,  ferric  salts,  chloral, 
etc.  Its  effects  are  like  those  of  theobromine,  but  it  has  the  advantage  of 
greater  solubility. 

Unclassified  alkaloids. 

Physostigmine,  C15H21N3O2  (Eserine).  Found  in  the  seeds  of 
Physostigma  venenosum  (Calabar  bean).  The  pure  alkaloid  does  not 
crystallize  well,  is  almost  tasteless,  and  assumes  gradually  a  reddish 
tint.  The  sulphate  and  salicylate  are  official.  Both  are  white  or 
yellowish-white  crystalline  powders,  which  have  a  bitter  taste.  The 
sulphate  is  readily,  the  salicylate  sparingly  soluble  in  water. 


ALKALOIDS.  617 

Analytical  reactions  : 

1.  Five   milligrammes   of   physostigmiue   dissolved   in  2c.c.    of 
ammonia  water  yield  a  yellowish  -red  liquid  which,  on  evaporation 
on  a  water-bath,  leaves  a  blue  or  bluish  -gray  residue,  soluble  in 
alcohol,  forming  a  blue  solution.     Upon  supersaturation  with  acetic 
acid  this  becomes  violet  and  exhibits  a  strong  reddish  fluorescence. 
The  violet  solution  leaves  on   evaporation  a  residue  which  is  first 
green  and  afterward  blue.     (Plate  VI.,  7.) 

2.  Physostigmine  or  its  salts  give  with  calcium  oxide  and  water  a 
red  liquid  which  turns  green  on  heating. 

Aconitine,  Aconitina,  C34H47NOn.  Found  in  various  species  of 
aconitum  to  the  amount  of  about  0.2  per  cent.  It  is  a  white  crystal- 
line powder,  requiring  for  solution  3200  parts  of  water  or  22  parts 
of  alcohol. 

Aconitine  is  one  of  the  most  poisonous  substances  known  and 
should  never  be  tasted  except  in  highly  diluted  solutions,  which  cause 
a  characteristic  tingling  sensation  when  brought  in  contact  with  the 
mucous  surfaces  of  the  tongue.  A  dilute  aqueous  solution  is  precipi- 
tated by  alkalies,  tannic  acid,  mercuric  potassium  iodide,  but  only 
concentrated  solutions  yield  precipitates  with  platinic  chloride,  mer- 
curic chloride,  and  picric  acid. 

Any  soluble  salt  of  aconitine  in  dilutions  of  1  :  1000  produces 
with  a  drop  of  potassium  permanganate  solution  a  blood-red  precipi- 
tate of  aconitine  permanganate. 


Colchicine,  Colchicina,  C^H^NOg  =  396.23.  This  alkaloid  is 
obtained  from  Colchicum.  It  is  a  pale  yellow  amorphous  powder  or 
leaflets,  having  a  very  bitter  taste.  It  is  soluble  in  22  parts  of  water 
and  very  soluble  in  alcohol  and  chloroform.  It  melts  at  142°  C. 
(288°  F.).  Sulphuric  acid  produces  a  citron-yellow  color,  changed 
to  greenish-blue,  then  to  red,  and  finally  to  yellow  by  the  further 
addition  of  nitric  acid.  Excess  of  potassium  hydrate  changes  this 
to  red. 

Ptomaines  (Putrefactive  or  cadaveric  alkaloids).  It  has  been 
known  for  a  long  time  that  vegetable,  and  more  especially  animal 
matter,  when  in  a  state  of  decomposition  (putrefaction)  acts  generally 
as  a  poison,  both  when  taken  as  food  or  when  injected  under  the  skin. 
Though  many  attempts  had  been  made  to  isolate  the  poisonous  pro- 
ducts, this  was  not  accomplished  successfully  until  the  years  1873  to 


618  CONSIDERATION  OF  CARBON  COMPOUNDS. 

1876,  by  Francesco  Selmi,  of  Italy.  He  demonstrated  that  a  great 
number  of  basic  substances  can  be  extracted  from  putrid  matter  by 
treating  it  successively  with  ether,  chloroform,  amyl  alcohol,  and 
other  solvents.  He  also  showed  that  these  substances  resemble  vege- 
table alkaloids  in  many  respects,  and  assigned  to  them  the  name 
ptomaines,  derived  from  TITS/MO,  that  which  is  fallen — i.  e.,  a  cadaver. 
Although  Selmi  did  not  succeed  in  isolating  any  of  the  ptomaines 
completely  (he  experimented  with  extracts  only)  his  investigations 
stimulated  other  scientists,  and  by  the  united  efforts  of  many  workers 
our  knowledge  of  ptomaines  has  now  advanced  so  far,  that  general 
statements  can  be  given  in  regard  to  their  origin,  composition,  phys- 
ical and  chemical  properties,  action  upon  the  animal  system,  etc. 

Formation  of  ptomaines.  It  has  been  shown  in  Chapter  41  that 
albuminous  substances  under  favorable  conditions  undergo  a  decom- 
position termed  putrefaction.  Presence  of  moisture,  a  suitable  tem- 
perature, and  the  action  of  a  ferment  are  the  essential  factors  in 
putrefaction.  The  ferments  are  living  organized  beings,  termed 
germs,  bacteria,  bacilli,  microbes,  organized  ferments,  etc. 

It  is  during  the  growth,  development,  and  multiplication  of  these 
micro-organisms  that  the  decomposition  of  the  albuminous  sub- 
stances into  simpler  forms  of  matter  takes  place.  A  full  explanation 
of  the  exact  mode  of  the  formation  of  decomposition-products  from 
organic  matter  by  the  action  of  bacteria  has  not  been  furnished  yet, 
but  we  do  know  that  ptomaines  are  found  among  these  products. 
We  also  know  that  certain  bacteria  split  up  organic  molecules  in  a 
certain  direction,  i.  e.,  with  the  formation  of  certain  products.  We 
also  know  that  while  micro-organisms  live  chiefly  in  dead  organic 
matter,  they  also  have  the  power  of  existing  and  multiplying  in  the 
living  organism,  causing  the  decomposition  of  living  tissues,  often 
with  the  formation  of  ptomaines. 

General  properties  of  ptomaines.  Ptomaines  resemble  veg- 
etable alkaloids  in  all  essential  properties.  Some  contain  carbon, 
hydrogen,  and  nitrogen  only,  corresponding  to  the  volatile  alkaloids, 
such  as  coniine  and  nicotine,  while  others  contain  oxygen  also,  corre- 
sponding to  the  fixed  alkaloids. 

Ptomaines  and  alkaloids  both  have  the  basic  properties  and  the 
power  to  combine  with  acids  to  form  well-defined  salts ;  they  have  in 
common  a  number  of  characteristic  reactions,  such  as  the  formation  of 
precipitates  with  the  chlorides  of  platinum,  mercury,  gold,  as  also 
with  tannic  acid,  phospho-molybdic  acid,  picric  acid,  etc. ;  and  both 


ALKALOIDS.  619 

show  corresponding  solubility  and  insolubility  in  the  various  solvents 
generally  used  for  the  extraction  of  alkaloids. 

Ptomaines  not  only  possess  the  general  characters  of  true  alka- 
loids, but  even  the  often  highly  characteristic  color-tests  of  the  latter 
are  in  some  cases  almost  identical  with  those  of  ptomaines.  Thus, 
ptomaines  have  been  found  which  resemble  in  their  chemical 
properties  as  well  as  in  their  physiological  action  upon  the  animal 
system,  the  alkaloids  morphine,  atropine,  strychnine,  coniine,  digi- 
taline,  etc. 

Many  attempts  have  been  made  to  find  some  characteristic  prop- 
erties by  which  to  differentiate  between  the  putrefactive  and  the 
vegetable  alkaloids,  but  practically  without  results.  It  is  true  that 
most  vegetable  alkaloids  are  optically  active,  while  ptomaines  are 
inactive,  but  it  does  not  often  happen  that  ptomaines  are  obtained  in 
such  quantities  as  to  permit  of  an  exact  determination  of  optical 
properties. 

Under  these  conditions  it  is  evident  that  the  toxicologist  has  a  most 
difficult  task,  when  called  upon  to  examine  a  body  (especially  when 
already  in  a  state  of  decomposition)  for  alkaloidal  poisons.  How 
many  times,  in  former  years,  chemists  may  have  unjustly  claimed  the 
presence  of  poisonous  vegetable  alkaloids  in  material  given  them  for 
examination,  we  cannot  say,  but  we  do  know  of  a  number  of  cases 
of  recent  date  in  which  such  claims  were  shown  to  be  based  upon 
errors,  made  in  consequence  of  the  close  analogy  between  ptomaines 
and  alkaloids. 

While  the  poisonous  properties  of  some  ptomaines  are  well  marked, 
others  are  more  or  less  inert.  The  poisonous  ptomaines  are  now 
often  termed  toxines,  in  order  to  distinguish  them  from  the  inert 
basic  products  of  putrefactive  changes. 

The  toxines  are  of  special  interest  to  the  physician,  because  it  is 
now  known  that  infectious  diseases  are  caused  by  the  poisonous  prod- 
ucts formed  by  the  growth,  multiplication,  and  degeneration  of  micro- 
organisms in  the  living  body.  This  statement  is  of  far-reaching  im- 
portance, as  it  opens  a  new  field  for  investigation  in  connection  with 
the  treatment  of  infectious  diseases. 

Non-poisonous  ptomaines.  A  number  of  these  basic  substances 
have  been  known  for  a  long  time.  Some  of  them  are  also  formed  by 
other  processes  than  those  of  putrefaction,  and  the  term  ptomaines 
may,  therefore,  not  well  be  chosen  for  all  of  them.  However,  the 


620  CONSIDERATION  OF  CARBON  COMPOUNDS. 

close  relationship  between  these  substances  unites  them  into  a  natural 
group,  of  which  the  following  members  may  be  mentioned: 

Methylamine,  NH2.CH3,  the  simplest  organic  base  that  can  be  formed,  has 
been  found  in  decomposing  herring,  pike,  haddock,  poisonous  sausage,  cultures 
of  comma  bacillus  on  beef-broth,  etc.  It  is  an  inflammable  gas  of  strong  ain- 
moniacal  odor. 

Dimethylamine,  NH(CH3)2,  has  been  found  in  putrefying  gelatin,  decom- 
posing yeast,  poisonous  sausage,  etc.  It  is,  like  the  former,  a  gas  at  ordinary 
temperature. 

Trimethy  famine,  N(CH3)3,  has  been  shown  for  a  long  time  to  occur  in  some 
animal  and  vegetable  tissues.  Its  presence  has  been  demonstrated  in  leaves 
of  chenopodium,  in  the  blood  of  calves,  in  human  urine,  etc.,  but  it  also  occurs 
as  a  product  of  putrefaction  in  yeast,  meat,  blood,  ergot,  etc.  It  is  a  liquid, 
possessing  a  strong,  fish-like  odor.  Boiling-point  9°  C.  (48°  F.). 

Ethylamine,  NH2.C2H5;  DiSthylamine,  NH.(C2H5)2;  Triethylamim,  N.(C2H5)3; 
Propylamine,  NH2.C3H7;  Neuridme,  C5N2H14,  are  other  non-poisonous  volatile 
ptomaines  belonging  to  the  amine  group,  while  of  the  non-volatile  amides 
may  be  mentioned :  My  dine,  C8HUNO ;  Pyocyanine,  CUHUNO2 ;  Betaine,  C5H13 
N03,  etc. 

Poisonous  ptomaines.  While  no  strict  line  of  demarcation  can 
be  drawn  between  poisonous  and  non-poisonous  substances,  the  fol- 
lowing list  of  ptomaines  embraces  those  which  cause  serious  dis- 
turbances when  brought  into  the  animal  system : 

Isoamylamine,  C5H13N,  a  colorless,  strongly  alkaline  liquid,  has  been  found 
in  putrefying  yeast  and  in  cod-liver  oil .  It  is  strongly  poisonous,  producing 
rigor,  convulsions,  and  death. 

Cadaverine,  C5HUN2,  occurs  very  frequently  in  decomposing  animal  tissues, 
and  seems  to  be  a  constant  product  of  the  growth  of  the  comma  bacillus, 
irrespective  of  the  soil  on  which  it  is  cultivated.  It  is  a  syrupy  liquid,  pos- 
sessing an  exceedingly  unpleasant  odor,  resembling  that  of  coniine.  The  sub- 
stances which  have  been  described  by  various  scientists  as  "  animal  coniine  " 
were  most  likely  cadaverine.  This  base  is  not  very  poisonous,  but  is  capable 
of  producing  intense  inflammation,  necrosis,  and  suppuration  in  the  absence  of 
bacteria. 

Neurine,  C5H13NO,  is  a  base  which  has  been  obtained  by  boiling  protagon 
with  baryta,  and  has  been  formed  by  synthetical  processes.  It  also  occurs, 
however,  frequently  in  decomposing  meat.  It  is  exceedingly  poisonous,  even 
in  small  doses.  Atropine  possesses  a  strong  antagonistic  action  toward  neurine, 
and  the  injection  of  even  a  small  quantity  is  sufficient  to  dispel  the  symptoms 
of  poisoning  by  neurine. 

Choline,  C5H15NO2,  has  been  found  in  animal  tissues,  in  a  number  of  plants 
(hops,  ergot,  Indian  hemp,  white  mustard,  etc.),  and  in  putrid  matters.  It  is 
much  less  poisonous  than  neurine. 

Mytilotoxine,  C6H15NO2,  is  the  poison  found  in  poisonous  mussels.  It  has  a 
strong  paralysis-producing  action,  resembling  curara  in  that  respect. 


ALKALOIDS.  621 

Typhotoxine,  C7H17NO2,  is  looked  upon  as  the  specific  toxic  product  of  the 
activity  of  Koch-Eberth's  typhoid  bacillus.  The  poison  throws  animals  into  a 
paralytic  or  lethargic  condition,  so  that  they  lose  control  over  the  muscles  and 
fall  down  helpless.  Simultaneously  frequent  diarrhoeic  evacuations  take  place, 
and  death  follows  in  from  one  to  two  days. 

Tetanine,  C13H30N2O4,  has  been  obtained  from  cultures  of  tetanus  microbes, 
from  the  amputated  arm  of  a  tetanus  patient,  and  from  the  brain  and  nerve 
tissues  of  persons  who  died  from  tetanus.  It  produces  in  animals  the  symp- 
toms characteristic  of  tetanus,  such  as  tonic  and  clonic  convulsions.  While 
mice  and  rabbits  are  strongly  affected  by  tetanine,  dogs  and  horses  seem  to  be 
but  slightly  susceptible  to  its  action. 

Mydatoxine,  C6H13NO2,  has  been  obtained  from  human  internal  organs  which 
were  kept  for  four  months  at  a  temperature  varying  from — 9°  to  -f  5°C.  (16° 
to  41°  F.).  It  is  an  alkaline  syrup,  which  does  not  possess  strong  toxic 
properties. 

Tyrotoxlcon.  The  composition  of  this  highly  poisonous  ptomaine  has  not 
been  established  yet.  It  has  been  found  in  decomposing  milk,  in  poisonous 
cheese,  ice-cream,  and  cream-puffs. 

Spasmotoxine.  Composition  yet  unknown.  Obtained  from  cultures  of  the 
tetanus-germ  on  beef-broth.  Produces  violent  convulsions. 

Leucomaines.  The  basic  substances  formed  in  the  living  tissues 
by  retrograde  metamorphosis,  during  normal  life,  are  known  as  leuco- 
maines,  in  contradistinction  to  the  ptomaines,  or  basic  products  of 
putrefaction.  To  the  group  of  leucomaines  belong  many  substances 
known  long  ago,  such  as  creatine,  creatinine,  xanthine,  guanine,  and 
others.  Most  of  these  bodies  are  non-poisonous,  but  some  have  been 
discovered  of  late,  possessing  strong  poisonous  properties.  The 
accumulation  of  these  substances  in  the  body,  because  of  incomplete 
excretion  or  oxidation,  produces  auto-intoxication.  The  more  impor- 
tant leucomaines  will  be  mentioned  in  the  physiological  part. 

QUESTIONS.— State  the  general  physical  and  chemical  properties  of  alka- 
loids. Give  a  general  method  for  the  extraction  and  separation  of  alkaloids 
from  vegetables.  Mention  the  chief  constituents  of  opium.  Mention  the  prop- 
erties of  morphine  and  its  salts;  give  tests  for  them.  Mention  the  principal 
alkaloids  found  in  cinchona  bark.  State  the  physical  and  chemical  properties 
of  quinine  and  cinchonine.  Which  of  their  salts  are  official,  and  by  what  tests 
may  these  alkaloids  be  recognized  and  distinguished  from  each  other?  Give 
tests  for  strychnine,  brucine,  atropine,  and  veratrine.  What  is  the  chemical 
relationship  between  xanthine,  caffeine,  and  theobromine  ?  Mention  proper- 
ties of,  and  give  tests  for,  cocaine.  Mention  the  characteristic  physical,  chem- 
ical, and  physiological  properties  of  ptomaines. 


VII. 
PHYSIOLOGICAL  CHEMISTRY. 


53.  PROTEINS. 

General  remarks.  Physiological  chemistry  is  that  part  of  chem- 
istry which  has  more  especially  for  its  object  the  various  chemical 
changes  which  take  place  in  the  living  organism  of  either  plants  or 
animals.  It  considers  the  chemical  nature  of  the  different  substances 
used  as  "food/'  follows  up  the  changes  which  this  food  undergoes 
during  its  absorption  and  assimilation  in  the  organism,  and  treats, 
finally,  of  the  products  eliminated  by  it.  The  chemical  changes  tak- 
ing place  in  the  organism  are  either  normal  (in  health)  or  abnormal 
(in  disease).  The  abnormal  products  formed  under  abnormal  condi- 
tions are  generally  termed  "  pathological "  products. 

Of  the  three  classes  of  organic  compounds,  viz.,  fats,  carbohydrates, 
and  proteins,  from  which  our  food-supply  is  chiefly  derived,  the  first 
two  have  been  considered  in  the  part  on  Organic  Chemistry,  while  the 
study  of  proteins  is  taken  up  in  this  chapter. 

Occurrence  in  nature.  Proteins  form  the  chief  part  of  the  solid 
and  liquid  constituents  of  the  animal  body ;  they  occur  in  blood, 
tissues,  muscles,  nerves,  glands,  and  all  other  organs ;  they  are  also 
found  in  small  quantities  in  nearly  every  part  of  plants,  and  in  larger 
quantities  in  many  seeds.  They  have  never  yet  been  formed  by  arti- 
ficial means,  but  are  almost  exclusively  products  of  vegetable  and 
animal  life. 

General  properties.  The  word  protein  (formerly  proteid)  re- 
fers to  a  member  of  that  group  of  substances  which  consist,  so 
far  as  is  known  at  present,  essentially  of  combinations  of  a-amino- 

623 


624  PHYSIOLOGICAL   CHEMISTRY. 

acids l  and  their  derivatives,  e.  g.y  a-amino-acetic  acid  or  glycocoll ; 
a-amino-propionic  acid  or  alanine  ;  phenyl-a-amino-propionic  acid  or 
phenylalanine ;  guanidine-amino- valeric  acid  or  arginine,  etc.,  and  are, 
therefore,  essentially  polypeptides.  The  various  proteins  resemble  one 
another  closely  in  their  properties.  Their  composition  is  so  complex 
that,  as  yet,  no  chemical  formula  has  been  assigned  to  them  with  any  cer- 
tainty; they  all  contain  carbon,  hydrogen,  oxygen,  and  nitrogen;  most 
contain  sulphur,  several  phosphorus,  and  some  iron.  Various  other 
metallic  and  non-metallic  elements  have  been  found  in  certain  proteins. 

Nearly  all  proteins  are  amorphous,  non-diffusible,  colorless,  odor- 
less, nearly  tasteless,  and  non-volatile.  When  heated  under  such 
conditions  that  the  volatile  products  formed  are  not  burnt  at  all,  or 
only  partially,  a  disagreeable  odor  is  noticed,  due  chiefly  to  ammonia 
derivatives.  Proteins  vary  in  solubility ;  all  are  optically  active, 
most  of  them  being  laevorotatory,  while  haemoglobin  and  the  nucleo- 
proteins  are  dextrorotatory.  Proteins  are  distinguished  by  the  ease 
with  which  they  undergo  chemical  change  under  the  influence  of 
reagents,  ferments,  or  variations  in  temperature ;  they  all  undergo 
the  process  of  putrefaction,  which  has  been  considered  in  Chapter  41. 

By  boiling  with  dilute  acids  or  alkalies,  and  also  by  the  action  of 
certain  enzymes,  the  proteins  undergo  hydrolytic  cleavage,  forming 
many  simpler  compounds.  (The  terms  hydrolytic  cleavage  and 
hydrolysis  -will  be  explained  more  fully  later  on  ;  they  refer  to  a 
splitting  up  of  complex  molecules,  while  water  or  its  constituents  are 
taken  up  at  the  same  time.) 

Classification.  The  classification  here  used  is  the  one  which  has 
been  adopted  by  the  American  Society  of  Biological  Chemists  and 
the  American  Physiological  Society,  and  is  as  follows : 

I.  SIMPLE  PROTEINS. — a,  Albumins;  b,  Globulins;  c,  Glutelins ; 
d,  Prolamines,  or  Alcohol-soluble  proteins;  e,  Albuminoids;  f,  His- 
tones  ;  g,  Protamines. 

II.  CONJUGATED  PROTEINS. — a,  Nucleoproteins  ;  b,  Gtycoproteins  ; 
c,  Phosphoproteins  ;  d,  Haemoglobins ;  e,  Lecithoproteins. 

III.  DERIVED  PROTEINS  : 

1.  Primary  protein  derivatives:  a,  Proteans ;  b,  Metaproteins ;  c, 
Coagulated  proteins.  2.  Secondary  protein  derivatives  :  a,  Proteases; 
b,  Peptones;  c,  Peptides. 

1  Greek  letters  are,  in  some  cases,  used  to  indicate  the  position  of  substituting  groups  in  a 
molecule.  In  organic  acids,  the  carbon  atom  next  to  the  carboxyl  group  (COOH)  is  designated 
by  a,  the  next  one  by  /3,  the  next  one  by  y,  etc.  Thus,  lactic  acid  is  a-hydroxy-propionic 
acid,  CH3.CHOH.COOH;  alanine  is  a-amino-propionic  acid,  CH3.CHNH2.COOH;  glycocoll  is 
a-amino-acetic  acid,  CH2NH2.COOH ;  hydracrylic  acid  is  £-hydroxy-propionic  acid,  CH2OH.- 
CH2COOH. 


PROTEINS.  625 

I.  Simple  proteins. 

These  are  protein  substances  which  yield  only  a-amino-acids  or 
their  derivatives  by  hydrolysis. 

The  simple  proteins  occur  in  all  animal  and  vegetable  organisms. 
In  the  animal  body  they  are  the  most  prominent  solid  constituents 
of  the  muscles,  glands,  and  blood-serum,  and  are  found  to  a  greater 
or  less  extent  in  all  tissues,  secretions,  and  excretions.  The  percent- 
age composition  of  simple  proteins  is  as  follows  : 

Carbon 50.0  to  55.0  per  cent. 

Hydrogen 6.5  "    7.3       " 

Nitrogen 15.0  "  18.0       " 

Oxygen 21.0  "  24.0 

Sulphur 0.3  "    2.5       " 

A  few  simple  proteins  contain  phosphorus  to  the  extent  of  0.42— 
0.85  per  cent.,  and  a  few  contain  also  a  trace  of  iron. 

The  nitrogen  of  proteins  is  split  off  in  four  forms,  viz.,  as  ammo- 
nia, as  diamino-acids,  as  monami no-acids,  and  as  a  guanidine  residue. 
Part  of  the  nitrogen  is  easily  split  off  as  ammonia  by  the  action  of 
alkalies. 

By  boiling  proteins  with  alkalies,  part  of  the  sulphur  is  split  off 
as  sulphide,  while  the  remainder  can  be  obtained  as  sulphate,  after 
fusing  the  residue  with  potassium  nitrate  and  sodium  carbonate.  As 
about  one-half  of  the  total  sulphur  present  is  obtained  by  each  opera- 
tion, it  is  assumed  that  there  are  at  least  two  atoms  of  sulphur  in  the 
protein  molecule. 

When  acted  upon  by  enzymes  or  other  hydrolytic  agents,  the 
simple  proteins  form  first  proteins  of  lower  molecular  weight,  which 
are  diffusible  and  not  coagulated  by  heat.  By  the  prolonged  action 
of  certain  ferments  (trypsin,  bacteria,  etc.),  or  by  long  boiling  with 
acids,  they  give  rise  to  the  formation  of  amino-acids  (tyrosine,  leucine, 
aspartic,  and  glutamic  acids),  of  the  hexone  bases  (lysine,  arginine, 
histidine),  and  a  number  of  undefined  bodies. 

In  solubility  the  simple  proteins  vary ;  some  are  soluble  in  water, 
others  only  in  water  containing  either  acids,  alkalies,  or  certain 
neutral  salts,  while  yet  others  are  insoluble.  The  soluble  proteins 
are  converted  into  insoluble  modifications  by  the  action  of  heat  or 
certain  reagents.  This  change  is  called  coagulation,  and  is  distin- 
guished from  precipitation  by  the  fact  that  proteins  when  once  coagu- 
lated cannot  return  to  their  original  condition.  The  temperature  at 
which  coagulation  takes  place  depends  on  the  nature  of  the  protein 
present,  the  reaction  of  the  solution,  and  the  presence  of  neutral  salts. 
40 


626  PHYSIOLOGICAL  CHEMISTRY. 

An  alkaline  solution  of  a  protein  will  not  coagulate  on  boiling ;  a  neutral 
solution  will  do  so  partially  ;  a  solution  showing  an  acid  reaction  will  be 
coagulated  completely  on  boiling,  provided  the  quantity  of  neutral  salt  present 
be  not  too  small,  and  the  protein  solution  not  too  dilute. 


Tests  for  simple  proteins. 

a.  Coagulation  or  precipitation  tests. 

(Use  a  solution  made  by  dissolving  white  of  an  egg  in  about  10  parts  of  a 
2  per  cent,  sodium  chloride  solution.) 

1.  Heat  test.     To  5  c.c.  of   protein  solution  add  a  few  drops  of 
dilute  acetic  acid,  and  heat.     The  protein  is  completely  coagulated. 

2.  Heller's  test.     Place  1  c.c.  of  nitric  acid  in  a  test-tube,  and  allow 
a  few  c.c.  of  protein  solution  to  flow  down  the  side  of  the  tube,  taking 
care  that  the  liquids  do  not  mix.     A  white,  opaque  ring  of  coagu- 
lated   protein  forms   at    the    line    of  junction.     (Strong    sulphuric, 
hydrochloric,  and    metaphosphoric  acids    coagulate  proteins  in    the 
same  way.) 

3.  To  5  c.c.  of  protein  solution   add  solution  of  cupric  sulphate ; 
repeat  with  solutions  of  mercuric  chloride,  lead  acetate,  and  silver 
nitrate.     In   all    cases    coagulation    takes   place.     (These   reactions 
explain  the  use  of  proteins,  such  as  the  white  of  egg,  as  antidotes  in 
cases  of  poisoning  by  metallic  compounds.) 

4.  To  5  c.c.  of  protein  solution  add  a  few  drops  of  acetic  acid  and 
some  potassium  ferrocyanide  solution  ;  coagulation  takes  place. 

5.  Saturate   10  c.c.  of  protein  solution  with  ammonium  sulphate  ; 
all  proteins  are  precipitated  except  peptones. 

6.  Solutions  of   picric,  trichloracetic,  phosphotungstic,   phospho- 
molybdic,  tannic,  taurocholic,  and  nucleic  acids,  potassium  mercuric 
iodide,  alcohol,  all  precipitate  proteins  under  special  conditions. 

b.  Color  tests. 
(Use  any  dry  protein.) 

1.  Xanthoproteic  reaction.     Heat  a  small  quantity  of  protein  with 
concentrated  nitric  acid  ;  the  protein,  or  the  solution,  turns  yellow. 
Allow  it  to  cool,  and  add  an  excess  of  ammonia :  the  color  changes 
to  orange.     (Plate  VIII.,  1.) 

This  reaction  is  due  to  the  presence  of  the  tyrosine  and  the  trypto- 
phane  radicals  in  the  protein  molecule. 

2.  Milton's  reaction.     Pour  a  few  c.c.  of  water  on  a  small  quantity 
of  protein  ;  add  1  c.c.  of  Millon's  reagent,  and  boil :  a  purple-red 
color  develops.     (Millon's  reagent  is  made  by  dissolving  10  grammes 


PROTEINS.  627 

of  mercury  in  the  same  weight  of  pure  nitric  acid,  and  adding  to  the 
cool  solution  2  volumes  of  water.)  This  reaction  is  given  by  tyrosine. 

3.  Biuret  reaction.     Boil  a  small  quantity  of  protein  with  5  c.c. 
of  solution  of  sodium  hydroxide,  and  after  cooling  add  one  or  two 
drops  of  dilute  solution  of  cupric  sulphate :  a  violet  to  pink  color  is 
obtained,  according  to  the  amount  of  copper  solution  and  the  nature 
of  the  protein.     (Plate  VIII.,  2.)     (It  may  be  necessary  to  heat  the 
solution  before  a  distinct  color  appears.) 

This  reaction  is  given  by  biuret,  hence  its  name. 

Boil  a  small  quantity  of  protein  in  a  test-tube  with  absolute  alcohol ;  filter, 
wash  with  absolute  alcohol,  then  with  ether,  and  use  the  dry  material  for  the 
following  tests. 

4.  Adamkieivicz's  reaction.     Dissolve  a  small  quantity  of  the  pro- 
tein by  boiling  with  glacial  acetic  acid.     Allow  to  cool,  and,  holding 
the  test-tube  in  an  inclined  position,  let  2  c.c.  of  concentrated  sul- 
phuric   acid  flow  down  the  side  of  the  tube.      A  violet  or  purple 
color  develops  where  the  liquids  meet. 

This  reaction  is  due  to  tryptophane,  and  is  produced  by  an  impurity 
in  the  acetic  acid  used,  i.  e.,  glyoxylic  acid,  CHO — COOH  (Hopkins- 
Cole).  A  few  drops  of  a  dilute  solution  of  glyoxylic  acid  can  be 
added  when  the  acetic  acid  used  fails  to  give  a  positive  test. 

5.  Lieberman's  reaction.     To  some  of  the  dry  protein  add  concen- 
trated hydrochloric  acid  :   the  protein  turns  deep  blue  to  violet.     On 
standing,  the  color  fades.     Probably  due  to  tryptophane. 

Many  of  the  above  color-reactions  will  be  given  by  the  cleavage-products 
of  proteins,  and  by  various  other  substances,  but  the  proteins  alone  will 
respond  to  all  of  the  five  tests. 

(a)  Albumins.     These  substances  are  soluble  in  water  and  are  pre- 
cipitated from  their  aqueous  solution  by  large  quantities  of  mineral 
acids  and  by  saturation  of  their  solution  with  ammonium  sulphate. 
In  a  solution  containing  1  per  cent,  of  neutral  salt  they  are  coagulated 
between  60°  and  75°  C.  (140°  and  167°  F.). 

They  include  ovalbumin  (white  of  egg) ;  serum-albumin  of  blood- 
serum  and  serous  fluids ;  lactalbumin  of  milk  ;  and  vegetable  albumins. 

(b)  Globulins.     These  compounds  are  insoluble  in  water,  but  dis- 
solve in  water  containing  from  0.5  to  1  per  cent,  of  some  neutral  salt. 
The  solution  coagulates  on  heating,  is  precipitated  by  saturation  with 
magnesium  sulphate  or  sodium  chloride,  and  by  the  addition  of  an 
equal  volume  of  saturated  solution  of  ammonium  sulphate.   Globulins 
are  precipitated  if  the  salt  be  removed  from  their  solution  by  dialysis. 


628  PHYSIOLOGICAL   CHEMISTRY. 

Serum-  or  para-globulin  of  blood,  lacto-globulin  of  milk,  and 
fibrinogen  are  globulins. 

(c)  Glutelins  are  simple  proteins  insoluble  in  all  neutral  solvents, 
but  readily  soluble  in  very  dilute  acids  and  alkalies.     They  occur  in 
abundance  in  the  seeds  of  cereals. 

(d)  Prolamines  or  alcohol-soluble  proteins.      These  are  soluble 
in  70  to  80  per  cent,  alcohol,  and  in  dilute  acids  and  alkalies,  but  in- 
soluble in  water,  absolute  alcohol,  and  other  neutral  solvents.    Similar 
to  glutelins,  they  are  found  chiefly  in  the  vegetable  kingdom.     For 
instance,  zein  is  found  in  maize,  gliadin  in  wheat,  hordein  in  barley, 
etc. 

(e)  Albuminoids.     Simple  proteins  which  possess  essentially  the 
same  chemical  structure  as  the  other  proteins,  but  are  characterized 
by  great  insolubility  in  all  neutral  solvents.     They  occur  chiefly  as 
constituents  of  the   skeleton,  of  the  skin   and   its  appendages,  and 
exist,  as  a  rule,   in  an    insoluble    condition.     To   the   albuminoids 
belong :  Keratins,  elastin,  collagen,  and  a  few  other  substances. 

Keratins  occur  as  the  principal  constituents  of  the  horny  por- 
tion of  the  skin  and  its  appendages.  A  special  keratin,  neurokeratin, 
is  found  in  the  nervous  system.  The  keratins  contain  proportion- 
ately more  sulphur  than  other  proteins,  part  of  it  in  very  loose  com- 
bination. The  darkening  of  the  hair  by  the  use  of  a  lead  comb, 
forming  black  lead  sulphide,  is  due  to  the  action  of  this  sulphur. 
The  products  of  deep  cleavage  of  the  keratins  are  the  same  as  those 
of  the  proteins,  but  with  relatively  greater  quantities  of  the  sul- 
phurized products,  mainly  in  the  form  of  cystine. 

Keratins  dissolve  slowly  in  cold  caustic  alkalies,  more  rapidly  on 
heating.  They  are  insoluble  in  water,  alcohol,  ether,  and  in  gastric 
and  pancreatic  juices.  They  give  the  xanthoproteic,  biuret,  and 
Millon's  reactions. 

Elastin  occurs  in  the  connective  tissue,  particularly  in  yellow 
elastic  fiber;  it  contains  very  little  sulphur  (less  than  0.5  per  cent.), 
and  yields  on  deep  cleavage  the  same  products  as  simple  proteins, 
giving,  however,  glycocoll,  little  glutamic  acid,  and  no  aspartic  acid. 

Elastin  is  insoluble  in  water  and  in  cold  solutions  of  caustic  alka- 
lies ;  it  dissolves  slowly  in  alkalies  on  boiling  and  in  cold  sulphuric 
acid ;  it  is  easily  dissolved  by  warm  nitric  acid,  as  also  by  the  action 
of  proteolytic  enzymes.  It  shows  the  same  color-reactions  as  the 
keratins. 

Collagen  occurs  in  the  fibre  of  connective  tissue.  Ossein,  the 
chief  organic  constituent  of  bone,  is  a  collagen;  and  chondrin,  a 


PROTEINS.  629 

constituent  of  cartilage,  is  collagen  mixed  with  a  small  quantity  of 
other  material. 

On  boiling  with  water  (more  readily  with  acidified  water)  collagen 
is  converted  into  gelatin,  while  the  latter,  when  heated  to  130°  C. 
(266°  F.),  is  converted  into  collagen.  (Collagen  may,  therefore,  be 
considered  an  anhydride  of  gelatin.) 

Gelatin  yields  no  tryptophane,  no  tyrosine,  and  contains  a  rather 
small  percentage  of  sulphur. 

Reticulin,  occurring  in  reticular  tissue,  and  skelatins,  forming  the  skeletal 
tissues  of  invertebrates,  are  classed  with  the  albuminoids. 

(/)  Histones.  Soluble  in  water  and  insoluble  in  very  dilute 
ammonia,  and,  in  the  absence  of  ammonium  salts,  insoluble  even  in 
an  excess  of  ammonia  ;  yield  precipitates  with  solutions  of  other  pro- 
teins. On  hydrolysis  they  yield  a  large  number  of  amino-acids, 
among  which  the  basic  ones  predominate,  such  as  arginine  and  histi- 
dine,  while  others  of  them  are  absent  (cystine,  tyrosine). 

(g)  Protamines.  Simpler  polypeptides  than  the  proteins  included 
in  the  preceding  groups.  They  are  soluble  in  water,  uncoagulable  by 
heat,  have  the  property  of  precipitating  aqueous  solutions  of  other 
proteins,  possess  strong  basic  properties,  and  form  stable  salts  with 
strong  mineral  acids.  They  are  the  simplest  natural  proteins. 

II.  Conjugated  proteins. 

Substances  which  contain  the  protein  molecule  united  to  some 
other  molecule  or  molecules  otherwise  than  as  a  salt. 

(a)  Nucleoproteins.  These  are  compounds  of  one  or  more  pro- 
tein molecules  with  nucleic  acid.  They  occur  chiefly  in  the  cell 
nuclei,  but  are  found  also  in  the  protoplasm.  Nucleoproteins  yield, 
on  digestion  with  pepsin,  a  simple  protein,  usually  a  histone  or  a  pro- 
tamine,  and  nuclein.  Nuclein  is  generally  but  not  always  resistant 
to  peptic  digestion.  On  treatment  with  caustic  alkali  it  is  split  into 
protein  and  nucleic  acid,  which  is  the  important  portion  of  the 
nucleoproteins.  This  nucleic  acid  consists  of  a  carbohydrate  group 
linking  together  nitrogenous  bases  and  phosphoric  acid.  As  there 
are  many  different  nucleic  acids  these  constituent  groups  vary  within 
certain  limits.  The  carbohydrates  may  be  pentose  or  hexose.  The 
nitrogenous  bases  may  be  one  or  more  purine  bodies  (guanine,  adenine, 
etc.)  or  pyrimidine  derivatives  (thymine,  cytosine,  uracil).  The  phos- 
phoric acid  is  said  to  be  metaphosphoric  acid.  The  purine  bodies  in 
nucleins  are  the  origin  of  the  uric  acid  of  human  urine. 


630  PHYSIOLOGICAL   CHEMISTRY. 

The  nucleoproteins  give  all  the  color  reactions,  are  soluble  in  water  con- 
taining a  small  quantity  of  alkali,  and  are  precipitated  from  this  solution  by 
acetic  acid.  "They  are  dextro-rotatory. 

(6)  Glycoproteins.  Compounds  of  the  protein  molecule,  with  a 
substance  or  substances  containing  a  carbohydrate  group  other  than  a 
nucleic  acid.  This  carbohydrate  group  is  capable  of  reducing  cupric 
oxide.  Several  groups  of  glycoproteins  are  differentiated  as  follows  : 

Mucins  are  secreted  by  the  larger  mucous  glands  of  the  body, 
by  certain  mucous  membranes,  and  are  found  also  in  the  connective 
tissue  and  umbilical  cord.  The  mucins  are  soluble  in  water  con- 
taining a  little  alkali.  The  solution  is  mucilaginous,  and  with  acetic 
acid  gives  a  precipitate  insoluble  in  an  excess  of  the  acid.  This 
precipitate  is  not  formed  in  the  presence  of  5  to  10  per  cent,  of 
sodium  chloride.  The  solution  is  not  coagulated  by  heat  nor  pre- 
cipitated by  potassium  ferrocyanide.  An  acid  solution  containing 
salts  is  precipitated  by  tannic  acid,  and  a  similar  neutral  solution  by 
alcohol,  as  also  by  salts  of  heavy  metals.  Mucins  when  pure  are 
acid  in  reaction,  and  give  the  protein  color-reactions. 

Mucoids  are  certain  mucin-like  substances,  such  as  colloid  and 
ovomucoid,  and  differing  from  the  mucins  in  solubility  and  certain 
other  physical  properties.  The  mucoids  are  not  precipitated  by 
acetic  acid. 

Chondroproteins  (chondromucoid,  amyloid)  yield  chondroitin- 
snlphuric  acid  as  one  of  the  decomposition-products.  This  latter 
has  the  power  to  reduce  cupric  oxide  and  to  precipitate  proteins ;  it 
is  sometimes  found  in  the  urine. 

Chondromucoid  occurs  in  cartilage;  it  resembles  the  mucins  in 
solubility  and  other  properties. 

Amyloid  occurs  pathologically  as  an  infiltration  in  the  spleen,  liver, 
kidneys,  and  other  organs.  Amyloid  is  insoluble  without  decomposi- 
tion. It  gives  the  biuret,  xanthoproteic,  Millon's,  and  Adamkiewicz's 
reactions. 

The  reactions  with  the  following  coloring-matters  are  characteristic  for 
amyloid :  It  is  colored  red  by  aniline-green  ;  also  red  by  methyl-aniline  iodide, 
especially  after  the  addition  of  acetic  acid ;  violet  or  blue  by  iodine  and  sul- 
phuric acid  ;  and  reddish-brown  or  violet  by  iodine. 

(c)  Phosphoprotein.  Compounds  of  the  protein  molecule  with 
some,  as  yet  undefined,  phosphorus-containing  substance  other  than 
a  nucleic  acid  or  lecithin.  Caseinogen,  the  principal  protein  con- 
stituent of  milk,  belongs  to  this  group. 


PROTEINS.  631 

(d)  Haemoglobins.     Compounds   of  the   protein    molecule,  with 
hseinatin  or  some  similar  substance.    Haemoglobins  form  the  coloring- 
matters  of  the  blood.     On  hydrolysis  they  yield  a  simple  protein  and 
a  substance  called  haemochromogen,  which  contains  iron  and  is  read- 
ily oxidized  to  hsematin.     (Further  discussion  under  Blood.) 

(e)  Lecithoproteins.     Compounds  of  the  protein   molecule  with 
lecithins,  which  will  be  considered  later.     (See  Index  for  lecithins.) 

III.  Derived  proteins. 

These  substances  are  derivatives  of  proteins,  and  are  obtained  from 
them  by  hydrolytic  changes  of  various  kinds,  e.  g.,  through  the  action 
of  acids,  alkalies,  heat,  or  enzymes. 

1.  Primary  protein  derivatives. 

Derivatives  of  the  protein  molecule  apparently  formed  through 
hydrolytic  changes  which  involve  only  slight  alterations  of  the  pro- 
tein molecule. 

(a)  Proteans.  Insoluble  products  which  apparently  result  from 
the  incipient  action  of  water,  very  dilute  acids,  or  enzymes  on  pro- 
teins originally  soluble. 

(6)  Metaproteins.  Products  of  the  further  action  of  acids  and 
alkalies,  whereby  the  molecule  is  so  far  altered  as  to  form  products 
soluble  in  very  weak  acids  and  alkalies,  but  insoluble  in  neutral 
fluids.  The  two  principal  metaproteins  are  the  alkali  metaprotein  or 
alkali  albuminate  and  the  acid  metaprotein  or  acid  albuminate. 

Alkali  metaprotein  is  formed  when  native  proteins  are  acted  upon 
by  alkalies  to  such  an  extent  that  part  of  the  nitrogen,  and  occasion- 
ally sulphur  also,  is  eliminated  from  the  molecule.  The  change 
takes  place  slowly  at  the  ordinary  temperature,  more  rapidly  on 
heating. 

Acid  metaprotein  is  obtained  by  digesting  a  native  protein  with 
dilute  acid. 

Alkali  and  acid  metaproteins  (album inates)  have  certain  properties 
in  common.  Both  are  insoluble  in  water  or  neutral  salt  solution,  but 
easily  soluble  in  the  presence  of  a  small  amount  of  either  an  acid  or 
an  alkali.  The  solution  does  not  coagulate  on  boiling,  but  is  com- 
pletely precipitated  when  neutralized.  A  solution  in  dilute  acid  is 
also  precipitated  by  saturation  with  magnesium  sulphate,  ammonium 
sulphate,  or  sodium  chloride,  while  a  solution  in  alkali  is  not  precipi- 
tated by  similar  treatment.  Although  agreeing  in  many  reactions, 
alkali  and  acid  metaproteins  are  essentially  different.  Thus  the 


632  PHYSIOLOGICAL   CHEMISTRY. 

alkali  metaproteins  have  decided  acid  properties,  as  can  be  shown  by 
the  fact  that  on  the  addition  of  calcium  carbonate  they  dissolve  in 
water  with  the  liberation  of  carbon  dioxide,  a  property  not  possessed 
by  acid  metaproteins. 

As  part  of  the  nitrogen  is  eliminated  during  the  formation  of  alkali 
metaproteins,  the  latter  cannot  be  converted  into  acid  metaproteins  by 
treatment  with  acids ;  the  reverse  change,  however,  may  be  brought 
about. 

(c)  Coagulated  proteins.  Insoluble  products,  which  result  from 
the  action  of  heat  on  their  solutions,  or  from  the  action  of  alcohols  on 
the  protein.  The  nature  of  the  process  of  coagulation  is  unknown  ; 
the  result  is  the  formation  of  protein  substances  insoluble  without 
decomposition.  In  the  liver  and  other  glands  coagulated  proteins 
have  been  found.  Hard-boiled  white  of  egg  and  fibrin  are  coagu- 
lated proteins. 

The  temperature  of  coagulation  is  constant  for  any  certain  protein  ; 
it  is,  however,  considerably  modified  by  the  presence  or  absence  of 
acids,  alkalies,  and  salts  in  the  solution.  Fractional  coagulation  by 
gradual  heating  of  a  solution  of  several  proteins  aifords  a  rough  means 
of  separation. 

2.  Secondary  protein  derivatives. 

Products  of  the  further  hydrolytic  cleavage  of  the  protein  mole- 
cule by  acids,  alkalies,  superheated  steam,  or  enzymes. 

(a)  Proteoses.  Soluble  in  water,  uncoagulated  by  heat,  and  pre- 
cipitated by  saturating  their  solutions  with  ammonium  sulphate  or 
zinc  sulphate. 

Primary  proteoses  (protalbumoses)  are  precipitated  by  one-half 
saturation  with  ammonium  sulphate. 

Secondary  proteoses  (deutero-albumoses)  are  precipitated  by  com- 
plete saturation  with  ammonium  sulphate. 

There  are  several  subdivisions  of  primary  and  secondary  proteoses, 
viz.,  hetero-proteoses,  dysproteoses,  the  different  properties  of  which 
are  not  definite. 

(6)  Peptones.  Soluble  in  water,  uncoagulated  by  heat,  and  not 
precipitated  by  saturating  their  solutions  with  ammonium  sulphate. 
They  are  the  result  of  the  digestion  of  proteins ;  their  solutions  in 
water  are  readily  diffusible.  The  peptones  are  divided  into  anti-pep- 
tones, hemi-peptones,  and  ampho-peptones.  Here,  again,  the  proper- 
ties of  the  different  classes  are  not  definite. 

The  proteoses  and  peptones  give  a  biuret  reaction  showing  more 
red  color  than  the  natural  proteins. 


PROTEINS.  633 

(c)  Peptides.  Definitely  characterized  combinations  of  two  or  more 
ami  no -acids,  the  carboxyl  group  of  one  being  united  with  the  amino 
group  of  the  other  with  the  elimination  of  a  molecule  of  water.  The 
peptones  are  peptides  or  mixtures  of  peptides,  the  latter  term  being 
at  present  used  to  designate  those  of  definite  structure,  such  as  poly- 
peptides,  dipeptides,  etc. 

Products  of  proteolysis. 

Proteolysis  is  the  change  effected  in  proteins  during  their  diges- 
tion, and  is  brought  about  by  the  action  of  bodies  termed  proteolytic 
agents,  or  enzymes.  The  products  formed  vary  in  quantity  and  com- 
position with  the  nature  of  the  proteins  and  enzymes,  and  depend 
also  on  the  condition  under  which  the  changes  take  place.  While 
the  compounds  grouped  together  as  proteins  differ  widely  in  their 
properties,  yet  the  end-products  of  any  proteolysis  will  be  comprised 
in  a  few  amino-acids  and  nitrogenous  bases.  This  would  indicate  that 
there  exists  a  close  relation  between  the  different  proteins,  the  differ- 
ence being  due  more  to  the  atomic  arrangement  within  the  molecule 
than  to  the  quality  and  quantity  of  the  elements  present  in  protein 
molecules. 

These  decomposition  products  of  proteins  are  : 

(1)  Monamino-acids : 

Glycocoll  (amino-acetic  acid),  CH2.NH2.CO2H. 

Alanine  (aminopropionic  acid),  C2H4.NH2.CO2H. 

Valine  (amino-iso-valeric  acid),  C4H8.NH2.CO2H. 

Aspartic  acid  (aminosuccinic  acid),  C2H3.NH2.(CO2H)2. 

Glutamic  acid  (amino-pyrotartaric  acid),  C3H5.NH2.(CO2H)2. 

Phenylalanine  (phenyl-amino-propionic  acid),  C6H5.C2H3.NH2.CO2H. 

Iso-leucine  (amino-methyl-ethyl-propionic  acid),  C6H10.NH2.CO2H. 

Leucine  (amino-caproic  acid),  C5H,0.NH2.CO2H. 

Serine  (amino-oxypropionic  acid),  C2H3(OH).NH2.CO2H. 

Proline  (pyrrolidine-carboxylic  acid),  C4H7.NH.CO2H. 

Oxyproline  (oxypyrrolidine-carboxylic  acid),  C4H7O.NH.CO2H. 

Tryptophane  (indol-amino-propionic  acid),  CU.H]2N2O2. 

Cystine  (disulphide  of  aminothio-propionic  acid  (cysteine),  (C2H3S.NH3.- 

C02H)2. 
Tyrosine  (oxyphenyl-amino-propionic  acid),  C8H8O.NH2.CO2H. 

(2)  Diamino-acids  (hexone  bases)  : 

Arginine  (guanidine-aminovaleric  acid),  C6H,4N4O2. 
Histidine  (amino-iimdazol-propionic  acid),  C6H9N3O2. 
Lysine  (diamino-caproic  acid),  C6H14N2O2. 

An  enormous  amount  of  work  is  being  done  in  the  attempt  to  solve 
the  protein  molecule  by  studying  these  substances  (proteoses,  peptones, 


634  PHYSIOLOGICAL   CHEMISTRY. 

peptides,  ammo-acids)  obtained  by  proteolysis.  They  are  successively 
simpler,  more  soluble,  and  more  diffusible  as  the  proteolysis  proceeds. 
The  constitution  of  many  of  these  simpler  decomposition  products  has 
now  been  well  substantiated  (amino-acids).  It  has  been  found  pos- 
sible to  make  a  beginning  in  the  synthesis  of  protein  by  forming  com- 
binations of  amino-acids,  linking  the  carboxyl  group  of  one  to  the 
amino  group  of  another,  with  the  elimination  of  a  molecule  of  water. 
This  procedure  can  be  repeated,  and  substances  have  been  formed 
containing  thirty-six  or  more  amino-acid  molecules.  These  substances 
are  apparently  entirely  analogous  to  the  peptides  derived  from  the 
proteins,  as  some  of  them  give  a  biuret  test,  are  acted  upon  by  prote- 
olytic  enzymes  (erepsin),  and  have  other  common  properties.  It  is 
probable,  therefore,  that  this  grouping  is  one  of  the  many  forms  of 
combination  that  must  be  present  in  the  protein  molecule.  While  all 
of  these  amino-acids  have  been  found  in  protein,  they  are  not  neces- 
sarily all  present  in  any  one  protein,  and  in  different  proteins  they 
are  present  in  markedly  different  proportions.  Experimental  work 
is  beginning  only  now  to  show  the  significance  of  these  differences 
in  the  proteins.  The  molecular  weights  of  the  proteins  cannot  be 
determined  by  any  known  methods,  and  the  actual  structural  consti- 
tution is  entirely  unknown. 

As  leucine  and  tyrosine  are  readily  isolated  (see  Pancreatic  Diges- 
tion), their  more  important  properties  are  stated  here. 

Tyrosine,  C6H4.OH.C2H3(NH2)CO2H  (Para-oxyphenyl-amino-pro- 
pionic  acid).  This  is  obtained  from  all  proteins,  except  collagen  and 
reticulin,  by  trypsin  digestion,  by  prolonged  boiling  with  dilute  acids 
or  alkalies,  by  fusion  with  alkaline  hydroxides,  and  by  putrefaction. 
Tyrosine  is  generally  found  with  leucine ;  both  these  substances  have 
nearly  the  same  physiological  properties  and  pathological  significance. 
They  occur  in  the  intestine  during  the  digestion  of  proteins,  and,  patho- 
logically, they  are  found  in  atheromatous  cysts,  in  pus,  in  abscess  and 
gangrene  of  the  lung,  in  the  urine  during  yellow  atrophy  of  the  liver, 
and  in  phosphorus  poisoning. 

Tyrosine  crystallizes  in  colorless,  fine,  silky  needles,  often  tufted 
(Fig.  81).  It  is  very  slightly  soluble  in  water,  more  so  in  the  pres- 
ence of  alkalies  and  mineral  acids,  insoluble  in  alcohol  and  ether. 
(For  a  method  of  preparing  tyrosine  and  leucine  from  proteins,  see 
Pancreatic  Digestion.) 


PROTEINS.  635 

Analytical  reactions  of  tyrosine. 

1.  Place  a  few  crystals  of  tyrosine  on  a  slide,  and  warm  gently ; 
they  do  not  melt.     (Crystals  of  fatty  acids  found  in  pus  resemble 
tyrosine  in  general  appearance,  but  melt  when  heated,  and  are  insolu- 
ble in  hydrochloric  acid.) 

2.  To  a  very  small  quantity  of  tyrosine  add  water  and  a  few  drops 
of  Millon's  reagent.     On  boiling,  the  mixture  turns  rose  red  ;  and 
on  standing  a  deeper  red  color  develops.     (All  phenols  and  their 
derivatives  show  this  reaction.) 

3.  Peria's  reaction.     Place  a  small  quantity  of  tyrosine  upon  a 
watch-glass,  add  a  few  drops  of  concentrated  sulphuric  acid,  and 
heat  for  half  an  hour  over  a  boiling  water-bath.     Allow  it  to  cool  and 
pour  into  15  c.c.  of  water  contained  in  a  porcelain  evaporating  dish. 
Warm,  neutralize  with  powdered  barium  carbonate,  filter  while  hot, 
evaporate   the  filtrate  to  a  few  cubic  centimeters,  and  add  a  very 
dilute  ferric  chloride  solution  :  a  violet  color  appears. 

Leucine,  C5H10.NH2.CO2H  (Amino-caproie  acid).  This  is  a  con- 
stant product  of  the  cleavage  of  proteins.  It  is  easily  soluble  in 
hot  water,  less  so  in  cold  water,  soluble  in  alcohol,  insoluble  in  ether. 
It  is  easily  soluble  in  acids  and  alkalies,  forming  crystalline  com- 
pounds with  mineral  acids.  When  impure,  leucine  crystallizes  in 
rounded  lumps  which  often  show  radiating  striations  (Fig.  80). 
AVhen  pure  it  forms  white,  glittering,  flat  crystals. 

Analytical  reactions  of  leucine. 

1.  Heat  slowly  in  a  dry  test-tube  a  very  small  portion  of  leucine ; 
it  sublimes  in  the  form  of  woolly  flakes.    If  heated  above  its  melting- 
point,   170°  C.  (338°  F.),   it   decomposes  into  carbon   dioxide   and 
amylamine,  the  latter  substance  having  a  characteristic  odor.     The 

reaction  is  this  : 

C6H13N02    =    C02    +    CBHuNHa. 

2.  Heat  a  little  leucine  in  a  dry  test-tube,  add  a  piece  of  caustic 
soda  and  a  few  drops  of  water.     Heat  until  the  caustic  soda  melts, 
when  ammonia  is  given  off.    Allow  to  cool,  dissolve  in  a  little  water, 
and  acidulate  with  dilute  sulphuric  acid  :  the  odor  of  valeric  acid  is 
noticeable.     (Leucine,  by  this  treatment,  takes  up   oxygen  and  de- 
composes into  valeric  acid,  ammonia,  and  carbon  dioxide.) 

3.  Dissolve  a  little  leucine  in  water,  decolorize  if  necessary  with 
animal  charcoal,  filter,  render  alkaline  with  caustic  soda,  and  add 
2  drops  of  cupric  sulphate  solution.     The  cupric  hydroxide  which  is 


636  PHYSIOLOGICAL  CHEMISTRY. 

precipitated  at  first  dissolves  on  shaking,  giving  a  blue  solution  which 
is  not  reduced  on  heating. 

4.  Sherer's  reaction  (applicable  only  to  very  pure  leucine).  Evapo- 
rate carefully  to  dryness  on  a  platinum  foil  a  small  portion  of  leucine 
with  a  few  drops  of  nitric  acid.  The  residue  is  almost  transparent, 
and  turns  yellow  or  brown  on  the  addition  of  caustic  alkali.  If  this 
mixture  be  again  carefully  concentrated,  an  oil-like  drop  is  obtained, 
which  runs  over  the  foil  in  a  spheroidal  state. 

Hydrolysis. 

In  the  animal  body  a  certain  kind  of  decomposition,  called  hydro- 
lysis or  hydrolytic  cleavage,  is  particularly  prominent.  By  cleavage 
is  meant  the  breaking  up  of  a  complex  molecule  into  simpler  ones,  for 
example,  the  splitting  up  of  dextrose  into  alcohol  and  carbon  dioxide  : 

C6H12O6    ==    2C2H5OH     +     2CO2, 

When  the  splitting  is  accompanied  by  the  decomposition  of  water 
and  the  taking  up  of  its  constituents  by  the  decomposition-products, 
it  is  known  as  hydrolytic  cleavage  or  hydrolysis.  The  special  kind 
of  hydrolysis  is  sometimes  indicated  by  adding  the  suffix  "  lysis  "  to 
a  root  designating  the  nature  of  the  substance  decomposed,  as  pro- 
teolysis  for  hydrolytic  cleavage  of  proteins.  A  familiar  example  of 
this  kind  of  cleavage  is  the  inversion  of  cane-sugar  by  boiling  with 
acidified  water : 

C12H22On     +    H20    :  :    C6H1206    +     C6H1206, 

Hydrolytic  cleavage,  as  has  been  shown,  can  be  brought  about  out- 
side the  body — by  heat,  with  or  without  the  aid  of  acids  or  alkalies, 
and  by  the  action  of  certain  substances  called  enzymes. 

Enzymes  (ferments). 

Enzymes,  as  mentioned  in  Chapter  41,  are  substances  that  decom- 
pose others  without  themselves  undergoing  permanent  change,  i.  e., 
they  are  catalysts.  The  activity  of  all  enzymes  is  impeded  by  accu- 
mulation of  the  products  of  the  fermentation.  The  activity  of  enzymes 
is  controlled  by  the  temperature  and  character  of  the  solution  in 
which  they  act.  There  is  a  certain  temperature  at  which  every 
enzyme  is  most  active — the  "optimum"  temperature.  A  higher 
temperature  first  impairs,  and  then  destroys  its  activity.  All  enzymes 
are  destroyed  by  heating  to  100°  C.  (212°  F.)  with  water.  Cooling 
impairs  their  activity ;  but  even  after  freezing  they  regain  their 
power  when  carefully  brought  to  the  proper  temperature.  Some  act 


PROTEINS.  637 

best  in  neutral,  others  in  either  acid  or  alkaline,  solution  of  certain 
concentration.  The  action  of  enzymes  is  in  many  cases  reversible. 
Thus,  ethyl  butyrate  is  split  by  lipase  into  ethyl  alcohol  and  butyric 
acid ;  and  under  certain  conditions  lipase  will  produce  the  opposite 
effect  and  cause  the  combination  of  alcohol  and  butyric  acid  with  the 
formation  of  ethyl  butyrate. 

As  it  has  been  shown  that  living  "  organized  ferments  "  owe  their 
activity  to  the  enzymes  which  they  secrete,  there  is  less  stress  laid 
now  upon  the  distinction  between  organized  and  unorganized  fer- 
ments, and  the  term  ferment  is  reserved  mainly  for  yeast. 

The  chemical  composition  of  the  enzymes  is  not  known.  As  yet, 
no  enzyme  has  been  prepared  in  the  pure  state ;  they  may  be  extracted 
from  the  cells  by  means  of  water  and  glycerin.  The  solution  in 
glycerin  is  very  stable.  When  in  solution  they  are  easily  obtained 
by  precipitation  of  some  other  substance  from  the  same  solution,  the 
enzyme  being  carried  down  with  the  precipitate.  The  activity  of 
their  solution  is  generally  destroyed  by  heating  to  80°  C.  (176°  F.). 

The  quantitative  estimation  of  enzymes  is  based  on  the  amount  of 
decomposition-products  formed,  or  the  amount  of  material  decom- 
posed in  a  given  time  and  under  certain  conditions. 

Enzymes  occur  widely  distributed  in  animal  and  vegetable  organ- 
isms, and  possess  great  diversity  of  function.  At  present,  enzymes 
are  classified  according  to  the  nature  of  the  changes  they  produce ; 
the  more  prominent  groups  are  : 

Amylases  or  amylolytic  enzymes,  converting  starches  into  simple 
sugars  :  ptyalin,  amylopsin,  malt,  diastase. 

Proteases  or  proteolytic  enzymes,  converting  proteins  into  peptone  or 
simpler  compounds  :  pepsin,  trypsin. 

Steatases  or  steatolytic  enzymes,  splitting  fats  :  steapsin. 

Invertases  or  inverting  enzymes,  splitting  sugar  :  invertin. 

Coagulases  or  coagulating  enzymes,  converting  soluble  proteins  into 
insoluble  forms  :  rennin. 

Oxidases  or  oxidizing*  enzymes.  Oxidases  produce  oxidation  in 
the  presence  of  oxygen,  peroxidases  (catalases),  only  in  the  presence 
of  a  peroxide.  Oxygenases  are  theoretical  enzymes,  capable  of  first 
combining  with  oxygen  and  then  transferring  it  to  some  other  sub- 
stance. 

Of  glucoside-splitting  enzymes  has  been  mentioned,  in  Chapter  50, 
emulsin  or  synaptase,  which  decomposes  amygdalin,  while  myrosin 
acts  on  sinigrin  found  in  mustard  seed. 

Not  infrequently  the  enzymes  of  the  body  are  secreted  in  an  inac- 


638  PHYSIOLOGICAL   CHEMISTRY. 

tive  state,  and  are  then  spoken  of  as  zymogens  or  pro-enzymes.  These 
zymogens  become  active  in  the  presence  of  certain  supplementary 
substances.  These  substances  are  called  kinases  if  of  organic  nature, 
and  activators  if  of  inorganic  nature.  Thus,  enterokinase  is  the  kinase 
of  trypsinogen,  converting  it  into  trypsin,  while  hydrochloric  acid  is 
the  activator  of  pepsinogen,  converting  it  into  pepsin. 

While  enzymes  will  be  fully  considered  later,  the  following  two 
are  mentioned  here  because  they  furnish  official  preparations. 

Pepsin  is  one  of  the  active  principles  of  gastric  juice,  capable  of 
converting  albumin,  in  the  presence  of  hydrochloric  acid,  into  soluble 
peptones.  While  pure  pepsin  is  not  known,  a  number  of  preparations 
containing  more  or  less  of  this  ferment  are  sold  as  pepsin.  They  are 
obtained  by  dhTerent  processes  of  extraction  from  the  glandular  layer 
of  fresh  stomachs  from  healthy  pigs. 

Pepsin,  U.  S.  P.,  should  be  either  a  fine,  white,  or  yellowish-white, 
amorphous  powder,  or  consist  of  thin,  pale  yellow  or  yellowish, 
transparent  or  translucent  grains  or  scales.  It  should  be  capable 
of  digesting  not  less  than  3000  times  its  own  weight  of  freshly 
coagulated  and  disintegrated  egg  albumin. 

Experiment  72.  Use  the  U.  S.  P.  process  for  the  valuation  of  pepsin,  as  fol- 
lows :  "  Mix  9  c.c.  of  diluted  hydrochloric  acid  with  291  c.c.  of  distilled  water, 
and  dissolve  the  pepsin  in  150  c.c.  of  the  acid  liquid.  Immerse  a  hen's  egg, 
which  should  be  fresh,  during  fifteen  minutes  in  boiling  water ;  remove  the 
pellicle  and  all  of  the  yolk  ;  rub  the  white,  coagulated  albumin  through  a  clean 
No.  40  sieve.  Reject  the  first  portion  that  passes  through  the  sieve,  and  place 
10  Gin.  of  the  succeeding  portion  in  a  wide-mouthed  bottle  of  100  c.c.  capacity. 
Add  20  c.c.  of  the  acid  liquid,  and  with  the  aid  of  a  glass  rod  tipped  with  cork 
or  black  rubber  tubing,  completely  disintegrate  the  albumin ;  then  rinse  the  rod 
with  15  c.c.  more  of  the  acid  liquid  and  add  5  c.c.  of  the  solution  of  pepsin. 
Cork  the  bottle  securely,  invert  it  three  times,  and  place  it  in  a  water-bath  that 
has  previously  been  regulated  to  maintain  a  temperature  of  52°  C.  (125.6°  F.). 
Keep  it  at  this  temperature  for  two  and  one-half  hours,  agitating  every  ten 
minutes  by  inverting  the  bottle  once.  Then  remove  it  from  the  water-bath, 
add  50  c.c.  of  cold  distilled  water,  transfer  the  mixture  to  a  100  c.c.  graduated 
cylinder,  and  allow  it  to  stand  for  half  an  hour.  The  deposit  of  undissolved 
albumin  should  not  then  measure  more  than  1  c.c. 

"The  relative  proteolytic  power  of  pepsin  stronger  or  weaker  than  that  just 
described  may  be  determined  by  ascertaining  through  repeated  trials  the 
quantity  of  the  above  pepsin  solution  required  to  digest,  under  the  prescribed 
conditions,  10  grammes  of  boiled  and  disintegrated  egg  albumin.  Divide  15,000 
by  this  quantity  expressed  in  c.c.  to  ascertain  how  many  parts  of  egg  albumin 
one  part  of  the  pepsin  will  digest." 

Pancreatin,  U.  S.  P.  This  preparation  is  a  mixture  of  the 
enzymes  existing  in  the  pancreas  of  warm-blooded  animals,  and  is 


CHEMICAL   CHANGES  IN  PLANTS  AND  ANIMALS.          639 

usually  obtained  from  the  fresh  pancreas  of  the  hog.  It  consists 
principally  of  amylopsin,  myopsin,  trypsin,  and  steapsin.  It  is  a 
yellowish  or  grayish,  almost  odorless  powder,  soluble  in  water  to  the 
extent  of  90  per  cent.,  insoluble  in  alcohol.  It  has  the  power  to 
digest  proteins,  and  should  convert  not  less  than  twenty-five  times  its 
own  weight  of  starch  into  sugar. 

Experiment  73.  Introduce  7.5  grammes  of  starch  into  a  flask,  add  120  c.c. 
of  distilled  water,  and  boil  until  a  translucent  mixture  results.  Cool  the 
resulting  paste  to  40.5°  C.  (105°  F.),  and  add  to  it  0.3  gramme  of  pancreatin, 
previously  dissolved  in  about  10  c.c.  of  distilled  water  at  40.5°  C.  (105°  F.). 
Shake  the  flask  well,  maintaining  the  temperature  of  the  mixture  at  40.5°  C. 
(105°  F.)  during  five  minutes ;  at  the  end  of  this  time  all  of  the  starch  should 
be  converted  into  substances  soluble  in  water,  and  a  thin  liquid  be  produced. 
Mix  2  drops  of  tenth-normal  iodine  V.  S.  with  60  c.c.  of  distilled  water,  and 
add  to  it  2  drops  of  the  warm  converted  starch  solution  ;  no  color  should  result, 
or,  at  most,  a  wine-red  color,  showing  the  presence  of  dextrin  and  maltose. 
The  appearance  of  a  blue  or  purple  color  indicates  the  presence  of  unconverted 
starch  and  that  the  pancreatin  is  below  the  standard— i.  e.,  that  of  converting 
not  less  than  25  times  its  own  weight  of  starch  into  substances  soluble  in  water. 


54.   CHEMICAL  CHANGES  IN  PLANTS  AND  ANIMALS. 

Difference  between  vegetable  and  animal  life.  As  a  general 
rule,  it  may  be  stated  that  the  chemical  changes  in  a  plant  are  pro- 
gressive or  constructive,  in  an  animal  regressive  or  destructive.  That  is 
to  say,  plants  take  up  as  food  a  small  number  of  inorganic  substances 
of  a  comparatively  simple  composition,  convert  them  into  organic 
substances  of  a  more  and  more  complicated  composition  with  the 
simultaneous  liberation  of  oxygen,  while  animals  take  up  as  food 
these  organic  vegetable  substances  of  a  complex  composition,  assim- 
ilating them  in  their  system,  where  they  are  gradually  used  (burned 
up)  and  finally  discharged  as  waste  products,  which  are  identical  (or 
nearly  so)  with  those  substances  serving  as  plant  food. 

QUESTIONS. — To  which  class  of  substances  is  the  term  protein  applied,  and 
which  elements  enter  into  their  composition?  How  are  proteins  classified,  and 
how  do  these  groups  differ  from  each  other?  Describe  the  five  color-reactions 
of  proteins.  Mention  the  conditions  necessary  for  the  coagulation  of  a  protein 
solution  by  heat ;  and  state  how  coagulation  differs  from  precipitation.  De- 
scribe the  products  of  proteolysis.  Describe  the  nucleoproteins.  Give  a  full 
description  of  the  nature  and  action  of  enzymes.  State  the  composition  and 
properties  of  tyrosine  and  leucine.  Define  hydrolytic  cleavage.  Mention  two 
enzymes  that  are  official;  state  their  sources  and  their  function  in  the  process 
of  digestion. 


640  PHYSIOLOGICAL   CHEMISTRY. 

Plant  food.  Waste  products  of  animal  life. 

Carbon  dioxide.  Carbon  dioxide. 

Water.  Water. 

Ammonia,  NH3.  Urea,     CO(NH2)2. 

Nitrates,     MzNO3.  Urates,  MzCsH2N4O3. 

f  Calcium.  f  Calcium. 

Phosphates  ,            |  M         ium_  Phosphates  |           ,  M         ium. 

Sulphates      -    of        Sodi(]m  Su  phates      .    of        godium 

Chlorides     )               potassium^  Chlondes     J               Pw^ium. 


It  should  be  remembered  that  no  sharply  defined  line  of  demarca- 
tion can  be  drawn  between  plants  and  animals.  Synthetic  processes 
occur  in  the  body  of  animals,  and  cleavage  processes  take  place  in 
some  plants.  However,  in  the  animal  organism  the  processes  of  oxi- 
dation and  cleavage  are  predominant,  while  in  plants  those  of  deoxi- 
dation  and  synthesis  are  prevalent. 

Formation  of  organic  substances  by  the  plant.  As  shown  in 
the  preceding  table,  plants  take  up  the  necessary  elements  for  organic 
matter  from  a  comparatively  small  number  of  compounds.  All  carbon 
is  derived  from  carbon  dioxide ;  hydrogen  chiefly  from  water ;  oxygen 
from  either  of  the  two  substances  named,  as  well  as  from  the  various 
salts ;  nitrogen  either  from  ammonia,  or  from  nitrates  or  nitrites ; 
while  sulphur  and  phosphorus  are  derived  from  sulphates  and  phos- 
phates respectively.  These  substances  are  taken  into  the  plant  chiefly 
by  the  roots,  the  assimilation  of  the  necessary  mineral  constituents 
being  facilitated  by  an  acid  secretion  (discharged  from  the  roots) 
which  has  a  tendency  to  render  these  salts,  present  in  the  soil  and 
surrounding  the  roots,  soluble. 

Water  having  absorbed  more  or  less  of  carbon  dioxide,  of  ammonia 
or  ammonium  salts,  and  of  nitrates,  phosphates,  and  sulphates  of 
potassium,  calcium,  etc.,  enters  the  plant  through  the  roots  by  a  simple 
process  of  diffusion,  and  is  carried  to  the  various  green  parts  of  the 
plant  (chiefly  to  the  leaves),  where,  under  the  influence  of  sunlight,  a 
chemical  decomposition  and  the  formation  of  new  compounds  take 
place,  the  liberated  oxygen  being  discharged  directly  through  the 
leaves  into  the  atmosphere. 

It  is  difficult  to  explain  fully  the  process  of  the  formation  of  highly  complex 
organic  compounds  in  the  plant,  because  we  know  so  little  in  regard  to  the 
intermediate  products  which  are  formed.  However,  it  is  fair  to  assume  that 
the  various  compounds  above  mentioned  as  plant  food  are  first  decomposed 
(with  liberation  of  oxygen)  in  such,  a  manner  that  residues  or  unsaturated 
radicals  are  formed,  which  combine  together.  From  these  compounds,  pro- 


CHEMICAL   CHANGES  IN  PLANTS  AND  ANIMALS.          641 

duced  at  first,  more  complicated  ones  will  be  formed  gradually  by  replacement 
of  more  hydrogen,  oxygen,  or  other  atoms  by  other  residues. 

The  following  equations,  while  not  showing  the  various  radicals  and  inter- 
mediate compounds  formed,  may  illustrate  some  of  the  results  obtained  by  the 
plant  in  forming  organic  compounds : 

C02  +     H20  ==  H2CO3 

H2CO3  —  O  =  H2C02  =  Formic  acid. 
2C02  +     H20  =  H2C205 

H2C2O5  —  O  =  H2C.,O4  =  Oxalic  acid. 
6C02  +  6H20  =  C6H12018 

C6H12O18  —  12O  =  C6H12O6  =  Glucose. 
10C02  +  8H20  =  C10H16028 

Ci0H16O,8  —  28O  =  C10H16  =  Oil  of  turpentine. 
10C02  +  4H20  +  2NH3  =*  C,0H14O24N2 

C10HU024N2  —  24O  =  C10HUN2  =  Nicotine. 

The  above  formulas  show  that  the  formation  of  organic  compounds  in  the 
plant  is  always  accompanied  by  the  liberation  of  oxygen,  and  it  may  be  stated, 
as  a  general  rule,  that  no  organic  substance  (produced  in  nature)  contains  a 
quantity  of  oxygen  sufficient  to  convert  all  carbon  into  carbon  dioxide  and  all 
hydrogen  into  water,  which  fact  also  explains  the  combustibility  of  all  organic 
substances. 

Why  it  is  that  the  living  plant  has  the  power  of  forming  organic  substances 
in  the  manner  above  indicated,  we  know  not,  and  we  know  very  little  even  in 
regard  to  the  means  by  which  the  living  cell  accomplishes  this  formation,  fcut 
we  do  know  that  sunlight  furnishes  the  kinetic  energy  necessary  in  the  forma- 
tion of  complex  substances  from  the  simpler  ones.  This  kinetic  energy  is 
transformed  into  the  potential  energy,  or  chemical  tension,  of  the  new  com- 
pounds and  of  the  liberated  oxygen. 

Animal  food.  Those  substances  which  when  taken  into  the  body 
yield  energy,  build  tissue,  or  prevent  the  consumption  of  tissue, 
without  injury  to  the  organism,  are  called  animal  foods.  The  food 
taken  by  animals  is  (beside  water  and  a  few  of  its  mineral  con- 
stituents) all  derived  from  vegetables,  but  it  is  taken  from  them 
either  directly  or  indirectly ;  in  the  latter  case  it  has  been  taken  pre- 
viously into  and  assimilated  by  other  animals,  as  in  case  of  food 
taken  in  the  form  of  meat,  milk,  eggs,  etc.  While  some  animals 
(herbivora)  feed  upon  vegetable,  and  some  (carnivora)  upon  animal 
food  exclusively,  others  are  capable  of  taking  and  assimilating  either. 

The  fact  that  animal  food  is  derived  from  vegetable  matter  renders 
it  superfluous  to  state  that  the  elements  taking  an  active  part  in  the 
formation  of  either  vegetable  or  animal  matter  are  identical.  Of  the 
total  number  of  the  elements,  only  15  are  found  as  necessary  con- 
stituents of  the  animal  body.  These  elements  are  carbon,  hydro- 
gen, oxygen,  nitrogen,  sulphur,  phosphorus,  chlorine,  iodine,  fluorine, 
silicon,  calcium,  magnesium,  sodium,  potassium,  and  iron.  A  few 

41 


642  PHYSIOLOGICAL   CHEMISTRY. 

other  elements,  such  as  aluminum,  manganese,  copper,  etc.,  are  some- 
times found  in  the  animal  system,  but  they  cannot  be  looked  upon 
as  normal  or  necessary  constituents. 

,  The  various  kinds  of  animal  food  are  derived  chiefly  from  three 
groups  of  organic  substances,  viz.,  carbohydrates  (sugars,  starch,  etc.), 
fats,  and  proteins  or  nitrogenous  substances.  The  inorganic  sub- 
stances, such  as  phosphates,  chlorides,  etc.,  required  by  the  animal  in 
the  construction  of  bones,  for  the  liberation  of  hydrochloric  acid  in 
the  gastric  juice,  etc.,  are  generally  found  as  constituents  of  various 
kinds  of  food  or  are  derived  from  drinking  water.  Milk  contains  all 
the  necessary  organic  or  inorganic  constituents ;  bread  is  rich  in  phos- 
phates, which  latter  are  also  found  in  smaller  or  larger  quantities  in 
nearly  all  kinds  of  vegetable  and  animal  food. 

Through  the  food  are  supplied  those  compounds  which  supply  the 
constituents  that  replace  the  exhausted  material  of  the  living  cells, 
and  by  chemical  changes  their  inherent  potential  energy  is  converted 
into  the  heat  of  the  body  and  into  the  kinetic  energy  used  in  work- 
ing the  living  mechanism.  While  the  nitrogenous  substances  have 
primarily  the  task  of  continuously  replacing  the  wear  and  tear  of  the 
nitrogenous  tissues,  they  also  serve,  together  with  non-nitrogenous 
food,  to  yield  the  animal  heat,  as  also  muscular  and  other  power  for 
the  work  which  the  body  performs.  To  a  certain  extent  the  different 
nutrients  can  do  the  work  of  one  another.  Thus,  the  body  can  burn 
protein  in  place  of  fats  or  carbohydrates,  but  neither  of  the  latter  can 
replace  the  protein  in  building  or  repairing  tissue.  On  the  other 
hand,  the  fats  and  carbohydrates,  while  being  consumed,  protect  the 
proteins. 

To  some  extent,  the  animal  body  may  be  regarded  as  a  complicated  machine, 
in  which  the  potential  energy,  supplied  by  the  food,  is  converted  into  actual 
energy  of  heat  and  mechanical  labor.  The  main  difference  is  that  in  our 
machines  the  fuel  serves  as  the  source  of  energy  only,  while  in  the  body  the 
food  is  mainly  changed  first  into  tissue  (thus  building  up  and  renewing  the 
body  constantly),  serving  as  fuel  afterward.  While  in  the  best  steam-engine 
only  one-tenth  of  the  fuel  is  utilized  as  mechanical  work,  one-fifth  of  the  energy 
of  the  food  is  realized  in  the  human  body. 

Heat  and  muscular  power  are  forms  of  energy  developed  by  the 
consumption  of  food  in  the  body.  The  amount  of  energy  developed 
is  the  measure  of  the  food  value  of  any  nutrient,  and  the  unit  of 
value  is  the  calorie. 

While  each  individual  substance  generates  a  definite  number  of 
calories  during  combustion,  for  practical  purposes  it  is  sufficiently 
accurate  to  estimate  the  average  amount  of  heat  and  energy  in  1 


CHEMICAL   CHANGES  IN  PLANTS  AND  ANIMALS. 


643 


pound  of  either  proteins  or  carbohydrates  as  1860  calories,  while 
that  in  a  pound  of  fat  is  equal  to  4220  calories. 

It  is  important  to  notice  that  carbohydrates  and  fats  are  oxidized 
to  carbon  dioxide  and  water,  thus  producing  the  theoretical  yield  of 
energy  in  the  body,  while  only  part  of  the  protein  molecule  is  reduced 
to  carbon  dioxide  and  water,  the  remainder  appearing  as  urea  and 
other  nitrogenous  bodies  possessing  latent  energy,  which  must  be  sub- 
tracted from  the  theoretical  heat  value  of  the  protein. 

Composition  and  fuel  values  of  several  important  food  materials  are 
given  in  the  following  table: 


• 

Water. 

Proteins. 

Fats. 

Carbohy- 
drates. 

Mineral 
matter. 

Value  of  1 
pound  in 
calories. 

Bread  .                           . 
Wheat  flour 
Oatmeal 
Kice     .                           . 
White  beans 
Dried  peas  . 
Potatoes 
Sweet  potatoes 
Turnips 
Milk    

32.0 
12.5 

7.6 
12.4 
12.6 
12.3 

78.9 
71.1 
89.4 
87  0 

9.0 
11.0 
15.1 
7.4 
23.1 
26.7 
2.1 
1.5 
1.2 
36 

2.0 
1.1 
7.1 
0.4 
2.0 
1.7 
0.1 
0.4 
0.2 
40 

56.0 
74.9 
68.2 
79.4 
59.2 
56.4 
17.9 
26.0 
8.2 
47 

1.0 
0.5 
2.0 
0.4 
3.1 
2.9 
1.0 
1.0 
1.0 
07 

1300 
1645 
1850 
1630 
1615 
1565 
375 
530 
185 
325 

Butter  
Cheese,  full  cream 
Cheese,  skimmed  milk 
Egg     

10.5 
30.2 
41.3 
738 

1.0 

28.3 
38.4 
149 

85.0 
35.5 
68 
10.5 

0.5 

1.8 
8.9 

3.0 
4.2 

4.6 
08 

3615 
2070 
1165 
721 

Beef,  sirloin 
Mutton,  shoulder 
Veal,  shoulder     . 
Pork,  fresh  .... 

60.0 
58.6 
68.8 
50.3 

18.5 
18.1 
20.2 
16.0 

20.5 
22.4 
9-8 
32.8 

• 

1.0 
0.9 
1.2 

0.9 

1210 
1260 
790 
1680 

The  relative  proportions  in  which  the  two  kinds  of  food  are  taken 
by  animals  depend  upon  the  nature  of  the  animal  and  upon  its  par- 
ticular condition  of  existence. 

Below  are  given  in  column  A  the  daily  quantity  of  food  required 
to  maintain  a  grown  person  in  good  health,  with  neither  loss  nor 
gain  in  weight,  while  the  figures  in  column  B  refer  to  the  quantities 
of  food  for  a  working  man  of  average  height  and  weight. 


Proteins 125  grammes. 

Fats 79 

Carbohydrates          .         .         .         .485         " 
Inorganic  salts         .         .         .         .25         " 

Water 2600 

Equivalent  to 3050  calories. 

The  above  nutrients  will  be  furnished  by  a  diet  consisting  of  1.5 


B. 

130  grammes. 
85         " 
400 

30  " 
2600  " 
3800  calories. 


644  PHYSIOLOGICAL   CHEMISTRY. 

to  2  pounds  of  bread,  10  to  14  ounces  of  lean  beef,  2  to  3  ounces  of 
butter,  with  2  quarts  of  water. 

Digestibility.  In  providing  a  diet,  it  must  be  borne  in  mind  that 
the  digestibility  of  a  food  is  more  a  measure  of  its  nutritive  value  than 
its  elementary  composition.  Different  foods  show  great  differences 
in  the  rapidity  and  completeness  with  which  they  are  absorbed. 
Thus  eggs,  fresh  meat,  white  bread,  and  butter  are  absorbed  and 
assimilated  more  readily  than  pork,  rye  bread,  potatoes,  green  vege- 
tables, and  bacon. 

By  digestibility  of  food  many  different  conditions  are,  or  may  be,  implied. 
Some  of  these,  as  the  ease  with  which  a  certain  food  is  digested,  the  time  re- 
quired for  the  process,  the  influence  of  different  substances  and  conditions  on 
digestion,  and  the  effects  on  health  and  comfort,  are  so  dependent  upon  indi- 
vidual peculiarities,  that  no  definite  rule  for  the  measurement  of  food-digesti- 
bility can  be  established.  Fortunately,  the  most  important  factor,  viz.,  the 
amount  digested,  can  be  determined  accurately  by  experiment.  The  method 
consists  in  analyzing  and  weighing  both  the  food  consumed  and  the  feces 
excreted,  the  difference  being  taken  as  the  amount  digested. 

In  general  it  can  be  said  that  animal  protein  is  easily  and  completely  di- 
gested, while  protein  of  vegetable  food  is  less  so.  Thus,  of  the  protein  contained 
in  potatoes,  whole  wheat,  and  rye  flour,  one-fourth,  or  more,  may  escape  diges- 
tion, and  thus  be  rendered  useless  as  nourishment.  About  5  per  cent,  of  fats 
escape  digestion,  while  carbohydrates  are,  in  general,  completely  digested, 
cellulose  being  the  only  exception. 

In  adjusting  a  diet,  it  is  important  to  provide  sufficient  protein  for  the  build- 
ing and  repair  of  tissue,  and  enough  of  other  materials  to  furnish  the  body 
with  heat  and  energy  for  the  work  to  be  performed.  A  proper  diet  for  a  grown 
person  doing  moderate  work  should  provide  about  3500  calories  of  energy  with 
a  nutritive  ratio  of  from  1 :  4  to  1 :  6. 

The  nutritive  ratio  is  the  ratio  of  the  protein  to  the  sum  of  all  the  other 
nutritive  ingredients.  The  fuel  value  of  fats  is  two  and  a  quarter  times  that 
of  proteins  and  carbohydrates,  that  of  the  two  latter  being  considered  to  be 
alike.  In  calculating  the  nutritive  ratio,  the  quantity  of  fats  is  multiplied  by 
2.25,  and  the  product  added  to  the  weight  of  carbohydrates.  The  sum  divided 
by  the  weight  of  protein  gives  the  nutritive  ratio. 

If  less  protein  be  administered  than  is  needed  for  repair,  although  a  sufficient 
number  of  calories  be  provided,  more  nitrogen  will  be  excreted  in  the  urine 
than  is  contained  in  the  food.  When  the  protein  is  given  in  sufficient  quantity 
to  replace  the  worn  tissues,  sufficient  calories  being  also  provided  for,  a  nitroge- 
nous equilibrium  is  established — i.  e.,  the  nitrogen  excreted  equals  the  nitrogen 
administered.  Should  more  protein  than  is  necessary  be  administered,  with 
sufficient  calories,  then  more  nitrogen  is  excreted  and  thereby  the  equilibrium, 
as  far  as  nitrogen  is  concerned,  is  rapidly  re-established. 

During  the  periods  of  growth  and  convalescence  from  acute  disease  the  pro- 
teins can  be  increased  in  the  body  by  increase  of  protein  food.  The  nitrogenous 
equilibrium  is  then  less  rapidly  re-established,  as  nitrogenous  matter  is  utilized 


CHEMICAL   CHANGES  IN  PLANTS  AND  ANIMALS.          645 

in  the  construction  of  new  tissue.  When  the  quantity  of  food  absorbed  is 
greater  than  is  required  for  repair  and  energy,  the  carbohydrates  are  converted 
into  fat,  and  this,  with  the  excess  of  fat  from  the  food,  is  stored  up  in  the 
fatty  tissue  of  the  body,  to  be  drawn  upon  whenever  needed.  In  starvation  no 
tissue  decreases  as  much  as  the  fatty.  The  fatty  tissue  of  the  animal  body  is  a 
depot  where,  during  proper  alimentation,  nutritive  material  of  great  value  is 
stored,  to  be  given  off  as  it  may  be  needed. 

Nutrition.  In  the  process  of  nutrition  five  phases  may  be  distin- 
guished, viz. :  Digestion,  absorption,  anabolism,  catabolism,  and  excre- 
tion of  waste  products.  These  processes  are  commonly  spoken  of 
collectively  as  metabolism. 

Digestion  is  the  process  of  converting  food  material  into  dialyzable 
compounds,  or  into  other  forms  of  matter  capable  of  absorption.  Ab- 
sorption is  the  mechanical  process  of  transferring  the  digested  mate- 
rials from  the  alimentary  canal  into  the  circulation.  Anabolism 
includes  the  synthetic  changes  taking  place  after  they  are  absorbed 
until  they  have  become  a  part  of  living  cells.  Catabolism  includes 
those  destructive  changes  which  take  place  chiefly  in  consequence  of 
oxidation,  the  oxygen  being  supplied  during  the  process  of  respira- 
tion. Excretion  of  waste  products  is  the  discharge  of  that  material 
which  is  no  longer  needed  in  the  system. 

Digestion.  It  has  been  stated  before  that  foods  are  divided  into 
two  classes,  inorganic  and  organic,  and  that  the  latter  are  subdivided 
into  proteins,  carbohydrates,  and  fats.  As  a  rule,  the  inorganic  foods 
are  taken  into  the  body  without  chemical  change.  Before  the  organic 
foods  can  be  absorbed  they  have  to  undergo  digestion.  This  is  the 
process  by  which  organic  compounds  capable  of  acting  as  foods  are  so 
altered  that  they  may  be  absorbed.  The  process  of  digestion  will  be 
fully  considered  in  a  later  chapter. 

Absorption,  anabolism,  catabolism,  excretion.  While  these  subjects, 
particularly  absorption  and  excretion,  are  considered  later  under  the 
various  organs  concerned  (see  Index),  a  brief  statement  of  the  changes 
in  the  various  food-stuffs,  subsequent  to  their  absorption,  is  made 
here. 

Carbohydrates.  The  carbohydrates,  mainly  as  dextrose,  are  carried 
from  the  intestine  by  the  portal  system  to  the  liver,  where  the  bulk 
of  them  is  dehydrated  and  converted  into  glycogen.  Some  of  the 
dextrose  is  changed  into  glycogen  by  the  muscle,  and  in  this  organ 
and  the  liver  a  reserve-supply  of  glycogen  is  stored  up.  This  gly- 
cogen forms  the  most  readily  available  source  of  energy  for  the  body. 
When  used  it  is  first  split  into  dextrose,  and  then  oxidized  to  carbon 
dioxide  and  water,  passing  probably  through  a  lactic  acid  stage.  The 


646  PHYSIOLOGICAL   CHEMISTRY. 

sugar  metabolism  is  so  carefully  controlled  and  is  influenced  by  so 
many  factors  that  the  details  are  not  clear.  The  question  has  been 
largely  studied  by  observation  of  cases  of  spontaneous  and  experi- 
mental diabetes.  This  term  implies  much  more  than  a  mere  glyco- 
suria ;  hyperglucsemia  (excessive  amount  of  sugar  in  the  blood)  must 
be  present,  and  there  is  a  profound  change  in  the  handling  of  carbo- 
hydrates by  the  body,  as  well  as  some  derangement  of  the  protein  and 
fat  metabolism.  The  pancreas  plays  an  important  role  and  furnishes 
an  internal  secretion  from  the  islands  of  Langerhans,  which  probably 
enables  the  muscle  to  split  and  oxidize  the  glycogen  as  it  needs  it. 
The  muscle  is  thus  involved,  as  well  as  the  liver,  in  sugar  control. 
The  adrenal  is  thought  perhaps  to  control  the  transportation  of  sugar 
in  the  body,  for  example,  its  removal  from  the  liver  to  the  muscle ; 
while  the  thyroid  seems  to  have  an  inhibitory  action  upon  both  the 
pancreas  and  the  adrenal.  Phloridzin  produces  an  increased  perme- 
ability of  the  kidney  to  sugar,  but  not  a  true  diabetes. 

Fats.  Shortly  after  the  emulsified  fats  reach  the  blood  through 
the  thoracic  duct  from  the  intestine,  there  occurs  a  peculiar  change  in 
them  whereby  they  become  dialyzable,  soluble  in  water,  and  insoluble 
in  ether.  The  nature  of  this  change  is  entirely  obscure.  The  fats 
are  deposited  in  the  body  as  fats  and  form  a  reserve  store  of  potential 
energy.  A  small  proportion  is  synthesized  into  the  lecithins.  While 
the  fat  of  any  animal  tends  to  remain  true  to  the  composition  charac- 
teristic of  that  animal,  there  is  so  little  change  in  fat  during  digestion 
that  it  is  possible  to  recognize,  in  the  tissue  of  the  animal,  foreign  fats 
which  have  been  introduced  with  the  food.  The  fat  of  the  body  is 
derived  primarily  from  the  fat  of  the  food,  but  is  also  formed  in  con- 
siderable amount  from  carbohydrates.  The  location  of  this  transfor- 
mation of  carbohydrate  to  fat  is  unknown.  There  is  a  possibility  that 
protein  also  may  form  fat,  as  it  can  undoubtedly  form  sugar,  which 
might  be  further  changed  to  fat.  Experiments  in  feeding  foreign 
fats  have  shown  that  the  so-called  fatty  degenerations  of  the  liver, 
etc.,  are  not  transformations  of  protein  into  fat,  but  that  the  fat  is 
brought  by  the  blood  and  deposited  in  the  diseased  organ.  When  fat 
is  burned  it  is  first  saponified.  The  final  products  are  carbon  dioxide 
and  water.  The  acetone  bodies  of  the  urine  are  believed  to  represent 
steps  in  the  incompleted  oxidation  of  the  fats. 

Proteins.  After  the  proteins  enter  the  portal  blood  as  native  pro- 
teins they  pass  through  the  liver,  probably  with  little  change,  and 
are  distributed  to  the  tissues.  Here  a  part  enters  into  the  repair  or 
the  growth  of  the  protein  tissues  ("  tissue  protein  "),  while  a  part  is 


CHEMICAL   CHANGES  IN  PLANTS  AND  ANIMALS.          647 

immediately  broken  down  without  actually  being  incorporated  by  the 
tissues  ("circulating  protein").  This  is  evidenced  by  the  marked 
increase  in  the  nitrogenous  excretion  which  appears  shortly  after 
protein  ingestion.  It  is  important  to  notice  that  carbohydrate  and 
fat  can  replace  one  another  in  the  diet,  but  that  neither  can  replace 
protein  to  more  than  a  slight  extent.  Indeed,  it  has  very  recently 
been  shown  that  not  all  proteins  have  the  same  nutritive  value  (Os- 
borne  and  Mendel).  Thus,  an  animal  can  thrive  upon  a  single  pro- 
tein, such  as  casein,  egg-albumen,  or  glutenin  (wheat).  It  will  live, 
but  will  not  grow  to  maturity  upon  gliadin  (wheat)  or  hordein  (bar- 
ley) alone.  It  will  not  even  live  upon  zein  (maize).  This  difference 
in  typical  proteins  is  undoubtedly  due  to  differences  in  the  amino- 
body  content  of  the  protein.  Zein  contains  no  lysine  or  tryptophane. 
It  has  long  been  known  that  the  albuminoid  substance,  gelatin,  con- 
taining no  tryptophaue  and  no  tyrosine,  cannot  replace  protein. 

It  is  believed  that  these  deficiencies  in  amino-acids  make  it  im- 
possible for  the  organism  to  build  up  its  native  protein  from  such 
material. 

The  specific  waste  products  of  protein  (meat)  metabolism,  the 
nitrogenous  excreta,  appear  mainly  in  the  urine,  and  will  for  the 
most  part  be  considered  in  that  connection,  while  the  formation  of 
urea  and  certain  other  substances  will  be  discussed  with  the  liver. 

Respiration.  The  most  important  changes  in  respired  air  are  the 
changes  in  the  quantities  of  oxygen  and  carbon  dioxide.  Pure  air, 
after  being  dried,  contains,  by  volume,  of  oxygen  20.8  per  cent.,  of 
nitrogen  79.2  per  cent.,  and  a  quantity  of  carbon  dioxide  (0.04  per 
cent.)  so  small  that  it  need  not  be  considered.  When  100  volumes  of 
air  have  been  breathed  once,  it  gains  a  little  more  than  four  parts  of 
carbon  dioxide  and  loses  a  little  more  than  five  parts  of  oxygen ;  so 
that  the  composition  of  100  volumes  of  inspired  air,  when  expired,  is, 
after  being  dried,  oxygen  15.4  parts,  nitrogen  79.2  parts,  and  carbon 
dioxide  4.3  parts  by  volume. 

Much  the  greater  portion  of  the  oxygen  lost  from  respired  air 
enters  into  combination  with  the  haemoglobin ;  a  small  portion  is 
absorbed  by  the  blood-serum.  The  immediate  source  of  the  carbon 
dioxide  is  the  blood,  in  which  it  exists  partly  in  simple  solution  and 
partly  in  a  loose  combination  with  hemoglobin. 

The  blood  is  the  common  carrier  of  the  body  :  from  the  alimentary 
canal  it  receives  ultimately  all  the  food  material ;  from  the  lungs  it 
receives  oxygen  ;  these  it  carries  to  the  tissues  for  their  sustenance ; 


648  PHYSIOLOGICAL   CHEMISTRY. 

from  the  tissues  it  receives  the  products  of  catabolism,  and  carries 
them  to  their  proper  organs  of  elimination. 

The  bright  red  color  of  the  arterial  blood  is  due  to  oxyhaBmoglobin. 
A  large  portion  of  this  oxygen  absorbed  by  the  haemoglobin  is  given 
up  to  the  tissues  as  the  blood  passes  through  the  capillaries,  and  we 
have  then  the  reduced  hemoglobin,  to  which  is  due  the  dark  color  of 
the  venous  blood. 

In  almost  the  reverse  manner,  the  hemoglobin  takes  up  carbon  from 
the  tissues  and  conveys  it  to  the  lung.  It  is  important  to  note  that 
carbon  dioxide,  in  distinction  from  carbon  monoxide,  is  not  attached  to 
hemoglobin  in  the  same  manner  in  which  the  oxygen  is  attached.  It 
has  been  shown  that  the  dark  color  of  the  venous  blood  is  not  due  to 
the  presence  of  carbon  dioxide,  but  to  a  decrease  of  the  oxygen. 

The  details  of  the  manner  in  which  oxidation  in  the  animal  body  is  induced 
and  how  it  proceeds  are  not  known.  In  some  way  the  atmospheric  oxygen, 
which  under  ordinary  conditions  has  no  action  on  the  proteins,  fats,  and  carbo- 
hydrates, is  so  changed  as  to  become  active.  It  is  commonly  believed  that  the 
process  is  carried  on  by  enzymes,  some  of  which  (peroxidases)  have  been  actually 
demonstrated,  while  others  (oxygenases)  are  merely  hypothetical  (see  page  637). 

Waste  products  of  animal  life.  The  changes  which  the  food 
suffers  after  having  been  absorbed  by  the  animal  system  are  ex- 
tremely complicated,  and  far  from  being  thoroughly  understood. 
Numerous  products  and  organs  are  formed  and  nourished  from  and 
by  the  blood  ;  among  them  muscular,  nerve,  and  brain  substance,  ex- 
cretions and  secretions,1  such  as  milk,  saliva,  bile,  gastric  and  pan- 
creatic juice,  etc.,  together  with  bones,  teeth,  hair,  and  many  others. 

Most  of  these  substances  (some  secretions,  such  as  milk  and  others, 
excepted)  suffer  a  constant  oxidation  in  the  system,  and  are  finally 
eliminated  as  waste  products  ;  in  regard  to  the  intermediate  com- 
pounds formed  in  the  tissues  we  know  little,  but  it  is  highly  probable 
that  the  reduction  of  the  complicated  food  material  to  the  simple 
forms  of  the  waste  products  is  very  gradual.  There  are  three  chan- 
nels through  which  the  waste  products  are  given  off;  they  are  the 
lungs,  the  skin,  and  the  kidneys.  By  the  lungs  are  eliminated 
chiefly  carbon  dioxide  and  some  water,  by  the  kidneys  urine  (which 
is  a  weak  aqueous  solution  of  urea,  uric  acid,  urates,  phosphates, 
chlorides,  and  sulphates  of  calcium,  magnesium,  sodium,  potassium, 
etc.),  and  by  the  skin  are  constantly  eliminated  carbon  dioxide  and 
water,  and  during  the  process  of  sweating  also  more  or  less  of  the 
constituents  of  urine. 

1  An  excretion  consists  of  material  detrimental  to  the  organisms,  and  removed  from  it  by 
certain  glands.  A  secretion  contains  peculiar  compounds  especially  elaborated  by  the  glands 
for  the  purpose  of  serving  certain  requirements  of  the  organism  or  its  offspring.  Thus,  urea 
and  sweat  are  excretions,  while  pepsin  and  milk  are  secretions. 


ANIMAL  FLUIDS  AND  TISSUES.  649 

There  is  also  excretion  through  the  intestinal  tract. 

Chemical  changes  after  death.  After  the  death  of  either  a 
plant  or  an  animal,  a  chemical  decomposition  commences  which  finally 
results  in  the  formation  of  those  inorganic  compounds  from  which 
the  plant  originally  derived  its  food,  viz.,  carbon  dioxide,  water, 
ammonia,  sulphates,  phosphates,  etc.  This  decomposition  of  a  dead 
body  is  generally  a  simultaneous  fermentation  or  putrefaction,  aided 
by  decay  or  slow  combustion. 

There  are  numerous  intermediate  products  formed,  which  differ 
according  to  the  nature  of  the  decomposing  substance,  or  according 
to  the  conditions  (degree  of  temperature,  amount  of  moisture  and  air 
present,  etc.)  under  which  the  decomposition  takes  place. 

During  the  decomposition  of  dead  vegetable  matter  (especially  of 
moist  wood)  the  intermediate  products  are  frequently  called  humus, 
which  substance  (or  better,  mixture  of  substances)  forms  the  chief 
part  of  the  organic  matter  in  the  soil. 

During  the  decomposition  of  dead  animals,  the  sulphur  is  first 
eliminated  as  hydrogen  sulphide,  and  a  number  of  other  intermediate 
products  have  been  shown  to  be  formed ;  among  them  certain  organic 
bases  called  ptomaines  or  cadaveric  alkaloids,  substances  which  have 
been  spoken  of  in  Chapter  52.  The  decomposition  of  organic  matter 
may  be  prevented  under  conditions  which  have  been  mentioned  here- 
tofore in  connection  with  putrefaction. 

55.   ANIMAL   FLUIDS   AND   TISSUES. 

Constituents  of  the  animal  body.  The  animal  body  consists 
mainly  of  three  kinds  of  matter,  viz.,  water,  organic,  and  inorganic 
matter.  It  contains  of  water  about  70  per  cent.,  of  organic  matter 
25  per  cent.,  and  of  inorganic  matter  about  5  per  cent.  The  water 
may  be  determined  by  drying  a  weighed  quantity  in  an  air-bath  at  a 
temperature  of  100°  to  105°  C.  (212°-221°  F.);  the  organic  matter 
is  estimated  by  burning  the  dried  substance,  and  the  inorganic  matter 

QUESTIONS. — What  is  the  difference  between  vegetable  and  animal  life  from 
a  chemical  point  of  view  ?  Mention  the  chief  substances  serving  as  plant  food. 
Explain  the  formation  of  organic  substances  in  the  plant.  What  elements 
enter  into  the  animal  system  as  necessary  constituents?  The  members  of  which 
three  groups  of  organic  substances  are  chiefly  used  as  food  by  animals?  Give 
a  full  explanation  of  respiration.  Explain  the  term  calorie,  and  state  the  use 
made  of  it  in  valuation  of  food.  Which  points  should  be  considered  in  the 
selection  of  a  diet?  What  are  the  waste  products  of  animal  life,  and  through 
which  channels  are  they  eliminated?  What  is  the  final  result  of  the  decom- 
position of  dead  plants  or  animals  ? 


650  PHYSIOLOGICAL   CHEMISTRY. 

(ash)  by  weighing  the  residue.  Some  of  the  elements  which  are  left 
in  the  inorganic  residue  have,  however,  been  actually  constituents  of 
organic  compounds ;  iron,  for  instance,  wrhich  is  left  in  the  ash,  has 
been  chiefly  a  constituent  of  haemoglobin  ;  sulphur,  left  as  a  sulphate, 
may  have  been  a  constituent  of  albumin,  etc. 

The  complex  nature  of  the  various  organic  matters  has  been  referred 
to  in  the  preceding  chapter,  and  will  be  more  fully  considered  below; 
but  it  may  be  mentioned  here,  that  some  of  these  organic  substances 
(or  groups  of  substances)  may  be  separated  by  a  successive  treatment 
of  the  animal  matter  with  various  solvents.  Thus,  by  treating  with 
ether  or  carbon  disulphide,  all  fats  may  be  extracted  ;  by  then  treat- 
ing with  alcohol  and  water  successively  other  substances  (generally 
termed  extractive  matter  or  extractives)  are  dissolved,  which  may  be 
obtained  by  evaporating  the  solution. 

The  relative  quantities  of  the  three  constituents  in  some  of  the 
animal  fluids  and  tissues  is  shown  in  the  following  table : 


Water. 

Organic  and 
volatile  matter. 

Inorganic  resi- 
due (ash). 

Saliva    .... 

.     99.50 

0.32 

0.18 

Gas  trie  juice 

.     9943 

0.33 

0.24 

Pancreatic  juice    . 

.     90.97 

8.18 

0.85 

Bile       .... 

85.92 

13.30 

0.781 

Chyle    .... 

.     91.80 

7.40 

0.80 

Lymph 

.     91  80 

7.40 

0.80 

Pus        .... 

.    87.00 

12.20 

0.80 

Cows'  milk    . 

.    87.00 

12.25 

0.75 

Human  milk 

.    86.80 

12.85 

0.35 

Blood    .         .         .         . 

.    79.50 

19.70 

0.80 

Blood-  corpuscles  . 

.    54.60 

44.68 

0.72 

Blood-  serum 

.    90.50 

8.68 

0.82 

Urine    . 

.     95.70 

3.00 

130 

Bone  (varies  widely)     . 

.     22.00 

26.00 

52.00 

Dentine 

.     10.00 

2500 

6500 

Enamel 

0.40 

3.60 

96.00 

Among  the  extractives  are  found  creatine  and  creatinine,  urea,  uric 
acid,  organic  salts,  etc.  After  the  fatty  matter  and  the  extractives 
have  been  removed  there  remains  an  elastic  and  somewhat  horny 
mass,  which  consists  chiefly  of  proteins  (albumin,  fibrin,  globulin,  etc.). 

The  complete  separation  of  all  substances  is  extremely  difficult  on 
account  of  the  great  similarity  in  properties  of  many  of  these  sub- 
stances, and  the  rapid  changes  which  they  suffer  when  acted  upon  by 
solvents  or  chemical  agents. 

As  the  nature  or  composition  of  many  of  the  inorganic  salts  present 
in  the  animal  tissues  is  changed  during  the  burning  off  of  the  organic 

1  The  metals  in  combination  with  the  biliary  acids  are  not  included. 


ANIMAL  FLUIDS  AND   TISSUES.  651 

matter,  it  is  necessary  to  determine  them  either  in  the  aqueous  solution 
(extract)  or  by  subjecting  the  animal  matter  to  dialysis,  by  which  process 
they  may  be  more  or  less  completely  separated  from  the  organic  matter, 
which  is  left  in  the  dialyzer,  while  the  salts  pass  through  the  membrane. 

Blood.  Two  kinds  of  blood  are  distinguished,  the  arterial  or  oxi- 
dized and  the  venous  or  deoxidized  blood.  Arterial  blood  as  it  is 
present  in  the  system,  or  immediately  after  it  has  been  drawn  from 
the  body,  is  a  red  liquid  of  an  alkaline  reaction  and  a  specific  gravity 
of  about  1.055.  Upon  examination  under  the  microscope  blood  is 
seen  to  consist  of  a  colorless  fluid,  called  plasma,  in  which  float  small 
globules  or  corpuscles,  which  make  up  about  40  per  cent,  of  the  whole 
volume  of  blood.  These  corpuscles  are  of  three  varieties,  viz.,  red 
and  white  corpuscles,  and  blood-plates.  The  red  corpuscles  of  blood, 
or  erytkrocytes,  which  give  to  the  blood  its  color,  are  biconcave,  cir- 
cular, non-nucleated  disks,  about  ^W  of  an  inch  in  diameter.  When 
viewed  through  the  microscope  they  are  of  a  faint  greenish-yellow 
color,  while  en  masse  they  show  the  color  of  arterial  blood.  The 
white  corpuscles  of  blood,  or  leucocytes,  are  round  or  irregularly  shaped 
nucleated  cells ;  they  are  devoid  of  coloring-matter,  and  are  far  less 
numerous  than  the  red  corpuscles.  The  blood-plates  are  colorless, 
oval,  round,  or  lenticular  disks,  measuring  generally  less  than  one- 
half  of  the  diameter  of  red  corpuscles. 

Specific  gravity.  This  varies  in  healthy  adults  between  1.046  and 
1.067,  but  under  pathological  conditions  may  vary  between  1.025 
and  1.068. 

The  specific  gravity  can  be  determined  by  permitting  a  drop  of  blood  to  fall 
into  a  mixture  of  chloroform  and  benzol  presenting  a  specific  gravity  of  about 
1.055.  If  the  drop  sinks  to  the  bottom,  more  chloroform  must  be  added  ;  if  it 
floats  on  the  surface,  benzol  has  to  be  added  until  it  floats  midway  in  the 
liquid.  The  specific  gravity  of  the  mixture,  which  is  now  identical  with  that 
of  the  blood,  is  determined  by  a  delicate  hydrometer. 

Reaction.  The  alkaline  reaction  of  blood  is  due  to  the  presence 
of  sodium  bicarbonate,  NaHCO3,  and  disodium  phosphate,  Na2HPO4, 
both  of  which  have  a  weak  alkaline  reaction.  "While  blood  reacts 
alkaline  to  litmus,  it  is  neutral  to  phenol  phthalein,  and  according  to 
the  newer  concept  of  alkalinity  (an  excess  of  dissociated  hydroxyl 
ions  over  the  dissociated  hydrogen  ions  present)  it  is  nearly  neutral. 
For  clinical  purposes  it  is  still  regarded  as  alkaline,  and  the  extent 
of  this  alkalinity  to  litmus  or  lacmoid  has  some  importance.  There 
are  no  very  satisfactory  methods  of  titration.  That  one  most  used 
(Dare)  depends  upon  the  disappearance  of  the  spectrum  of  hsemo- 


652  PHYSIOLOGICAL  CHEMISTRY. 

globin  as  a  solution  of  blood  is  gradually  neutralized.  Tartaric  acid, 
2^^,  is  the  acid  used,  and  the  addition  of  acid  is  made  by  means  of  a 
specially  devised  pipette  until  the  two  absorption  bands  become  no 
longer  visible  through  the  spectroscope. 

The  alkalinity  of  the  blood  may  be  estimated  by  mixing  5  c.c.  of  freshly 
drawn  blood  with  about  45  c.c.  of  a  0.25  per  cent,  solution  of  ammonium 
oxalate  (which  prevents  coagulation)  and  titrating  this  mixture  with  a  |^  solu- 
tion of  tartaric  acid,  using  as  an  indicator  lacmoid  paper  soaked  in  a  concen- 
trated solution  of  magnesium  sulphate. 

For  clinical  purposes,  where  often  but  small  quantities  of  blood  are  avail- 
able, the  following  method  may  be  used.  The  blood  is  drawn  into  a  capillary 
pipette  up  to  the  mark  etched  on  the  stem;  the  pipette  is  next  tilted  to 
admit  a  bubble  of  air  into  the  bore,  and  then  —^  sulphuric  acid  is  drawn  in  to 
the  mark.  The  exactly  equal  volumes  of  blood  and  acid  thus  obtained  are 
transferred  to  a  watch-glass,  well  mixed,  and  a  drop  of  the  mixture  then 
tested  with  lacmoid  paper.  If  an  acid  or  alkaline  reaction  be  shown,  the 
operation  is  repeated  with  weaker  or  stronger  acid  until  the  resulting  mixture 
is  neutral. 

Odor.  The  peculiar  odor  of  blood,  differing  widely  in  different 
animals,  is  due  chiefly  to  the  presence  of  certain  volatile  fatty  acids. 
Addition  of  sulphuric  acid  renders  the  odor  more  distinct. 

The  composition  of  blood.  The  following  table,  taken  from  Howell, 
lists  the  more  important  constituents  of  blood-plasma  : 

f  Fibrin  ogen. 

I   Paraglobulin.  {  Euglobulin. 
Proteins.  -<  <-  Pseudoglobulm. 

Serum-albumin. 
[  Nucleo-protein. 
Fats. 
Sugar. 
Urea. 

Jecorin. 
Extractives.  ^   Glucuronic  acid< 

Lecithin. 
Cholesterin. 
Lactic  acid. 

Chlorides     "|         f  Sodium. 
Carbonates    I         j   Potassium. 
lts'   1   Sulphates      j  of  -j   Calcium. 

Phosphates   \         I   Magnesium. 

L  Iron, 
f  Internal  secretions. 

Enzymes.  {  ^Pas^ 
Enzymes  and  unknowns.  ^  Glycolase,  etc. 

I   Immune  bodies  (amboceptors). 
Complements. 
I  Opsonins. 


ANIMAL  FLUIDS  AND  TISSUES.  653 

The  proteins  of  blood-plasma.  There  are  three  important  proteins 
in  blood-plasma  :  serum-albumin,  serum -globulin  (paraglobulin),  and 
fibrinogen.  Of  the  other  proteins  described,  the  nucleo-protein  seems 
to  be  the  best  founded.  As  fibrinogen  is  directly  concerned  in  the 
clotting  of  blood,  it  will  be  described  in  that  connection.  The  albumin 
and  the  globulin  of  the  blood  are  typical  members  of  their  respective 
classes,  and  possess  all  the  qualifications  of  these  classes  and  of  pro- 
teins in  general.  They  are  found  together  also  in  the  lymph  and  in 
various  other  fluids  of  the  body.  There  is  some  evidence  that  the 
albumin  is  in  reality  made  up  of  two  or  three  different  albumins, 
while  the  globulin  can  be  divided  into  two  portions  by  fractional  pre- 
cipitation. Thus,  on  adding  saturated  ammonium  sulphate  solution 
to  plasma,  all  the  globulin  will  be  precipitated  before  the  sulphate 
solution  amounts  to  50  per  cent,  of  the  resulting  mixture.  The 
so-called  euglobulin  will  precipitate  between  28  and  36  per  cent, 
of  saturation  with  ammonium  sulphate,  and  the  pseudoglobulin 
between  36  and  44  per  cent.  Under  these  conditions  no  albu- 
min will  be  cast  down.  If,  however,  solid  ammonium  sulphate  be 
now  added  to  the  point  of  saturation,  all  of  the  albumin  will  be 
precipitated. 

Coagulation.  When  blood  leaves  the  body  and  is  allowed  to  stand 
a  while,  it  will  be  seen  that  the  entire  mass  has  coagulated — /.  e.,  has 
been  converted  into  a  semi-solid,  gelatinous  material  known  as  the 
blood-clot,  or  the  placenta  sanguinis.  Later  it  will  be  observed  that 
a  small  quantity  of  straw-colored  liquid,  known  as  the  blood-serum, 
appears  on  top  of  the  clot.  While  the  latter  shrinks  in  volume  the 
quantity  of  serum  increases,  the  clot  finally  floating  in  the  liquid, 
which  itself  ultimately  gelatinizes  in  consequence  of  the  coagulation 
of  the  serum-albumin.  Clot  consists  of  fibrin  holding  in  its  meshes 
blood-corpuscles,  which  may  be  removed  by  washing  the  clot  in  a 
stream  of  water. 

The  coagulation  of  blood  can  be  prevented  in  various  ways.  After 
the  injection  of  albumose  into  a  vein  of  a  dog  the  blood  does  not  coag- 
ulate on  leaving  the  body.  If  the  blood  be  drawn  directly  into  a  sat- 
urated solution  of  magnesium  sulphate,  in  the  proportion  of  3  to  1, 
or  into  a  solution  of  potassium  oxalate,  so  that  the  mixture  contains  at 
least  1  per  cent,  of  oxalate,  no  coagulation  takes  place.  The  plasma 
obtained  from  such  blood  is  known  as  peptone,  salt,  and  oxalate  plasma, 
respectively. 

Coagulation  of  blood  may  be  retarded  by  rapidly  cooling  it.  If 
the  blood  of  a  horse,  whose  blood  always  coagulates  slowly,  be  re- 


654  PHYSIOLOGICAL   CHEMISTRY. 

ceived  into  a  cold,  narrow  glass  cylinder,  and  allowed  to  stand  at 
0°  C.,  the  blood  may  be  kept  fluid  for  several  days.  The  corpuscles 
will  deposit  in  a  red  layer  from  the  plasma. 

It  may  readily  be  shown  that  the  clotting  of  blood  is  due  to  a 
change  of  some  kind  which  converts  the  soluble  protein  fibrinogen 
into  an  insoluble  form  called  fibrin.  Fibrinogen  is  one  of  the  globu- 
lins, it  coagulates  at  a  temperature  of  from  50°  to  60°  C.,  and  is  pre- 
cipitated by  half- saturation  with  sodium  chloride.  It  is  present  also 
in  lymph. 

It  is  well  known  that  the  clotting  of  fibrinogen  is  produced  by  an 
organic  substance  formerly  called  fibrin-ferment,  but  preferably  called 
thrombin,  as  it  is  probably  not  an  enzyme.  It  is  also  known  that  this 
thrombin  is  active  only  in  the  presence  of  calcium  salts ;  that  is,  that 
inactive  thrombin  (prothrombin  or  thrombogen)  is  changed  by  cal- 
cium into  the  active  form.  It  is,  however,  possible  to  remove  the 
calcium  from  activated  thrombin  without  impairing  its  activity ; 
therefore  the  calcium  does  not  enter  directly  into  the  conversion  of 
fibrinogen  into  fibrin. 

As  calcium  is  present  in  all  blood,  it  is  evident  that  in  cir- 
culating blood  either  prothrombin  must  not  be  present  as  such, 
or,  if  present,  its  activation  by  the  calcium  must  be  prevented  by 
some  antagonistic  substance  (antithrombin),  for  otherwise  clotting 
would  occur  within  the  blood-vessels,  which  does  not  happen  under 
normal  conditions.  Accordingly,  there  are  two  theories  to  explain 
these  facts. 

Morawitz  believes  that  in  order  to  convert  prothrombin  into  throm- 
bin, not  only  calcium  but  also  a  secondary  organic  substance  (throin- 
bokinase)  must  be  present,  and  that  this  thrombokinase  is  furnished 
to  blood  which  has  escaped  from  the  blood-vessels  by  the  injured 
leucocytes  and  platelets.  The  other  view,  to  which  Howell  inclines, 
is  that  prothrombin  is  transformed  into  thrombin  by  calcium  salts 
alone,  and  that  this  change  is  prevented  by  the  antithrombin  of 
the  circulating  blood,  and  that  when  the  blood  is  shed  the  injured 
cells  set  free  a  zymoplastic  substance  which  counteracts  the  anti- 
thormbin  and  leaves  the  calcium  free  to  convert  the  prothrombin 
into  thrombin. 

The  different  methods  of  preventing  the  clotting  of  blood 
are  to  be  explained  thus :  The  cooling  of  blood  probably  pre- 
vents the  formation  of  the  thrombokinase,  or  the  thromboplas- 
tic  substances,  by  preserving  the  cells  intact.  The  addition  of 


ANIMAL  FLUIDS  AND   TISSUES.  655 

oxalate  solution  removes  the  calcium  salts  by  precipitation.  The 
injection  causes  the  production  of  antithrombin  in  the  injected 
animal. 

Blood-serum  differs  from  plasma  only  in  containing  no  fibrinogen 
and  much  active  thrombin. 

Experiment  74.  (Separation  of  the  proteins  of  blood-plasma  and  of  blood-serum.) 

a.  Fibrinogen.     To  5  c.c.  of  salt  or  oxalate  plasma  add  an  equal  volume  of 
saturated  solution  of  sodium  chloride.     Fibrinogen  is  precipitated,  carrying 
with  it  the  prothrombin.     Filter  and  preserve  the  nitrate  for  the  separation  of 
albumin  and  globulin,  as  detailed  below. 

Dissolve  the  fibrinogen  and  protlirombiu  in  a  little  dilute  salt  solution,  add 
an  excess  of  calcium  chloride,  and  keep  the  mixture  at  40°  C.  for  a  few  minutes. 
Shreds  of  fibrin  are  formed  and  precipitated. 

b.  To  25  c.c.  of  blood-settim,  contained  in  a  mortar,  add  20  grammes  of 
ammonium  sulphate  and  rub  with  a  pestle  until  the  fluid  is  saturated  with 
the  salt.     Filter  through  dry  filter-paper,  acidulate  the   filtrate  with   acetic 
acid,  and  boil.     No  change  occurs,  as  both  proteins  have  been  precipitated 
completely. 

c.  To  25  c.c.  of  blood-serum  add  25  c.c.  of  a  saturated   solution   of  am- 
monium sulphate;   filter;    and  wash  with  a  saturated  solution   of  the  salt. 
Under  this  treatment    only   serum-globulin    is    precipitated,   while    serum- 
albumin   is  kept  in  solution.     Heat  the  filtrate  to  boiling:    serum-albumin 
is  coagulated.      Place  some  of  the  residue  left  on  the  filter  (globulin)  in  a 
test-tube  and  pour  water  on  it;  the  protein  dissolves  by  virtue  of  the  small 
quantity  of  salt  adhering  to  it.     Heat  the  solution  to  boiling :    coagulation 
takes  place. 

d.  Saturate  25  c.c.  of  serum  with  magnesium  sulphate :  serum-globulin  is 
precipitated,  serum-albumin  remains  in  solution. 

Serum-albumin  and  serum- globulin  give  the  ordinary  protein  reactions. 

A  quick  method  to  obtain  fibrin  is  to  stir  or  whip  blood  with  twigs  im- 
mediately after  it  has  been  shed.  Under  these  conditions  the  fibrin 
does  not  entangle  the  blood-corpuscles,  but  separates  as  a  stringy  mass, 
which  adheres  to  the  twigs  used  for  stirring.  The  remaining  part,  being 
made  up  of  the  corpuscles  suspended  in  the  serum,  is  designated  as  defibrin- 
ated  blood. 

Red  blood-corpuscles  when  wet  contain  of  water,  54.63  per  cent. ; 
haemoglobin,  41.1  per  cent.;  other  proteins,  3.9  per  cent.;  fats 
(chiefly  cholesterin  and  lecithin),  0.37  per  cent.  The  quantity  of 
water  in  corpuscles  varies  widely,  and  most  likely  ranges  in  healthy 
blood  from  76  to  80  per  cent.  Dried  corpuscles  contain  about  90 
per  cent,  of  haemoglobin. 

While  red  blood-corpuscles  can  be  broken  up  (laked)  by  the 
addition  of  various  substances  to  the  blood,  the  simplest  way  is  by 


656  PHYSIOLOGICAL   CHEMISTRY. 

the  addition  of  water,  which  reduces  the  osmotic  pressure  of  the 
plasma,  and  consequently  causes  the  salts  of  the  corpuscles  to  attract 
an  excess  of  water,  whereby  the  corpuscle  is  ruptured  and  its  con- 
stituents go  into  solution.  In  order  to  avoid  this  action  on  the  blood- 
cells  and  a  similar  action  on  the  tissue  cells,  it  is  customary  in  sur- 
gical procedures,  and  especially  in  intravenous  injections,  to  use  a 
solution  of  equal  osmotic  pressure  with  the  blood.  Such  a  solution 
is  the  "normal  salt  solution"  made  up  usually  of  0.9  per  cent,  sodium 
chloride  in  distilled  water,  which  is  the  simplest  solution  that  has 
been  found  to  have  no  very  deleterious  effect. 

Blood-pigments.  The  haemoglobins  or  blood-pigments  are  the 
chief  constituents  of  red  blood-corpuscles ;  they  contain  from  0.4  to 
0.6  per  cent,  of  iron,  and  show  a  slight  difference  in  composition  ; 
when  in  powder  form  they  all  have  a  blood-red  or  brick-red  color; 
they  all  crystallize,  but  not  with  equal  facility.  Hemoglobin  is  the 
substance  which  carries  oxygen  to  the  various  tissues,  as  described  in 
the  previous  chapter.  It  belongs  to  the  class  of  conjugated  proteins. 

Experiment  75.  Pour  some  freshly  drawn  venous  blood  into  four  volumes  of 
a  saturated  solution  of  sodium  sulphate  contained  in  a  vessel  which  stands  in 
ice ;  mix  and  set  aside  for  several  hours ;  no  coagulation  occurs  and  the  cor- 
puscles settle  to  the  bottom  of  the  vessel.  Pour  off  the  supernatant  liquid, 
collect  the  sediment  on  a  filter,  and  wash  it  first  with  cold  solution  of  sodium 
sulphate  and  then  with  water. 

Prepare  haemoglobin  from  these  corpuscles  as  follows :  agitate  the  collected 
mass  violently  with  small  quantities  of  ether  until  the  corpuscles  are  nearly 
dissolved  ;  allow  the  liquid  to  settle,  filter,  render  the  filtrate  slightly  acid  with 
acetic  acid,  and  add  alcohol  as  long  as  the  precipitate  first  formed  continues  to 
dissolve ;  cool  the  red  solution  to  0°  C.  (32°  F.)  for  several  hours,  when  crystals 
of  haemoglobin  will  form ;  collect  these  on  a  filter  and  wash  with  an  ice-cold 
mixture  of  alcohol  and  water. 

Hcemoglobin,  also  called  reduced  hcemoglobin,  occurs  only  in  small 
quantity  in  arterial  blood,  in  larger  quantity  in  venous  blood,  and  is 
almost  the  only  coloring-matter  in  the  blood  after  asphyxiation.  A 
solution  of  hemoglobin  has  a  most  remarkable  attraction  for  oxygen, 
with  which  it  enters  into  a  molecular  combination,  forming  oxyhazmo- 
globin.  The  power  of  hemoglobin  to  take  up  oxygen  depends  on 
the  iron  it  contains.  The  solution  of  oxy hemoglobin  will  give  up 
oxygen  to  reducing  agents  or  when  subjected  to  a  sufficiently  low 
oxygen  pressure.  It  is  due  to  this  property  of  the  oxyhernoglobin 
that  arterial  blood  gives  up  oxygen  to  the  tissue. 


ANIMAL  FLUIDS  AND   TISSUES.  657 

Mdhcrmogtobin  is  a  transformation-product  of  oxyhsemoglobin  found 
in  sanguinous  transudates  and  cystic  fluids ;  it  also  occurs  in  the  urine 
during  haematuria  and  haemoglobin uria;  and  in  the  blood  and  urine 
after  poisoning  with  potassium  chlorate,  amyl  nitrite,  alkali  nitrates, 
and  several  other  bodies. 

Hcemochromogen.  When  haemoglobin  is  acted  upon  by  acids,  alka- 
lies, etc.,  it  is  split  into  globin  (a  histone)  and  hsemochrornogen.  The 
latter  forms  only  about  ^V  of  the  haemoglobin  molecule,  contains  all 
of  the  iron  present,  and  consequently  the  group  to  which  the  oxygen 
is  attached  when  oxyhsemoglobin  is  formed.  In  the  presence  of 
oxygen  haemochromogen  is  rapidly  converted  into  haematin. 

Ilcematin.  Just  as  haemochromogen  is  split  from  haemoglobin, 
haematin  is  derived  from  oxyhaemoglobin.  It  is  a  comparatively 
simple  substance,  having  the  formula  C34H34N4FeO5.  It  is  found  in 
the  feces  after  hemorrhage  in  the  intestine,  and  also  after  a  diet  con- 
sisting largely  of  red  meats.  Haematin  has  been  found  in  urine  after 
poisoning  with  arsenetted  hydrogen.  Haematoporphyrin  (^H^N^Oj 
is  obtained  when  haematin  is  hydrolyzed. 

Haematoporphyrin  occurs  in  traces  in  normal  urine ;  it  is  found  in 
greater  quantity  in  urine  after  the  use  of  sulphonal.  Haematopor- 
phyrin  is  isomeric  with  the  bile-pigment  bilirubin,  and  a  pigment 
closely  resembling  urobilin  has  been  obtained  by  the  action  of  reduc- 
ing agents  on  haematoporphyrin.  It  is  noteworthy  that  this  substance 
does  not  contain  iron. 

Carbon  monoxide  haemoglobin  is  a  molecular  combination  of  one 
molecule  of  haemoglobin  and  one  molecule  of  carbon  monoxide.  The 
combination  is  stronger  than  that  between  oxygen  and  haemoglobin  and 
this  explains  the  poisonous  action  of  carbon  monoxide,  which  causes 
death  by  replacing  the  oxygen  of  the  blood.  A  similar  and  even 
more  stable  chemical  combination  is  formed  with  haemoglobin  by 
nitric  oxide. 

Carbon  dioxide  haemoglobin  (carbo-hwmoglobin).  Haemoglobin  has 
the  property  of  forming  an  unstable  compound  with  carbon  dioxide, 
the  CO2  is,  however,  not  attached  to  the  same  portion  of  the  molecule 
as  that  to  which  the  oxygen  (in  oxy haemoglobin)  is  attached.  Thus, 
the  presence  of  carbon  dioxide  does  not  prevent  the  absorption  of 
oxygen  by  haemoglobin,  which  is  in  great  contrast  to  the  action  of 
carbon  monoxide,  and  is  important  in  the  process  of  respiration. 

Spectroscopic  examination.    The  different  haemoglobins  are  distinguished 
chiefly  by  their  absorption -spectra.    In  the  following  description  the  violet  end 
of  the  spectrum  is  assumed  to  be  on  the  observer's  right. 
42 


658 


PHYSIOLOGICAL   CHEMISTRY. 


a.  Oxyh&moglobin.     Dilute  10  c.c.  of  blood  with  90  c.c.  of  water,  and  filter. 
Place  part  of  the  solution  in  a  glass  vessel  with  parallel  sides  and  examine 
with  a  spectroscope.      When  the   solution  is  so  concentrated  the  spectrum 
will  probably  be  entirely  shut  off  as  far  as  the  yellow  or  orange,  but  on  gradu- 
ally diluting  with  water  a  spectrum  is  finally  seen  which  shows  two  absorption  - 
bands  to  the  right  of  the  D  line.     The  right-hand  band  is  broader,  fainter,  and 
less  sharply  denned  than  the  other,  and  the  color  of  the  light  which  emerges 
from  the  left  limb  of  the  left  hand  is  yellow.     When  the  solution  is  further 
diluted  the  bands  disappear  simultaneously.     (Fig.  72,  a.} 

b.  Reduced  haemoglobin.     When  a  solution  of  oxy haemoglobin  is  treated  with 
a  reducing  agent  the  coloring-matter  loses  oxygen  and  is  changed  to  hsemo- 


FIQ.  72. 


Yellow 


Qreen 


Cyan-blue 


Absorption-spectra  of  blood  constituents,  a,  oxyhaemoglobin. 
6,  reduced  haemoglobin,  c,  methsemoglobin.  d,  haematine.  e, 
reduced  hsematine.  /,  hsematoporphyrin.  g,  carbon  monoxide 
haemoglobin. 

globin.  Stokes'  fluid  is  the  most  suitable  reagent  for  reducing,  and  is  prepared 
as  follows:  Dissolve  3  grammes  of  selected  crystals  of  ferrous  sulphate  in  cold 
water  and  add  a  cold  aqueous  solution  of  2  grammes  of  tartaric  or  citric  acid. 
Make  up  with  water  to  a  volume  of  100  c.c.,  and  immediately  before  using  add 
ammonia-water  until  the  precipitate  which  forms  at  first  is  redissolved. 

Prepare  a  solution  of  oxyhsemoglobin  which  will  show  the  characteristic  ab- 
sorption-bands. Allow  a  few  drops  of  Stokes'  fluid  to  flow  into  the  solution,  when 
its  color  changes  to  a  purple  or  violet,  and  the  spectrum  shows  a  single  broad 


ANIMAL  FLUIDS  AND  TISSUES.  659 

diffused  and  poorly  defined  band,  as  though  two  oxyhsemoglobin  bands  had 
gone  together  and  had  been  displaced  to  the  left  (Fig.  72,  6).  When  the  solu- 
tion is  agitated  with  air  its  color  changes  to  bright  red  and  the  spectrum  again 
shows  oxy haemoglobin. 

c.  Methcemoglobin.     To  a  dilute  solution  of  blood  add  a  drop  or  two  of  a 
freshly  prepared  10  per  cent,  solution  of  potassium  ferricyanide.     The  color  of 
the  solution  becomes  brown.    Add  just  enough  sulphuric  acid  to  give  a  slightly 
acid  reaction  and  examine  spectroscopically,  when  the  spectrum  is  seen  repre- 
sented in  Fig.  72,  c.     On  rendering  the  solution  slightly  alkaline  and  adding 
a  few  drops  of  Stokes'  fluid  the  methaenioglobin  changes  to  haemoglobin,  and 
on  agitating  with  air  into  oxyhsemoglobin.     These  changes  can  easily  be  fol- 
lowed with  the  spectroscope. 

d.  Add  hcematin.     To  a  few  drops  of  undiluted  blood  add  a  drop  or  two  of 
acetic  acid.     The  haemoglobin  is  broken  up  into  a  histon  called  globin,  and  a 
non-protein  substance  called  hsemin.     The  solution  which  results  is  almost 
black,  but  on  diluting  with  water  is  seen  to  be  red.    The  spectrum  has  a  band 
in  the  red,  almost  coincident  with  the  band  shown  by  methsemoglobin  in 
neutral  or  acid  solution. 

e.  Alkaline  hcematin.     To  a  portion  of  acid  hsematin  solution  add  sodium 
hydroxide  until  the  precipitate  which  forms  has  redissolved.     The  solution 
will  be  alkaline  and,  if  properly  diluted,  will  show  a  poorly  defined  band  to 
the  left  of  the  D  line.     It  is  usually  observed,  however,  that  the  entire  spec- 
trum is  absorbed  except  the  red.     (Fig.  72,  d.) 

f.  Reduced    hcematin   (Hsemochromogen).     Reduce  a  portion   of   alkaline 
haematm   solution  with  Stokes'   fluid,   and  after  properly  diluting  examine 
Bpectroscopically.     Two    sharply   defined    dark   bands   are   seen  between   D 
and  E,  which  seem  to  be  coincident  with  the  bands  produced  by  oxyhaemoglo- 
bin.     It  will  be-  noted,  however,  that  the  light  which  emerges  on  the  left  of  the 
left  band  is  plainly  green.     By  diluting  the  solution  with  water  the  band  on 
the  right  may  be  made  to  disappear,  while  the  other  band  is  still  very  dark. 
(Fig.  72,  e.) 

g.  Hcematoporphyrin.     Add  a  drop  of  blood  to  a  few  c.c.  of  concentrated 
sulphuric  acid,  mix  well,  dilute  with  water,  and  render  alkaline  with  sodium 
carbonate.     The  spectroscope  shows  four  bands.     (Fig.  72,  /.) 

h.  Carbon  monoxide  hcemoglobi?i.  Pass  a  slow  current  of  carbon  monoxide 
(illuminating-gas,  containing  carbon  monoxide,  may  be  used)  through  50  c.c. 
of  blood  until  its  color  is  bright  red.  Examined  spectroscopically,  the  bands 
seen  occupy  nearly  the  same  position  as  those  of  oxy haemoglobin,  but  they  do 
not  disappear  on  treatment  of  the  solution  with  Stokes'  fluid.  (Fig.  72.  g.) 

On  adding  to  10  c.c.  of  carbon  monoxide  haemoglobin  solution  15  c.c.  of  a 
20  per  cent,  solution  of  potassium  ferrocyanide  the  mixture  shows  a  bright-red 
color.  On  treating  oxyhsemoglobin  solution  in  the  same  way,  it  assumes  a 
grayish-brown  or  green  color. 

Examination  of  blood-stains.  Blood-stains  may  be  recognized, 
after  having  been  washed  off  with  as  little  water  as  possible,  by  the 
following  methods : 

1.  Examine  the  reddish  fluid  under  the  microscope  for  blood  cor- 
puscles. 


660  PHYSIOLOGICAL   CHEMISTRY. 

2.  Evaporate  a  drop  of  the  fluid  on  a  microscope   slide  with  a 
minute  fragment  of  sodium  chloride,  cover  with  a  cover-glass,  allow 
a  drop  of  glacial  acetic  acid  to  enter  from  the  side  and  warm  gently ; 
abundant  crops  of  hsemin  crystals  are  seen  under  the  microscope 
after  cooling. 

3.  Add  a  drop  of  the  fluid  to  some  freshly  prepared  tincture  of 
guaiacum  in  a  test-tube  and  float  on  the  surface  of  an  ethereal  solu- 
tion of  hydrogen  dioxide ;  a  blue  ring  forms  at  the  junction  of  the 
ethereal  solution  and  the  guaiacum.    (Blood  is,  however,  not  the  only 
substance  showing  this  reaction. 

4.  The  spectroscope  shows  bands  characteristic  of  haemoglobin. 

5.  The  biologic  blood-test.     This  test  depends  upon  the  fact  that 
animals  (rabbits)  injected  with  human  blood-serum  will  develop  a 
specific  antibody.     This  antibody  is  present  in  the  blood-serum  of 
the  injected  animal  and  is  termed  a  "  precipitin,"  because  it  produces 
a  visible  precipitate  when  the  serum  of  the  animal  is  mixed  with  a 
solution  of  human  blood-serum.     As  the  technique  is  very  intricate, 
and  the  results  are  worthless  unless  carefully  controlled,  no  details 
can  be  given  here.     Positive  results  can  be  obtained  with  blood  or 
blood-stains  many  years  old.     Human  protein  of  other  origin  (milk, 
semen,  etc.)  and  protein  from  the  higher  anthropoid  apes  will  also 
give  positive  results. 

The  immune  bodies  of  the  blood-serum.  When  foreign  protein 
is  introduced  into  an  animal  by  injection  or,  as  in  disease,  by  infection 
with  bacteria,  it  is  found  that  there  is  a  response  on  the  part  of  the 
animal  which  causes  the  presence  of  certain  substances  (immune 
bodies,  antibodies)  in  the  circulating  blood.  These  have  a  specific 
action  upon  the  foreign  protein.  To  this  class  belong  agglutinins, 
lysins,  etc.  Agglutinins  are  capable  of  causing  an  agglutination  or 
clumping  of  the  corresponding  bacteria.  They  have  proved  of  great 
clinical  value  in  the  diagnosis  of  typhoid  fever  by  means  of  the  Widal 
reaction.  This  test  consists  in  observing  microscopically  or  macro- 
scopically  a  mixture  of  active  typhoid  bacilli  and  the  blood-serum  of 
the  patient.  If  agglutinins  are  present,  and  the  bacteria  are  clumped 
within  a  certain  time  by  a  certain  dilution  of  serum,  it  is  shown  that 
the  patient  has,  or  in  some  cases  has  had,  typhoid  fever.  Bacterio- 
lysins  are  antibodies  capable  of  dissolving  the  corresponding  bacteria. 
Opsonins  are  capable  of  producing  some  change  in  bacteria,  whereby 
it  becomes  possible  for  the  leucocytes  of  the  blood  to  ingest  them 
(phagocytosis).  They  are  normally  present  in  varying  amounts.  It 
is  manifest  that  these  bodies  form  a  part  of  the  defensive  mechanism 


ANIMAL  FLUIDS  AND  TISSUES.  661 

of  the  body.  They  have  so  far  not  been  of  great  assistance  thera- 
peutically,  but  promise  to  be  of  great  value  in  the  prophylaxis  of 
certain  diseases,  as  in  the  typhoid  vaccination  by  injections  of  killed 
cultures  of  B.  typhosus. 

In  this  connection  it  is  important  to  note  that  bacteria  form  several 
classes  of  toxins  or  poisons.  Ptomaines  are  produced  by  the  effect 
of  bacteria  upon  the  medium  in  which  they  are  growing.  Bacterial 
toxins  are  substances  which,  in  distinction  to  ptomaines,  are  elab- 
orated by  the  bacteria  within  the  bacterial  cells.  These  are  substances 
of  doubtful  chemical  structure  and  are  divided  into  two  classes :  (1) 
Endotoxins,  toxins  existing  mainly  in  connection  with  the  bacterial 
cell,  going  into  solution  with  difficulty  and  possessing  in  such  solution 
only  a  moderately  poisonous  action.  (2)  Soluble  toxins,  readily  re- 
moved from  the  bacterial  cell  by  solution  and  giving  a  solution  of 
strong  toxic  action. 

It  has  been  found  that  an  animal  which  has  been  treated  with  bac- 
teria-producing soluble  toxins  has  present  in  its  blood  a  specific  anti- 
body which  is  capable  of  neutralizing  the  toxin  of  the  corresponding 
bacteria.  This  substance  is  called  an  antitoxin  and  protects,  from 
the  poisonous  effects  of  the  toxin,  not  only  the  original  animal  (active 
immunity),  but  also  other  animals  into  which  the  antitoxin-containing 
serum  may  be  injected  (passive  immunity).  This  production  of 
passive  immunity  has  been  widely  used  in  the  treatment  of  diphtheria 
and  the  prophylaxis  of  tetanus.  In  other  bacterial  diseases,  such  as 
typhoid  and  streptococcus  infections,  where  the  toxins  present  are 
mainly  endotoxins,  the  production  of  an  antitoxin  conferring  passive 
immunity  has  not  been  successful. 

In  the  case  of  some  of  these  antibody  reactions  it  is  found  that  a 
third  substance  is  necessary.  This  substance  is  commonly  called  the 
complement ;  and  in  this  connection  the  antibody  is  termed  the  am- 
boceptor, and  the  foreign  protein  the  antigen.  The  amboceptor  and 
the  complement  are  both  present  in  the  blood-serum.  Complement 
is  an  unstable  substance  present  in  all  fresh  blood,  and  is  not  specific, 
that  is,  it  will  enable  any  amboceptor  to  act  upon  the  corresponding 
antigen.  Amboceptor  is  fairly  stable,  is  usually  present  only  in  re- 
sponse to  the  introduction  of  some  antigen,  and  is  specific,  that  is,  it 
will  act  only  upon  its  corresponding  antigen. 

As  amboceptor  will  act  upon  antigen  only  in  the  presence  of  com- 
plement, the  presence  or  absence  of  complement  in  a  solution  may 
readily  be  shown  by  mixing  the  solution  with  a  suitable  amboceptor 
and  antigen,  when  the  presence  of  complement  is  shown  by  the  occur- 


662  PHYSIOLOGICAL   CHEMISTRY. 

rence  of  the  interaction  of  the  amboceptor  and  antigen,  while  its  ab- 
sence is  shown  by  the  failure  of  the  reaction.  The  reagents  com- 
monly used  are  red  blood-corpuscles  and  the  corresponding  haemolysin 
(amboceptor),  since  the  interaction  is  shown  by  a  visible  change, 
haemolysis,  and  if  no  reaction  occurs  the  mixture  remains  unchanged. 

This  procedure  is  used  in  the  Wassermann  reaction  for  syphilis. 
If  a  mixture  be  made  of  the  blood-serum  of  a  syphilitic  patient,  an 
emulsion  of  animal  lipoids,  and  complement,  it  is  found  that  the  com- 
plement becomes  absorbed  or  fixed,  so  that  if  the  mixture  be  tested 
for  complement  by  the  addition  of  red  blood-corpuscles  and  the  cor- 
responding haemolysin,  no  haemolysis  will  occur.  If,  on  the  other 
hand,  the  patient  has  not  syphilis,  no  fixation  of  complement  will 
occur,  the  complement  will  be  left  free  to  act,  and  will  produce  hae- 
molysis when  the  corpuscles  and  haemolysin  are  added. 

Ehrlich,  in  explaining  his  theory  of  immunity,  begins  by  describ- 
ing the  cell  as  consisting  of  a  certain  group  of  atoms  forming  an 
essential  nucleus  which  is  combined  with  several  different  groups  of 
atoms,  called  side-chains,  varying  in  composition  and  structure. 

Each  of  these  side-chains  has  atoms  arranged  in  such  a  way  that 
they  present  affinities  for  combining  with  groups  of  atoms  of  nutrient 
or  other  material  circulating  in  the  animal  fluids.  These  groups  he 
calls  receptors,  and  the  arrangement  of  atoms,  by  virtue  of  which 
combination  occurs,  a  haptophore  group. 

Thus,  specific  lysis  is  due  to  the  action  of  a  complement  on  a  spe- 
cific cell  through  a  specific  amboceptor,  the  chemical  reaction  being 
due  to  the  presence,  in  the  chemical  structure  of  the  cell,  of  a  re- 
ceptor having  a  group  of  atoms  haptophorous  with  a  group  of  atoms 
of  the  amboceptor,  which,  in  turn,  has  a  group  haptophorous  with  one 
of  the  complement. 

Lymph  is  a  clear,  colorless,  or  slightly  yellow  liquid  of  a  faint 
alkaline  reaction ;  in  composition  it  closely  resembles  blood-serum. 
It  contains  less  protein,  particularly  less  fibrinogen,  the  salts  and  ex- 
tractives are  present  in  about  the  same  amount.  Lymph  coagulates 
more  slowly  and  less  firmly  than  blood.  The  term  "  chyle  "  is  applied 
to  the  lymph  of  the  lacteals  and  thoracic  duct  when  it  is  clouded  by 
the  fat  absorbed  from  the  food  in  the  intestine. 

Bone  is  chemically  distinguished  from  other  tissues  by  the  large 
quantity  of  inorganic  salts  which  it  contains.  Dried  bones  contain 
about  31  per  cent,  of  organic  matter  combined  with  69  per  cent,  of 
mineral  matter.  Different  bones  (and  even  different  parts  of  the  same 


ANIMAL  FLUIDS  AND   TISSUES.  663 

bone)  of  the  same  person  differ  somewhat  in  composition ;  more- 
over, the  bones  of  a  child  contain  somewhat  more  of  organic  matter 
than  those  of  a  grown  person,  as  may  be  shown  by  the  following 
analyses  of  the  corresponding  bone  in  children  and  a  grown  person : 

Child  one  year.  Child  five  years.  Man  twenty-five  years. 

Organic  matter,  43.42  per  cent.  32.29  per  cent.  31.17  per  cent. 

Tricalcium  phosphate,  48.55         "  59.74        "  58.95         " 

Magnesium  phosphate,       1.00         "                1.34        "  1.30         " 

Calcium  carbonate,             5.79        "               6.00        "  7.08        " 

Soluble  salts,                       1.24        «  0.63        "  1.50        " 

Ferric  phosphate,                     Traces.                     Traces.  Traces. 

Frequently  human  bones  contain  calcium  fluoride,  which  substance, 
to  the  amount  of  1  to  2  per  cent.,  is  a  normal  constituent  of  the 
bones  of  many  animals.  The  organic  matter  of  bone  is  ossein,  a 
collagen,  yielding  gelatin  on  boiling  with  dilute  hydrochloric  acid. 

Experiment  76.  Pour  upon  3  grammes  of  bone  10  c.c.  of  water,  and  then 
10  c.c.  of  hydrochloric  acid.  (Notice  that  carbon  dioxide  is  liberated.)  The 
dilute  acid  dissolves  the  mineral  constituents  of  the  bone,  leaving  the  organic 
matter  (ossein)  as  a  swollen  mass,  which  retains  the  shape  of  the  bone. 

Decant  the  acid  solution,  and  to  part  of  it  add  an  excess  of  ammonia,  then 
acidify  with  acetic  acid.  The  greater  part  of  the  precipitate  formed  by  am- 
monia will  dissolve.  The  insoluble  part  contains  traces  of  silica,  but  is  chiefly 
ferric  phosphate,  most  of  which  is  derived  from  the  blood  in  the  bone.  Filter 
and  test  portions  of  filtrate  for  phosphoric  acid  with  ammonium  molybdate 
and  for  calcium  with  ammonium  oxalate.  Dissolve  the  washed  precipitate  on 
the  filter  with  a  little  hydrochloric  acid,  and  test  for  phosphoric  acid  as  above, 
and  for  iron  with  potassium  ferrocyanide.  (The  detection  of  the  mineral  con- 
stituents of  bone  may  be  carried  out  with  the  ash  left  from  incinerating  bone.) 

Wash  the  ossein,  obtained  above,  first  with  water,  then  with  dilute  solution 
of  sodium  carbonate,  and  finally  with  water  again.  Put  the  washed  ossein  in 
a  beaker  with  a  little  water  and  boil  until  most  of  the  ossein  has  been  dissolved. 
Neutralize,  if  necessary,  with  sodium  carbonate,  and  filter  while  hot  into  a  test- 
tube.  On  standing,  the  solution  gelatinizes  more  or  less  completely.  Ossein 
is  converted  into  gelatin  by  this  treatment. 

Gelatin.  The  purest  commercial  form  of  gelatin  is  known  as 
isinglass,  prepared  from  the  sounds  or  air-bladders  of  certain  fishes ; 
it  is  much  used  as  an  article  of  food  in  creams  and  jellies.  An 
impure  gelatin,  prepared  from  animal  refuse  (hoofs,  bones,  hides,  etc.), 
forms  common  glue,  and  its  solution  in  acetic  acid  is  sold  as  liquid 
glue.  In  a  pure  state  gelatin  is  a  colorless  or  slightly  yellowish, 
transparent,  tasteless  mass.  The  presence  of  gelatin  often  prevents 
the  formation  of  precipitates  by  holding  them  in  suspension  in  a 
finely  divided  state,  so  that  they  may  pass  through  filter-paper. 


664  PHYSIOLOGICAL  CHEMISTRY. 

The  nutritive  value  of  gelatin  is  discussed  under  Metabolism 
(page  646). 

As  gelatin  contains  no  tyrosiue  and  no  tryptophane,  it  will  be 
found  that  the  results  obtained  with  the  xanthoproteic  and  Mil  Ion 
tests  below  are  only  faintly  positive,  being  due  to  impurities. 

Tests  for  gelatin.  Pour  upon  a  gramme  of  gelatin  25  c.c.  of  water  and  allow 
to  stand  twenty-four  hours.  The  gelatin  now  is  swollen,  but  not  dissolved. 
Decant  the  water,  add  8  c.c.  of  distilled  water,  heat  over  a  water-bath  until  the 
gelatin  dissolves,  then  cool.  To  the  gelatinous  mass,  thus  obtained,  add  about 
50  c.c.  of  water  and  heat  again  until  dissolved.  Use  this  solution  for  the  fol- 
lowing tests : 

1.  Add  tannin,  or  hydrochloric  acid  and  phosphotungstic  acid:  voluminous 
precipitates  are  formed. 

2.  Boil  a  portion  with  one-third  its  volume  of  nitric  acid :  a  faint-yellow 
color  is  produced,  showing  the  presence  of  an  aromatic  radical. 

3.  Add   caustic  potash  and  a  little  cupric  sulphate :  a  blue  to  violet  color 
appears  without  a  trace  of  red.     (Difference  from  albumoses  and  peptones.) 

4.  Boil  with  Millon's  reagent:  a  faint  pink  or  red  color.     (Difference  from 
proteins  in  general.) 

5.  Add  bromine-water:  a  heavy  yellow  precipitate  is  formed,  possessing 
tough,  adhesive  properties. 

6.  Add  a  few  drops  of  acetic  acid  and  boil ;  add  acetic  acid  and  potassium 
ferricyanide ;  add  mercuric  chloride.     Precipitation  takes  place  in  neither  case. 
(Difference  from  simple  proteins.) 

Note  that  gelatin  solidifies  on  cooling  and  becomes  liquid  again  on 
the  application  of  heat  (difference  from  proteins  in  general). 

Teeth  consist  of  three  distinct  tissues,  viz.,  dentine,  forming  the 
chief  mass,  in  its  interior  being  the  pulp  cavity ;  enamel,  investing 
the  crown  and  extending  some  distance  down  the  neck ;  and  cement, 
covering  the  fangs.  The  composition  of  cement  is  almost  the  same  as 
that  of  bone,  its  organic  and  inorganic  constituents  having  the  rela- 
tive proportions  of  30  :  70. 

Dentine  contains  less  water  than  bone  and  is  also  poorer  in  organic 
matter.  The  following  table  gives  the  composition  of  the  dentine  of 
an  adult  woman  and  man  respectively : 

Woman.  Man. 

Organic  matter — ossein  and  vessels    .        .        .  27.61  20.42 

Calcium  phosphate 66.72  67.54 

Calcium  carbonate 3.36  7.97 

Magnesium  phosphate 1.08  2.49 

Soluble  salts,  chiefly  sodium  chloride        .         .  0.83  1.00 

Fat 0.40  0.58 

Enamel  is  distinguished  by  the  very  small  proportion  of  water  and 


ANIMAL  FLUIDS  AND   TISSUES.  665 

organic  matter  contained  in  it.     Its  average  composition  may  be  thus 
stated : 

Water  and  organic  matter 3,5 

Calcium  phosphate  and  traces  of  fluoride      ....  86.9 

Magnesium  phosphate 1.5 

Calcium  carbonate         ........  8.0 

Tartar  is  the  name  given  to  the  substance  which  deposits  from 
alkaline  saliva  on  the  teeth.  It  is  of  a  grayish,  yellowish,  or  brown- 
ish color,  and  consists  chiefly  of  calcium  phosphate,  with  a  little 
carbonate,  but  contains  also  bacteria  and  other  organic  matter,  salts 
of  the  alkalies,  and  silica. 

Hair,  nails,  horns,  hoofs,  feathers,  epithelium,  are  nearly  iden- 
tical in  composition.  They  all  contain  cholesterin  and  nitrogenous 
substances  termed  keratins,  which  are  probably  not  distinct  chemical 
compounds,  but  mixtures  of  several  substances  similar  in  composition 
and  properties. 

Cholesterin  fats  are  very  resistant  to  the  action  of  putrefactive  bacteria,  and 
the  occurrence  of  these  fats  in  combination  with  the  keratins  serves  as  a  pro- 
tection to  the  skin  surface  from  the  attacks  of  the  ever-present  bacteria. 

Muscle.  The  chemical  composition  of  the  various  morphological 
elements  of  striated  muscle  is  not  definitely  known.  Fresh,  inactive 
muscle  has  an  amphoteric  reaction — i.  e.,  it  colors  red  litmus-paper 
faintly  blue,  and  blue  litmus-paper  slightly  red.  After  activity  or 
death  the  reaction  becomes  acid.  If  the  blood  is  removed  from 
muscle  immediately  after  death,  and  the  muscle  is  then  quickly  cut 
and  frozen,  an  alkaline  fluid  can  be  pressed  out,  the  muscle-plasma, 
which  contains  the  proteins  of  muscle.  Muscle-plasma  coagulates 
spontaneously,  separating  a  protein  body,  myosin,  and  yielding  a 
serum,  muscle-serum.  A  similar  change  takes  place  in  the  muscle 
shortly  after  death,  causing  the  hardening  of  the  muscle  observed  in 
rigor  mortis. 

The  more  important  constituents  of  muscle  are  considered  here 
without  attempting  a  morphological  distinction. 

Proteins  of  muscle.  There  is  at  present  no  generally  accepted  view 
as  to  the  nature  of  the  essential  proteins  of  muscle  tissue.  This  is 
due  largely  to  the  many  different  names  given  them,  which  are  in 
almost  hopeless  confusion.  It  seems  certain  that  there  are  at  least 
two  proteins  in  living  muscle  which  have  the  power  of  coagulating 
after  death.  V.  Fiirth  calls  the  less  abundant  of  these  myosin  and 
its  coagulated  form  myosin  fibrin ;  the  second  he  calls  myogen,  and 


666  PHYSIOLOGICAL   CHEMISTRY. 

says  that  it  is  converted  first  into  an  intermediate  stage,  and  finally 
into  myogen  fibrin.  Myosin  belongs  to  the  globulins  and  myogen 
resembles  the  albumins.  The  coagulation  of  these  proteins  appears 
to  take  place  spontaneously,  as  no  enzyme  has  been  satisfactorily 
demonstrated.  The  process  is  probably  not  analogous  to  the  clotting 
of  fibrinogen. 

Carbohydrates  of  muscle.  There  are  present  in  muscle  varying 
amounts  of  dextrose  and  glycogen,  which  form  probably  the  most 
important  source  of  energy  for  the  work  of  the  muscle.  The  dex- 
trose is  brought  by  the  blood-stream,  and  any  excess  over  the  amount 
needed  for  immediate  use  is  converted  into  glycogen  by  the  muscle, 
and  "is  held  in  reserve  in  this  form.  When  a  muscle  does  work,  i.  e., 
when  it  contracts,  the  glycogen  is  split  again  into  dextrose,  which  is 
then  oxidized  with  a  resulting  liberation  of  energy.  It  is  possible  to 
show  that  the  carbon  dioxide  of  the  muscle  is  increased  in  amount, 
and  that  there  is  also  a  formation  of  lactic  acid.  It  is  believed  that 
this  lactic  acid  represents  an  incomplete  oxidation  of  the  sugar.  In 
the  burning  of  dextrose  by  the  muscle  tissue,  an  internal  secretion  or 
hormone  produced  by  the  pancreas  is  believed  to  play  an  important 
part. 

Muscle  extractives.  The  extractive  bodies  of  the  muscle  are 
important,  and  are  both  nitrogenous  and  non-nitrogenous.  Among 
the  first,  creatine,  the  xanthine  bases,  urea,  and  uric  acid  deserve  men- 
tion. Non-nitrogenous  extractives  always  present  are  inosite,  gly- 
cogen, sugar,  and  lactic  acid. 

Creatine  (Meihyl-guanidine-acetic  acid),  NH  =  ^\TC/ip2TT  \  p  TT  o 

=C4H9N3O2,  occurs  in  muscles  of  vertebrates,  in  the  brain,  blood, 
transudates,  and  the  amniotic  fluid.  When  pure,  it  forms  colorless, 
transparent,  rhombic  prisms.  The  crystals  are  soluble  in  75  parts 
of  cold,  much  more  soluble  in  hot  water,  slightly  soluble  in  alcohol, 
insoluble  in  ether.  The  solution  is  neutral  to  litmus,  though  creatine 
is  a  weak  base,  combining  with  some  of  the  acids  to  form  crystal- 
line salts.  Creatine  may  be  obtained  by  the  action  of  cyanamide  on 
sarcosine  (methyl-glycocoll). 

dride  of  creatine,  and  may  be  obtained  by  boiling  creatine  with  acids, 
when  a  molecule  of  water  is  split  off.  Vice  versd,  creatinine  may 
be  converted  into  creatine.  Creatinine  is  readily  soluble  in  water 
and  alcohol,  but  nearly  insoluble  in  ether ;  it  crystallizes  in  colorless 


ANIMAL  FLUIDS  AND   TISSUES.  667 

prisms ;  the  solution  is  slightly  alkaline  to  litmus.  Creatinine  is  a 
strong  base,  forming  well-defined  salts ;  it  also  forms  an  insoluble 
double  compound  with  zinc  chloride,  for  which  reason  the  latter  is 
often  used  to  precipitate  creatinine.  The  occurrence  of  creatinine 
in  urine  will  be  considered  later. 

Experiment  77.  a.  Preparation  of  creatine.  Digest  400  grammes  of  finely 
divided  lean  beef  with  500  c.c.  of  water  at  a  temperature  of  50°  C.  (122°  F.)  ; 
filter  the  mass  through  cloth,  press  out  well,  and  repeat  the  operation  twice 
with  1000  c.c.  of  water,  bringing  the  mixture  to  the  boiling-point  each  time ; 
then  evaporate  the  mixed  filtrates  to  about  one  liter.  (In  place  of  the  liquid 
extract,  thus  obtained,  a  solution  of  commercial  extract  of  beef  may  be  used.) 
Acidify  the  solution  with  acetic  acid,  heat  to  boiling,  and  filter  off  the  coagu- 
lated proteins  ;  to  the  cold  filtrate  add  basic  lead  acetate  as  long  as  a  precipitate 
is  formed,  filter  and  precipitate  excess  of  lead  by  passing  hydrogen  sulphide 
through  the  solution.  Finally  filter,  evaporate  filtrate  over  a  water-bath  to  a 
syrup,  and  set  aside.  After  a  day  or  two  crystals  of  creatine  will  be  found, 
which,  if  too  highly  colored,  may  be  redissolved  in  water,  decolorized  with 
bone-black,  and  recry stall ized. 

b.  Conversion  of  creatine  into  creatinine.  Heat  0.5  gramme  of  creatine  with 
10  c.c.  of  dilute  sulphuric  acid  for  half  an  hour  over  a  water-bath ;  then  dilute 
with  25  c.c.  of  water  and  add  a  sufficient  quantity  of  powdered  barium  car- 
bonate to  neutralize  the  acid.  Next  filter,  evaporate  the  filtrate  to  about  5  c.c., 
and  use  this  solution  of  creatinine  for  the  following  tests : 

1.  To  a  few  drops  of  the  solution  add  an  equal  volume  of  an  alcoholic  solu- 
tion of  zinc  chloride.     Creatinine  zinc  chloride,  (C4H7N3O)2.ZnCla,  crystallizes 
in  warty  lumps,  composed  of  fine  needles  or  prisms. 

2.  Weyl's  reaction.     Add,  drop  by  drop,  a  freshly  prepared,  dilute  solution 
of  sodium  nitroprusside,  Na2Fe(CN)5lSTO,  until  the  solution  is  colored  yellow; 
then  add  drop  by  drop  a  dilute  solution  of  sodium  hydroxide :  a  fine  transient 
ruby-red  color  is  obtained  which  soon  passes  into  yellow.     Acidulate  solution 
with  acetic  acid  and  warm :  solution  turns  green,  then  blue,  the  color  being 
due  to  the  formation  of  Prussian  blue. 

3.  To  a  very  dilute  solution  of  creatine  add  a  trace  of  an  aqueous  solution 
of  picric  acid  and  render  faintly  alkaline:  the  solution  turns  intensely  red. 

Xanthine  bases  are  a  group  of  nitrogenous  substances  produced  in 
the  organism  as  the  result  of  the  cleavage  of  nucleins.  They  are 
closely  related  to  one  another,  as  also  to  uric  acid,  from  which  they 
may  be  obtained  by  synthetic  processes.  Indeed,  an  increased  secre- 
tion of  uric  acid  follows  their  ingestion  as  food.  While  eleven 
xanthine  bases  have  been  isolated  from  the  cell,  only  four  (xanthine, 
hypoxanthine,  guanine,  and  adenine)  are  found  in  the  muscle.  Con- 
jointly the  xanthine  bases  are  also  termed  alloxur  bases  or  purine 
bases.  The  first  named  refers  to  the  fact  that  the  nucleus  of  xanthine 
bases  is  assumed  to  be  made  up  of  the  carbon-nitrogen  nuclei  of 
alloxsm,  C4H2N2O4  (an  oxidation-product  of  uric  acid),  and  wea, 


668  PHYSIOLOGICAL  CHEMISTRY. 

CN2H4O.  When  the  two  nuclei  occur  joined  together  into  one 
nucleus  the  latter  is  known  as  the  purine-nueleus.  Purine  itself  is  a 
hypothetical  compound  containing  this  nucleus. 


N— C 


C 

u 


N/~1  XT /""I  TT 

— O  JN  =Url 

II  II 

Nx                   C     C— N.  HC     C— NH. 

'             U->:  1J-N>H- 


Alloxan       Urea  Purine 

nucleus,    nucleus.  nucleus. 


By  oxidation,  or  by  replacement  of  hydrogen  atoms  in  purine  with 
the  radicals  OH,  NH2,  NH,  or  by  introducing  the  methyl  group, 
CH3,  the  different  purine  bases  or  allied  compounds  have  been 
formed.  These  bodies  are  also  closely  related  to  the  vegetable  bases 
caffeine  and  theobromine,  and  also  to  uric  acid,  as  shown  in  the  fol- 
lowing table  : 


Purine 

Hypoxanthine  (oxypurine)        ....  C5H4N4O 

Xanthine  (di-oxy  purine)   .....  C5H4N4O2 

Uric  acid  (tri-oxy  purine)  .....  C5H4N4O3 

Heteroxan  thine  (methyl-xan  thine)  .         .         .  C5H3(CH3)N4Oj 
Paraxanthine  (dimethyl-xanthine)  \  . 

Isomeric  with  theobromine  /         '         '  M^CH^I^O, 

Caffeine  (trimethyl-xan  thine)    ....  C5H(CH3)3N4O2 

Adenine  (amino-purine)    .....  C5H3(NH2)N4 

Guanine  (amino-oxypurine)      ....  C5H3(NH2)N4O 

Carnine  (dimethyl-uric  acid)    ....  C5H2(CH3)2N4O, 

Uric  acid  and  the  xanthine  bases  take  up  water  and  yield  qualitatively  the 
same  decomposition-products  when  treated  with  fuming  hydrochloric  acid 
under  pressure,  viz.,  ammonia,  carbon  dioxide,  glycocoll,  and  formic  acid. 

Xanthine  and  hypoxanthine  (sareine)  occur  generally  together, 
though  in  small  quantities,  in  urine  and  in  almost  all  tissues.  In 
larger  quantity  they  are  found  in  the  meat-extracts.  When  pure 
these  bodies  are  colorless  powders,  almost  insoluble  in  water,  alcohol, 
and  ether.  With  acids  they  form  crystallizable  salts,  and  with  silver 
nitrate  double  compounds,  which  are  employed  in  the  separation  of 
the  bases  from  fluids. 

Phosphocarnic  acid  is  a  glyco-nucleoprotein,  occurring  in  muscle  ;  it  yields 
on  hydrolysis  succinic  acid,  carbon  dioxide,  phosphoric  acid,  a  carbohydrate, 
and  carnic  acid,  a  protein  almost  identical  with  peptone.  It  forms  soluble 
compounds  with  the  alkaline  earths,  and  also  an  iron  compound  (carniferrin) 
soluble  in  alkalies  ;  these  properties  serve  as  a  means  to  carry  these  metallic 
compounds  through  the  body.  (Lacto-phosphocarnic  acid  is  an  analogous 
compound  found  in  milk.) 


ANIMAL  FLUIDS  AND   TISSUES.  669 

Muscle  pigment.  Muscle,  even  when  completely  freed  from  blood,  has  a  red 
color,  due  to  a  pigment  which  is  some  slight  modification  of  blood  haemoglobin. 

Of  non-nitrogenous  bodies  found  in  muscle,  inosite  and  sarcolactic  acid,  which 
have  been  previously  considered,  deserve  mention. 

Experiment  78  (Preparation  of  sarcolactic  add).  Dissolve  20  grammes  of 
commercial  meat-extract  in  200  c.c.  of  water,  add  basic  lead  acetate  as  long  as 
a  precipitate  is  formed ;  filter  and  evaporate  filtrate  to  a  syrupy  consistence. 
Then  add  200  c.c.  of  96  per  cent,  alcohol ;  filter  and  evaporate  the  filtrate  to 
dry  ness  over  a  water-bath.  Dissolve  the  residue  in  40  c.c.  of  water  and  20  c.c. 
of  sulphuric  acid.  Extract  this  solution  twice  with  an  equal  volume  of  ether 
in  a  separatory  funnel.  Filter  the  ethereal  solutions  and  evaporate  the  ether 
with  proper  precautions.  The  residue,  consisting  of  a  colorless  liquid,  is  sar- 
colactic acid,  to  which  apply : 

Uffelmann's  test  for  lactic  acid.  To  an  aqueous  solution  add  a  few  drops  of 
Uffelmann's  reagent  (10  c.c.  of  a  2  per  cent,  solution  of  carbolic  acid  in 
water,  to  which  a  few  drops  of  ferric  chloride  solution  have  been  added).  A 
yellow  color  is  produced. 

Inorganic  constituents  of  muscle  are  chiefly  mono-  and  dipotassium 
phosphate,  with  smaller  portions  of  sodium  bicarbonate,  salts  of 
magnesium  and  calcium,  some  iron  salts,  and  traces  of  sulphates 
and  chlorides. 

Meat- extracts  are  of  two  kinds,  those  from  which  the  proteins  and  peptones 
have  been  removed,  and  those  containing  besides  proteins  large  quantities  of 
the  basic  extractives.  Articles  of  the  first  class  are  destitute  of  nutritive 
value,  and  the  second  derive  no  nutritive  value  from  the  extractive  con- 
stituents. The  physiological  effect  of  the  flesh  bases  seems  to  be  in  the  direc- 
tion of  nerve  stimulants,  and  for  this  reason  they  are  to  be  classed  with  tea 
and  coffee  as  adjuncts  to  food,  not  as  true  foods. 

The  thyroid  gland  contains  iodine  in  some  form  of  protein  com- 
bination, known  as  thyro-iodine ;  this  compound  contains  9.3  per 
cent,  of  iodine. 

Desiccated  thyroid  glands,  Glandulae  thyroideae  siccae.  Numerous 
extracts  of  the  thyroid  are  upon  the  market.  The  preparation  of  the  Pharma- 
copoeia is  the  cleaned,  dried,  and  powdered  glands  of  the  sheep,  freed  from  fat. 
It  is  a  yellowish  amorphous  powder,  partially  soluble  in  water. 

Thyreoidectin  and  rodagen  are  unofficial  preparations  prepared  respectively 
from  the  blood  and  from  the  milk  of  animals  from  which  the  thyroids  have 
been  removed.  Their  action  is  stated  to  be  exactly  the  opposite  of  that  of  the 
thyroid  preparations. 

The  thyroid  gland,  and  also  the  adrenals,  have  some  influence  on  sugar 
metabolism,  which  is  not  yet  understood. 

The  suprarenal  glands  contain  a  substance  which  has  the  power  of  con- 
stricting the  blood-vessels  of  the  body,  and  thus  causing  a  great  but  transient 
rise  in  blood-pressure.  This  substance  has  been  found  to  be  methylamino- 
ethanol-dioxy-benzol,  C6H3(OH)2.CH(OH).CH2.NH.CH3.  It  is  used  particu- 


670  PHYSIOLOGICAL   CHEMISTRY. 

larly  to  produce  local  anaemia,  and  is  called  by  various  names :  suprarenalm, 
suprarenin,  adrenalin,  epinephrin. 

Desiccated  suprarenal  glands,  Glandulae  suprarenales  siccse.  These 
are  the  cleaned,  dried,  and  powdered  suprarenal  glands  of  the  sheep  or  ox, 
freed  from  fat.  A  light-yellowish,  amorphous  powder,  partially  soluble  in 
water. 

Brain  consists  of  so  many  individual  parts  that  the  analysis  of  it 
as  a  whole  is  of  little  value,  and  to  separate  these  parts  successfully 
is  a  task  not  yet  accomplished.  Brain,  as  a  whole,  contains  lecithin, 
cholesterin,  protagon,  and  many  other  substances,  some  of  which  are 
distinguished  by  the  large  quantity  of  phosphorus  they  contain. 

The  gray  matter  contains  albumin,  globulin,  nucleoprotein,  and  nuclein. 
Neurokeratin  forms  the  neuroglia.  In  the  white  matter  is  found  protagon,  a 
very  complex  substance  containing  nitrogen  and  phosphorus.  It  yields  on 
hydrolysis  a  lecithin,  fatty  acid,  and  cerebroside.  The  cerebrosides  are  nitro- 
genous substances  free  from  phosphorus,  yielding  on  hydrolysis  galactose, 
sometimes  called  brain-sugar.  Fused  with  caustic  potash,  or  boiled  with  nitric 
acid,  they  form  palmitic  or  stearic  acids.  Three  cerebrosides  are  known: 
cerebrin,  kerasin,  and  encephalin. 

The  term  "  lipoids :>  is  applied  to  an  indefinite  group  of  organic  substances, 
which  are,  like  the  fats,  soluble  in  ether  and  alcohol.  These  substances  are 
present  in  many  kinds  of  tissue,  and  are  particularly  abundant  in  the  brain 
and  in  nerve  fibres.  The  more  important  membranes  are  cholesterin  and  the 
phosphorized  fats  (phosphatides,  lecithins).  The  cerebrosides  are  also  classed 
here.  The  function  of  these  substances  is  entirely  unknown.  Their  abun- 
dance in  brain  tissue  is  the  basis  of  the  well-known  theory  that  the  anaesthesia 
produced  by  ether  and  chloroform  is  due  to  the  solvent  action  of  these  sub- 
stances upon  the  lipoids. 

Lecithins,  C^H^NPOg  or  C42H84NPO9.  Lecithin,  one  of  the  con- 
stituents of  bile,  is  a  member  of  the  group  of  substances  generally 
termed  phosphorized  fats  or  lecithins.  These  bodies  are  highly  com- 
plex in  composition,  and  may  be  looked  upon  as  fats  formed  f  Von/ 
glycerin-phosphoric  acid  by  substitution  of  hydrogen  atoms  with  two 
fatty  acid  radicals  and  a  base,  choline. 

Glycerin-phosphoric  acid,  C3H5<^  QpQ2QTj\     ^s  obtained  by  the 

action  of  glycerin  on  phosphoric  acid,  when  combination  takes  place 
with  elimination  of  water,  thus  : 

C3H5(OH)3     +    H3P04  C3H5(OH)2.H2P04    +    H2O. 

Glycerin-phosphoric  acid  is  a  syrupy  liquid  yielding  easily  soluble 
salts,  some  of  which  are  used  medicinally.  The  hydroxyl  hydrogen 
is  replaceable  by  acid  radicals  and  the  hydrogen  of  phosphoric  acid 
by  bases.  Thus,  by  introducing  the  radicals  of  stearic  acid  and 
of  choline  distearyl-lecithin  is  obtained  of  the  composition,  C3H5 
(C18H3502)2.HP04.C2H4N(CH3)3OH. 


ANIMAL  FLUIDS  AND   TISSUES.  671 

Choline  (Trimethyl-oxyetJiyl-ammonium  hydroxide),  N(CH3)3.C2H5O.OH,  has 
been  mentioned  as  one  of  the  ptomaines.  It  is  a  colorless  fluid  of  oily  con- 
sistency, has  strongly  basic  properties,  and  is  extremely  unstable.  By  removal 
of  the  elements  of  water  choline  is  converted  into  the  strongly  poisonous 
substance  neurine,  mentioned  on  page  620.  On  the  other  hand,  choline  by 
oxidation  is  converted  into  muscarine,  a  ptomaine  even  more  poisonous  than 
neurine. 

Cholesterin,  C27H45OH.  This  substance  has  been  classed  by 
physiologists  among  the  fats,  because  it  is  greasy  and  soluble  in 
ether,  but  its  chemical  constitution  is  that  of  an  alcohol.  It  is  found 
chiefly  in  bile,  but  also  in  blood,  nerve-tissue,  brain,  contents  of  the 
intestines,  feces,  etc. ;  its  presence  in  certain  vegetables,  as  pease, 
beans,  etc.,  has  also  been  demonstrated.  Cholesterin  combines  with 
fatty  acids  to  form  fats. 

Cholesterin  crystallizes  in  colorless,  rhombic  plates,  which  are 
insoluble  in  water,  alkalies,  and  dilute  acids,  but  soluble  in  ether.  It 
sometimes  forms  in  the  organism  solid  masses,  known  as  biliary  cal- 
culi or  gall-stones,  some  of  which  are  almost  pure  cholesterin. 

Cholesterin  is  an  unsaturated,  secondary  alcohol,  and  a  derivative 
of  the  terpenes. 

Reactions  of  cholesterin: 

1.  Place  a  small  quantity  of  cholesterin  on  a  slide,  moisten  with  a 
drop  of  80  per  cent,  sulphuric  acid,  and  cover  with  a  cover-glass. 
Allow  a  little  iodine  solution  to   run  in  under  the  cover-glass  and 
examine  it  with  the  microscope.     The  cholesterin  crystals  pass  through 
many  shades  of  colors,  gradually  becoming  brown  or  violet  or  clear 
blue. 

2.  Evaporate,  in   a  shallow  porcelain  dish,  a   small  quantity  of 
cholesterin  Avith  hydrochloric  acid  containing  a  trace  of  ferric  chloride. 
A  blue  residue  is  formed. 

QUESTIONS. — What  three  kinds  of  matter  are  found  as  constituents  of  the 
animal  body,  and  how  can  they  be  determined  quantitatively?  Mention  the 
chief  constituents  of  blood,  and  state  those  which  predominate  in  serum  and 
in  the  corpuscles  respectively.  What  substances  cause  the  clotting  of  blood, 
and  what  explanation  can  be  given  ?  How  may  blood-stains  be  recognized  ? 
What  are  the  characteristics  of  the  different  haemoglobins?  Describe  methods 
for  determining  the  specific  gravity  and  the  alkalinity  of  blood.  How  can  the 
proteins  of  blood-serum  be  separated  ?  Mention  the  principal  constituents  of 
muscles,  bone,  teeth,  and  hair.  State  the  properties  and  reactions  of  creatine 
and  gelatin.  What  is  the  composition  of  glycerin-phosphoric  acid,  and  in 
what  form  of  combination  does  it  exist  in  the  body? 


672  PHYSIOLOGICAL   CHEMISTRY. 

56.  DIGESTION. 

General  remarks.  It  has  been  stated  that  foods  are  divided  into 
two  classes,  inorganic  and  organic,  and  that  the  fetter  are  subdivided 
into  proteins,  carbohydrates,  and  fats ;  and  also  that  the  term  diges- 
tion refers  to  the  process  by  which  organic  foods  are  altered  in  such 
a  manner  that  they  may  be  absorbed. 

The  process  of  digestion  is  both  mechanical  and  chemical.  By 
the  mechanical  part  of  the  process  the  food-material  is  disintegrated, 
propelled  along  the  alimentary  canal,  and  mixed  with  the  different 
digestive  secretions.  These  latter  cause  a  chemical  change,  usually 
hydrolysis,  of  the  food,  converting  it  into  soluble  and  easily  absorb- 
able  substances.  For  convenience  of  study  the  process  is  divided 
into  salivary,  gastric,  and  intestinal  digestion ;  and  the  secretions 
and  chief  alterations  of  the  nutrients  in  these  portions  of  the  tract  are 
considered  separately.  It  should  be  remembered,  however,  that  these 
three  processes  are  closely  interdependent,  and  any  disturbance  of 
function,  mechanical  or  chemical,  in  one  part  of  the  digestion  will 
disturb  and  derange  all. 

Salivary  digestion.  The  first  part  of  the  process  of  digestion  is 
accomplished  in  the  mouth,  and  consists  in  the  breaking  up  of  the 
food  by  the  teeth  and  mixing  it  with  saliva,  the  process  being  known 
as  mastication.  In  addition,  the  saliva,  to  a  limited  extent,  converts 
starch  into  maltose.  This  action  of  the  saliva  is  due  to  its  ferment 
ptyalin.  Other  functions  of  the  saliva  are  to  keep  the  mucous  mem- 
brane of  the  mouth  moist  and  to  lubricate  the  food  bolus. 

Saliva  is  the  mixed  secretion  of  the  parotid,  submaxillary,  sub- 
lingual,  and  buccal  glands.  The  quantity  secreted  in  a  day  varies 
from  600  to  1500  c.c.  The  flow  is  easily  excited  by  reflex  stimula- 
tion, as  by  the  smell  or  sight  of  food,  or  by  chewing  of  some  insolu- 
ble substance.  Saliva  appears  as  a  viscid,  frothy,  tasteless,  inodor- 
ous liquid,  of  a  sp.  gr.  of  1.002  to  1.008.  The  reaction  to  litmus  is 
generally  slightly  alkaline,  but  may  become  acid  under  pathological 
conditions.  Saliva  as  it  appears  in  the  mouth  contains  food  particles 
and  numerous  micro-organisms.  The  average  composition  of  saliva 
is  as  follows : 

Water 99.49 

Mucin  and  epithelium 0.13 

Fatty  matter 0.11 

Ptyalin,  maltase,  and  other  organic  matter    .         .         .         .0.12 
Salts 0.15 

The  salts  are  alkali  and  earthy  phosphates,  carbonates  and  chlo- 
rides, and  potassium  sulphocyanate.  The  latter  occurs  in  variable 


DIGESTION.  673 

quantity  in  the  saliva  of  different  individuals.  Pathologically,  saliva 
may  contain  sugar  in  diabetes,  melanin  in  Addison's  disease,  bile- 
pigment  in  icterus.  Leucine  and  urea  have  been  found  in  saliva 
during  uremia.  The  iodides  and  some  other  drugs  are  habitually 
secreted  by  the  salivary  glands.  This  function  is  used  in  measuring 
the  rapidity  of  absorption. 

Ptyalin,  the  diastatic  enzyme,  occurs  in  the  saliva  of  all  animals 
except  the  pure  carnivora.  It  is  characterized  by  its  action  in  con- 
verting starch  into  sugar.  It  acts  best  at  40°  C.  (104°  F.)  in  a 
neutral  solution,  although  it  is  active  in  a  weak  alkaline  solution, 
and  also  in  acid  solution  up  to  0.2  per  cent,  of  mineral  acid. 

The  conversion  of  starch  into  sugar  by  ptyalin  is  a  progressive  hydrolysis. 
The  first  change  is  the  formation  of  soluble  starch,  which  gives  a  blue  color 
with  iodine.  Soluble  starch  is  split  into  maltodextrin  and  erythrodextrin  ;  the 
latter  gives  a  red  color  with  iodine.  These  dextrins  are  next  split  and  yield 
maltose,  maltodextrin,  and  achroodextrin,  which  are  not  colored  by  iodine. 
From  achroodextrin  more  maltodextrin  and  maltose  are  derived,  and  finally 
the  hydrolysis  results  in  the  formation  of  maltose  with  some  maltodextrin. 
The  maltose  is  converted  into  glucose  by  the  action  of  the  enzyme  maltase. 

Experiment  79.  Mix  intimately  1  gramme  of  starch  with  10  c.c.  of  water, 
pour  this  mixture  into  90  c.c.  of  boiling  water  and  stir  until  a  smooth  paste  is 
formed.  Place  10  c.c.  of  paste  in  a  test-tube,  heat  to  40°  C.  (104°  F.),  add  1 
c.c.  of  saliva  and  1  c.c.  of  1  per  cent,  solution  of  sodium  carbonate,  mix  well, 
and  keep  at  the  stated  temperature.  At  the  expiration  of  one  minute  take  out 
a  drop  of  the  mixture,  place  it  on  a  white  plate,  and  add  a  drop  of  dilute 
iodine  solution.  The  mixture  will  turn  blue.  Eepeat  testing  the  mixture, 
which  is  to  be  kept  at  the  same  temperature,  every  minute  until  iodine  has  no 
longer  any  effect  on  the  solution,  indicating  the  conversion  of  all  starch  into 
simple  sugars.  With  normal  saliva  the  color  reaction  will  cease  within  six 
minutes ;  a  longer  time  would  indicate  an  insufficient  quantity  of  ptyalin  in 
the  saliva  used  for  the  experiment. 

When  the  solution  no  longer  is  affected  by  iodine  add  to  1  c.c.  of  solution  6 
c.c.  of  alcohol :  a  precipitate  of  dextrin  is  formed.  Allow  the  digestion  to 
proceed  for  half  an  hour,  then  heat  some  of  the  digested  mixture  with  Feh- 
ling's  solution:  the  formation  of  red  cuprous  oxide  shows  the  conversion  of 
starch  into  glucose. 

Action  of  adds  and  alkalies  on  salivary  digestion.  In  each  of  three  test-tubes, 
A,  B,  and  C,  place  5  c.c.  of  starch  paste,  prepared  as  above,  and  1  c.c.  of  saliva. 
To  A  add  3  c.c.  of  0.25  per  cent,  hydrochloric  acid ;  to  B  add  3  c.c.  of  1  per 
cent,  sodium  carbonate.  Keep  the  tubes  at  40°  C.,  and  note  the  time  required 
for  the  disappearance  of  the  iodine  color  reaction  with  the  contents  of  each 
tube.  The  reaction  will  disappear  first  in  B,  then  in  C,  and  finally  in  A. 

In  order  to  obtain  saliva  for  experimental  purposes  a  small  glass 
rod  or  a  piece  of  rubber  should  be  placed  in  the  mouth.  This  will 
stimulate  the  flow  of  saliva,  which  is  to  be  collected  and  filtered. 

43 


674  PHYSIOLOGICAL   CHEMISTRY. 

General  tests  for  mixed  saliva. 

1.  Allow  a  few  c.c.  of  saliva  to  stand  a  day  or  two  :  a  cloudiness 
will  be  observed,  due  to  the  precipitation  of  calcium  carbonate,  which 
has  been  held  in  solution  by  carbon  dioxide. 

2.  Acidify  saliva  with  acetic  acid  :  a  precipitate  of  mucin  is  formed 
insoluble  in  an  excess  of  the  acid. 

3.  Apply  the   xanthoproteic,  Millon's,   and   biuret   reactions  for 
proteins  (see  page  626). 

4.  Acidify  with  acetic  acid  and  add  ferric  chloride  :  a  red  color, 
due  to  the  formation  of  ferric  sulphocyanide,  is  produced. 

Gastric  digestion.  The  food,  after  mastication,  passes  through 
the  oesophagus  into  the  stomach.  Here  the  mass  is  kneaded  by  the 
contractions  of  the  muscular  wall  of  the  stomach  and  is  acted  on  by 
the  gastric  juice.  By  this  treatment  with  the  aid  of  the  fluids 
ingested  the  food  is  converted  into  a  turbid  liquid,  known  as  chyme. 
A  small  portion  of  the  digested  mass  is  absorbed  through  the  stomach 
wall,  but  most  of  the  food,  after  being  completely  acted  upon,  passes 
through  the  pylorus  into  the  duodenum. 

Gastric  juice  is  a  liquid  secreted  by  the  follicles  of  the  stomach. 
It  can  be  obtained,  in  a  fairly  normal  condition,  either  from  animals 
(dogs)  or  from  man,  by  the  aid  either  of  gastric  fistulse  or  of  the 
stomach-pump.  It  is  a  thin,  nearly  colorless  liquid,  having  a  some- 
what sour  taste,  an  acid  reaction,  and  a  specific  gravity  varying  from 
1.002  to  1.003.  The  total  solids  are  about  0.5  per  cent.,  nearly  one- 
half  being  inorganic  salts,  chiefly  the  chlorides  and  phosphates 
of  alkali  and  alkaline  earth  metals.  The  organic  matter  present, 
and  amounting  to  about  0.3  per  cent.,  is  chiefly  pepsin  and  a  little 
mucin. 

The  secretion  of  gastric  juice  is  not  continuous,  and  is  brought 
about  by  chemical  irritation  of  the  gastric  mucuous  membrane  or  by 
psychic  influence.  A  strong  desire  for  food  will  cause  a  flow  of  the 
juice  ;  chemical  irritation,  as  by  the  alkaline  mass  of  food  and  saliva, 
causes  a  slower  but  more  continuous  flow.  The  quantity  of  juice 
secreted  during  digestion  varies  with  the  quantity  and  quality  of  the 
food. 

The  average  composition  of  pure  gastric  juice  may  be  approxi- 
mately stated  thus : 

Water 99. 26  per  cent. 

Pepsin  and  other  organic  matter    .         .         .         .0.30 
Rennin  .  y 

Free  hydrochloric  acid  ....  0.22 

Alkali  chlorides 0  20 

Phosphates  of  calcium,  magnesium,  and  iron          .       0.02 


DIGESTION.  675 

The  acidity  of  gastric  juice  is  due  chiefly  to  hydrochloric  acid, 
present  in  quantities  varying  from  0.1  to  0.3,  or  even  0.4  per  cent.; 
to  a  slight  extent  also  to  organic  acids  and  acid  salts.  The  presence 
of  free  acid  in  gastric  juice  cannot  be  demonstrated  until  about 
twenty  minutes  after  the  swallowing  of  food ;  this  is  due  to  the 
power  of  proteins  to  form  compounds  with  hydrochloric  acid.  During 
this  time  the  ptyalin  of  saliva  is  active  in  the  hydrolysis  of  starch. 
The  gastric  juice  is  the  only  secretion  of  the  body  containing  free 
acid.  The  mode  of  production  of  the  hydrochloric  acid  is  not  under- 
stood. While  it  is  known  that  it  is  derived  from  the  chlorides  of  the 
blood,  the  details  of  the  process  are  not  yet  worked  out.  The  function 
of  the  acid  is  to  activate  the  enzymes  of  the  stomach  which  are  se- 
creted in  the  zymogen  state,  and  to  aid  in  peptic  digestion.  It  also 
has  a  marked  antiseptic  action  upon  the  contents  of  the  stomach  and 
upper  intestine.  Organic  acids,  chiefly  lactic,  are  frequently  found  in 
the  stomach,  but  these  are  not  secreted  in  the  gastric  juice  itself,  but 
are  produced  by  some  fermentative  action  from  the  food  after  it  has 
entered  the  stomach.  Lactic  acid  is  never  found  in  a  normal  stomach 
unless  it  was  present  in  the  food  before  ingestion.  It  is  often  present 
in  cases  of  gastric  stagnation  with  a  decreased  hydrochloric  output. 
These  cases  may  be  either  benign  or,  more  often,  malignant  in  origin. 
Thus,  the  persistent  occurrence  of  lactic  acid  with  a  diminution  or 
absence  of  hydrochloric  acid  is  an  indication  of  serious  disturbances, 
possibly  of  cancer  of  the  stomach. 

The  origin  of  the  lactic  acid  is  the  carbohydrate  food ;  other  food 
material  may  of  course  produce  other  organic  acids  (e.  g.,  butyric  acid 
from  butter). 

The  enzymes  of  gastric  juice.  The  two  important  enzymes  of  the 
stomach  are  pepsin  and  rennin,  which  are  secreted  in  an  inactive  or 
zymogen  form,  and  are  activated  by  the  hydrochloric  acid  of  the  gas- 
tric juice.  In  addition  to  these  there  is  probably  a  lipolytic  enzyme 
(gastric  lipase)  present.  In  the  cardiac  end  of  the  stomach  the  reaction 
does  not  become  acid  for  some  time  after  digestion  commences,  and  the 
ptyalin  of  the  saliva  continues  its  action  on  the  starches  during  this  time. 

Digestive  action  of  gastric  juice.  The  conversion  of  proteins  into 
peptone  is  a  progressive  reaction  due  to  the  action  of  pepsin  in  hydro- 
chloric acid  solution.  Simple  proteins  are  first  changed  into  syn- 
tonin,  an  acid  albuminate  ;  this  is  split  into  compounds  known  as 
primary  proteoses  (proto-proteoses,  protalbumoses).  By  further  action 
these  primary  proteoses  form  secondary  proteoses  (deutero-proteoses, 
deutero-albumoses),  which  are  finally  split,  forming  peptones. 


676  PHYSIOLOGICAL   CHEMISTRY. 

Peptone  is  the  end-product  of  gastric  digestion,  is  diffusible,  and 
is  not  further  changed  by  pepsin.  The  intermediate  products  exist 
at  the  same  time  in  gastric  digestion,  their  relative  quantities  depend- 
ing on  tiie  length  of  time  the  action  has  progressed. 

While  it  is  believed  that  gastric  digestion  normally  carries  the  de- 
composition of  proteins  no  further  than  this,  it  is  possible  to  split 
proteins  into  the  amino-bodies  by  pepsin-hydrochloric  acid  digestion 
outside  of  the  body. 

Compound  proteins  are  split  by  gastric  juice,  the  simple  proteins 
formed  being  digested  as  above  stated.  The  nucleoproteins  yield  a 
peptone  free  from  phosphorus,  the  nuclein  split  off  being  unchanged. 
Collagen  is  first  converted  into  gelatin,  which  then  forms  successively 
an  acid  albumin,  proto-proteose,  deutero-proteose,  and  gelatin-peptone. 
Elastin  is  changed  slowly,  while  keratins  are  not  changed  at  all. 

Rennin  is  a  milk-curdling  enzyme  present  in  all  normal  human 
gastric  juice.  It  is  absent  in  chronic  catarrh  of  the  stomach  and 
other  diseases.  Its  presence  in  gastric  juice  is  shown  by  its  action 
on  milk,  and  will  be  considered  in  the  article  on  clinical  examination 
of  gastric  juice. 

Absorption  in  the  stomach.  It  has  been  shown  that  the  stomach  is 
able  to  absorb  sugars,  peptones,  salts,  and  some  drugs.  However, 
the  absorption  is  not  extensive  unless  concentrated  solutions  are 
present,  and  probably  plays  no  great  part  in  normal  metabolism. 

Experiment  80.  (Artificial  gastric  digestion.)  Dissolve  2  grammes  of  scale 
pepsin  in  1000  c.c.  of  0.4  per  cent,  hydrochloric  acid.  To  this  solution  add 
about  250  grammes  of  protein.  The  protein  material  may  be  fresh  or  dried 
blood-fibrin,  the  meat- residue  from  the  preparation  of  creatine  (Experiment  77), 
or  the  whites  of  18  eggs,  previously  boiled  and  finely  divided.  The  fresh  fibrin 
or  the  egg-albumin  may  be  added  directly  to  the  digestive  fluid.  The  meat- 
residue  or  dried  fibrin  should  first  be  boiled  with  a  liter  of  water,  containing 
1  c.c.  of  hydrochloric  acid,  until  the  material  gelatinizes ;  it  must  be  cooled 
before  mixing  it  with  the  digestive  fluid.  Keep  mixture  in  a  thermostat  at  a 
temperature  of  40°  C.  (104°  F.)  for  ten  days.  Filter  the  solution,  heat  the 
filtrate  to  50°  C.  (122°  F.),  and  neutralize  with  sodium  carbonate,  when  syntonin 
is  precipitated. 

Evaporate  filtrate  from  syntonin  to  about  200  c.c.,  adding  sodium  carbonate 
if  necessary  to  keep  solution  neutral  during  evaporation,  filter,  and  saturate 
solution  with  ammonium  sulphate,  when  protease  is  precipitated,  while  peptone 
remains  in  solution. 

To  purify  the  proteose,  dissolve  the  precipitate  in  water,  heat  to  boiling,  and 
add  barium  carbonate  until  all  ammonium  sulphate  is  decomposed.  Filter, 
evaporate  filtrate  to  a  small  volume,  and  pour  solution  into  double  the  volume 
of  95  per  cent,  alcohol,  when  proteose  is  precipitated  as  a  sticky  mass.  To 
obtain  it  as  a  powder,  allow  the  mass  to  remain  in  contact  with  the  alcohol  for 


DIGESTION.  677 

two  hours,  transfer  to  absolute  alcohol  for  one  hour,  and  then  to  ether  for  an 
hour;  then  collect  on  a  filter  and  dry  between  filter-paper.  The  proteose  thus 
obtained  is  a  mixture  of  primary  and  secondary  proteoses. 

Use  an  aqueous  solution  of  this  proteose  for  the  following  tests :  Acidulate 
a  portion  with  acetic  acid  and  add  an  equal  volume  of  saturated  solution  of 
sodium  chloride.  The  solution  becomes  cloudy,  clearing  again  when  heat  is 
applied,  and  becoming  cloudy  again  when  cool.  (Characteristic  of  proteoses.) 
Other  portions  of  the  solution  use  for  the  xanthoproteic,  Millon's,  and  biuret 
reactions. 

Proteoses  will  give  positive  precipitation  tests  with  acetic  acid  and  ferro- 
cyanide,  and  with  trichloracetic  acid.  Peptones  will  give  negative  results  with 
the  same  tests. 

To  obtain  peptone,  the  filtrate  from  the  proteose  is  heated  and  20  grammes 
of  ammonium  sulphate  are  added  to  remove  traces  of  proteose.  The  filtrate, 
after  being  concentrated  by  evaporation,  is  treated  with  barium  carbonate, 
alcohol  and  ether,  exactly  as  directed  above  for  proteose.  Use  some  of  the 
peptones  for  the  xanthoproteic,  Millon's,  and  biuret  reactions. 

Clinical  examination  of  gastric  juice.  The  chemical  examina- 
tion of  gastric  juice,  or  of  contents  of  stomach,  is  now  considered  of 
great  importance  in  the  diagnosis  of  diseases  of  the  stomach.  The 
juice  for  examination  is  obtained  as  follows  :  On  an  empty  stomach, 
the  patient  partakes  of  a  test-meal,  consisting  usually  of  bread  and 
water,  and  an  hour  after  or  later  (depending  upon  the  form  of  meal 
administered)  the  contents  of  the  meal  are  withdrawn  by  means  of  a 
stomach-tube.  The  liquid  is  filtered  and  used  for  further  examina- 
tions. These  examinations  consist  of  the  following  determinations  : 
a.  reaction ;  b.  presence  of  free  acids ;  c.  presence  of  free  hydro- 
chloric acid ;  d.  presence  of  lactic  and  other  organic  acids ;  e.  total 
acidity  ;  /.  estimation  of  free  acids  ;  g.  estimation  of  free  hydrochloric 
acid ;  h.  estimation  of  combined  hydrochloric  acid ;  i.  estimation  of 
total  organic  acids  ;  j.  presence  of  pepsin  and  pepsinogen  ;  k.  presence 
of  renuin  and  rennin  zymogen  ;  I,  detection  of  proteins ;  m,  detection 
of  carbohydrates. 

In  case  a  sufficient  supply  of  gastric  juice  cannot  be  obtained  for  the  reac- 
tions below,  the  student  should  prepare  the  following  solutions  :  A.  A  0.25  per 
cent,  hydrochloric  acid  ;  B.  A  mixture  of  10  parts  of  A  and  40  parts  of  water; 
C.  A  solution  of  0.8  gramme  of  lactic  acid  in  100  c.c.  of  water ;  D.  A  2  per 
cent,  solution  of  albumose  in  water.  Make  reactions  b  and  c  with  solution  A, 
repeat  with  B,  and  with  a  mixture  of  1  part  of  B  and  2  parts  of  D. 

a.  Reaction.  This  should  be,  and  in  all  normal  juices  is,  distinctly 
acid  to  litmus-paper. 

6.  Free  acids.  The  presence  of  free  acids  is  detected  by  congo-red 
paper.  This  paper  is  prepared  by  soaking  unsized  paper  in  a  1  per 
cent,  aqueous  solution  of  congo-red,  and  drying.  If  a  drop  of  juice 


678  PHYSIOLOGICAL   CHEMISTRY. 

is  placed  upon  the  paper,  the  presence  of  free  acids  is  indicated  by 
the  change  of  color  from  red  to  blue ;  if  the  blue  color  is  intense, 
free  hydrochloric  acid  is  present.  (Neither  combined  hydrochloric 
acid  nor  acid  salts,  such  as  acid  phosphates,  act  on  congo-red.) 

c.  Free  hydrochloric  acid.     There  are  a  number  of  reagents  for  the 
detection  of  free  hydrochloric  acid.     The  more  important  of  these 
are :    tropaeolin    00,   phloroglucin-vanillin,   resorcin,    and    dimethyl- 
amino-azobenzol. 

Tropceolin  00.  Dissolved  in  water,  the  1  per  cent,  brownish -yel- 
low solution  of  tropaeolin  00  (diphenylamine-orange)  is  changed  to  a 
brown-red  or  deep-red  color  upon  the  addition  of  juice  containing 
free  hydrochloric  acid.  Upon  gentle  evaporation  and  heating  a  lilac 
color  is  produced.  The  same  reaction  may  be  made  with  filter-paper, 
soaked  for  some  time  in  an  alcoholic  solution  of  the  reagent,  allowed 
to  dry,  and  used  as  test-paper.  Hydrochloric  acid  turns  this  paper 
brown,  and  upon  heating  the  brown  color  changes  to  blue.  (The 
paper  does  not  keep  unchanged  over  a  month.) 

Phloroglucin-vanillin.  This  reagent  is  made  by  dissolving  2  parts 
of  phloroglucin  and  1  part  of  vanillin  in  30  parts  of  alcohol.  It  is 
a  very  sensitive  and  reliable  agent  for  the  detection  of  free  hydro- 
chloric acid.  ^Five  drops  of  the  solution  mixed  with  an  equal  quan- 
tity of  gastric  filtrate  are  gently  heated  over  a  Bunsen  flame.  On 
complete  evaporation  a  distinct  red  color  or  tinge  appears  in  the 
presence  of  not  less  than  0.01  per  cent,  of  hydrochloric  acid.  The 
formation  of  cherry-red  crystals  indicates  the  presence  of  large  quan- 
tities of  the  acid.  Organic  acids  have  no  action  on  this  reagent. 

Resorcin.  This  reagent  is  equally  as  sensitive  as,  and  more  stable 
than,  phloroglucin-vanillin.  The  solution  is  obtained  by  dissolving 
5  parts  of  resublimed  resorcin  and  3  parts  of  cane-sugar  in  100  parts 
of  dilute  alcohol.  The  manner  of  testing  with  this  reagent  is  the 
same  as  described  above  for  phloroglucin-vanillin  ;  a  bright-red  tinge 
or  color  appears,  even  when  very  small  quantities  of  free  hydrochloric 
acid  are  present. 

Dimeihyl-amido-azobeMzol.  A  0.5  per  cent,  solution  of  this  substance 
in  alcohol  is  mixed  with  a  few  drops  of  the  stomach  contents,  and  in 
the  presence  of  as  little  as  0.002  percent,  of  free  hydrochloric  acid  a 
cherry-red  color  develops. 

d.  Lactic  acid.     (Use  solution  C.)     Uffelmann's  reagent  answers 
best  for  detecting  this  acid.     It  is  made  by  adding  1  or  2  drops  of 
ferric  chloride  solution  to  10  c.c.  of  a  1  per  cent,  carbolic  acid  solu- 
tion, and   diluting   this   solution   with    water  until  it  assumes  an 


DIGESTION.  679 

amethyst-blue  color.  To  2  c.c.  of  this  solution  an  equal  volume  of 
gastric  juice  is  added.  In  the  presence  of  at  least  0.01  per  cent,  of 
lactic  acid  the  liquid  assumes  a  pure  yellow  color.  As  the  presence 
of  too  much  hydrochloric  acid  (or  even  of  some  other  substances) 
prevents  the  change,  it  is  well  to  shake  (in  doubtful  cases)  10  c.c. 
of  juice  with  50  c.c.  of  ether,  evaporating  the  ethereal  solution 
to  dryness,  dissolving  the  residue  in  a  few  drops  of  water,  and 
adding  to  this  solution,  which  contains  the  lactic  acid,  the  above 
reagent. 

Butyric  acid  changes  Uffelmann's  reagent  to  brownish  yellow. 
Butyric  and  acetic  acids  may  be  recognized  by  their  odor. 

It  has  been  mentioned  that  the  total  acidity  of  gastric  juice  is  due  to  acid 
salts,  organic  acids,  free  and  combined  hydrochloric  acid.  Clinically  it  is 
sometimes  necessary  to  estimate  the  acidity  due  to  each.  This  is  done  by  the 
following  method. 

e.  Total  acidity.  This  is  best  determined  by  titration  with  an 
alkali ;  the  estimation  is  conducted  as  follows :  To  10  c.c.  of  the 
filtered  liquid  a  few  drops  of  phenolphthalein  solution  are  added,  and 
to  the  mixture  deci-normal  potassium  hydroxide  solution  is  slowly 
added  from  a  burette  until  the  liquid  assumes  a  slight  reddish  tint, 
which  does  not  disappear  on  stirring. 

It  is  customary  to  express  the  acidity  in  percentages,  according  to 
the  quantity  of  deci-normal  potassium  hydroxide  used.  Thus,  52 
per  cent,  acidity  would  indicate  that  every  100  c.c.  of  gastric  fil- 
trate are  exactly  neutralized  by  52  c.c.  of  deci-normal  potassium 
hydroxide. 

Though  the  total  acidity  is  due  to  a  mixture  of  free  and  combined 
hydrochloric  acid,  organic  acids,  and  acid  salts,  it  is  frequently 
expressed  as  hydrochloric  acid.  As  1  c.c.  of  deci-normal  alkali 
solution  corresponds  to  0.003618  gramme  of  HC1,  the  number  of 
c.c.  of  alkali  used  multiplied  by  the  factor  stated,  gives  the  grammes 
of  HC1  in  the  10  c.c.  of  juice  used.  Suppose  5.2  c.c.  of  alkali  were 
required;  this  would  correspond  to  5.2  X  0.003618,  equal  to  0.0188 
gramme  of  HC1  in  10  c.c.,  or  to  0.188  per  cent. 

/.  Estimation  of  free  acids.  Both  free  hydrochloric  and  organic 
acids  change  the  bright-red  color  of  congo-red  to  blue,  while  alkalies 
restore  it  to  red.  Acid  salts,  such  as  acid  phosphates,  have  no  effect 
on  this  indicator.  If,  therefore,  a  titration  of  10  c.c.  of  filtered  gas- 
tric juice,  to  which  enough  of  congo-red  solution  has  been  added  to 
impart  a  distinct  blue  color,  is  made  (as  above  described  for  total 
acidity),  then  the  number  of  c.c.  of  deci-normal  potassium  hydroxide 


680  PHYSIOLOGICAL  CHEMISTRY. 

solution  used  to  restore  the  red  color  indicates  the  quantity  of  free 
acid  present.  The  calculation  is  made  as  above  mentioned. 

g.  Estimation  of  free  hydrochloric  acid.  The  use  of  dimethyl- 
ami  no-azobenzol  as  an  indicator  for  free  hydrochloric  acid  has  been 
mentioned  above.  For  quantitative  work  10  c.c.  of  gastric  filtrate 
are  mixed  with  5  drops  of  the  dimethyl-amino-azobenzol  solution, 
and  this  mixture  is  titrated  with  ^  sodium  hydroxide  solution.  The 
disappearance  of  the  reddish  color  indicates  when  the  reaction  is 
completed.  The  difference  between  the  estimation  of  total  free  acids 
(/)  and  that  of  free  hydrochloric  acid  (g)  indicates  the  quantity  of 
organic  acids  present. 

h.  Estimation  of  combined  hydrochloric  acid.  To  10  c.c.  of  gas- 
tric juice  add  3  drops  of  a  1  per  cent,  alizarin  solution  and  titrate 
with  YQ  alkali  until  the  solution  assumes  a  clear  violet  color.  The 
acidity  thus  determined  is  due  to  free  hydrochloric  acid,  acid  salts, 
and  organic  acids.  The  difference  between  the  results  of  titration 
with  alizarin  (A)  and  with  phenol-phthalein  (e)  shows  acidity  due  to 
combined  hydrochloric  acid,  while  the  difference  between  the  titra- 
tion with  alizarin  (h)  and  that  with  dimethyl-amino-azobenzol  shows 
acidity  due  to  organic  acids  and  acid  salts. 

i.  The  total  organic  acids,  free  and  combined,  may  be  determined 
by  neutralizing  10  c.c.  of  gastric  juice,  using  phenolphthalein  as  an 
indicator,  evaporating  the  neutral  solution  to  dryness  and  incinerating 
the  residue.  By  this  operation  the  organic  acids  are  converted  into 
carbonates,  which  are  titrated  with  ^  acid,  and  from  the  result  the 
quantity  of  organic  acid  is  calculated,  usually  as  lactic  acid. 

j.  Pepsin  and  pepsinogen.  In  case  free  acid  is  present,  10  c.c.  of 
gastric  juice  are  placed  in  a  beaker,  and  a  small  bit  of  dried  fibrin 
or  a  lamella  of  blood  albumin  (Merck),  is  added,  and  the  beaker 
placed  in  a  thermostat  at  a  constant  temperature  of  38°  to  40°  C. 
(100°  to  104°  F.).  Pepsin  is  indicated  by  the  rapid  solution  of  the 
flake  of  albumin.  If  free  hydrochloric  acid  is  absent,  the  juice  is 
rendered  acid  with  a  drop  of  this  acid  and  then  tested  in  the  manner 
described. 

k.  Rennin  enzyme  and  rennin  zymogen.  Rennin  is  tested  for  as 
follows :  10  c.c.  of  gastric  juice  are  exactly  neutralized  with  deci- 
normal  alkali  and  mixed  with  an  equal  volume  of  neutral  unboiled 
milk.  The  mixture  is  placed  in  a  thermostat  at  38°  C.  (100°  F.). 
If  a  casein  coagulum  is  formed  in  ten  to  fifteen  minutes,  the  coagula- 
tion is  due  to  the  rennin  enzyme. 

Rennin  zymogen  is  detected  thus:    10  c.c.  of  gastric  juice   are 


PLATE  VII 

INDICATORS  FOR  ALKALIES  AND  ACIDS. 


Litmus. 


Congo  red. 


3 


Phenolphthalein. 


flethy  1- orange  ;     Dimethj  I-amido- 
azobenzol ;    Tropseolin    D. 


5 


Alizarin  for  acids. 

I  ffelmann's  test  for  lactic  acid. 


Gunzburg's  phloroglucin- vanillin 
test  or  Boas'  resorcin  test  for  free  hy- 
drochloric acid. 


Methyl-violet. 


Haematoxylin. 


A  ffocn  &  Co  Lie/i.  Baltimore.,  .Wd. 

The  colors  on  the  left  indicate  alkaline,  those  on   the  right  acid   reaction. 
For  explanation  see  page  in  Index. 


DIGESTION.  681 

rendered  feebly  alkaline  and  mixed  with  2  c.o.  of  a  1  per  cent, 
solution  of  calcium  chloride  and  10  c.c.  of  milk.  If  the  rennin 
zymogen  be  present,  a  heavy  cake  of  casein  is  precipitated  in  a  few 
minutes. 

1.  'Detection  of  proteins.  Of  these,  syntonin,  albumoses,  and  pep- 
tones are  to  be  looked  for.  Syntonin :  The  gastric  filtrate  is  exactly 
neutralized,  whereupon  a  cloudiness  or  precipitate  is  formed,  which 
is  soluble  both  in  alkalies  and  in  acids.  Albumoses:  These  are  pre- 
cipitated by  a  saturated  solution  of  ammonium  sulphate,  while  pep- 
tones remain  in  solution.  Peptones :  These  are  recognized  by  the 
biuret-test.  The  juice  is  rendered  strongly  alkaline  with  potassium 
hydroxide  and  a  few  drops  of  a  cupric  sulphate  solution  (1  in  1000) 
are  added.  A  red  color  indicates  the  presence  of  peptones. 

ra.  Detection  of  carbohydrates.  Starch  is  recognized  by  the  blue 
color  produced  by  iodine  solution  (1  iodine,  2  potassium  iodide,  100 
water).  The  reaction  is  less  marked  in  proportion  to  the  amount  of 
starch  converted  into  dextrin  and  sugar. 

Erythrodextrin  gives  a  mahogany-brown  color,  and  achroodextrin 
remains  unchanged  by  the  iodine  solution.  Inasmuch  as  sugar  is 
present  in  the  test-meal  itself,  it  is  useless  to  test  for  this  substance. 

Intestinal  digestion.  The  changes  in  food  taking  place  in  the 
small  intestine  are  much  more  complex  and  far-reaching  than  those 
occurring  in  the  stomach.  Little  or  no  absorption  takes  place  from 
the  stomach,  and  the  alterations  in  the  food  brought  about  by  the 
gastric  juice  can  be  considered  as  being  largely  preparatory  for  the 
action  of  the  digestive  fluids  of  the  intestine.  The  close  dependence 
of  one  part  of  the  process  of  digestion  on  the  other  is  shown  by  the 
normal  effect  of  the  entrance  of  chyme  into  the  duodenum.  The 
acid  chyme  causes  a  reflex  secretion  of  the  pancreatic  juice,  the  bile, 
and  the  intestinal  juice,  the  digestive  fluids  of  the  intestine.  These 
fluids  are  all  alkaline,  and  are  secreted  in  sufficient  quantity  to  neu- 
tralize the  chyme  and  to  provide  the  degree  of  alkalinity  most  suit- 
able for  the  action  of  the  ferments  which  complete  the  process  of 
digestion.  A  slight  increase  of  the  acidity  of  the  gastric  contents  is 
followed  by  an  increase  in  the  secretion  of  the  digestive  fluids  of  the 
intestine.  Intestinal  digestion  depends  upon  three  secretions :  (1) 
the  pancreatic  juice ;  (2)  the  bile ;  (3)  the  succus  entericus,  the  secre- 
tion of  the  intestine. 

Pancreatic  secretions.  The  secretions  of  the  pancreas  are  of 
two  kinds,  an  external,  the  pancreatic  juice,  which  flows  into  the 


682  PHYSIOLOGICAL  CHEMISTRY. 

intestine,  and  an  internal  secretion,  which  passes  directly  into  the 
blood,  and  has  a  governing  power  over  the  metabolism  of  sugar  and 
the  conversion  of  glycogeu  into  sugar  by  the  liver. 

Pancreatic  juice.  There  is  no  thoroughly  reliable  analysis  of  this 
highly  complex  liquid  on  record.  It  is  an  alkaline  liquid  containing 
from  3  to  6  per  cent,  of  solids,  two-thirds  of  which  are  of  organic, 
one-third  of  inorganic  nature.  Among  the  organic  constituents  are 
a  number  (certainly  three,  probably  four)  of  enzymes  :  1.  Amylopsin 
converts  starch  into  sugar  (this  action  is  more  energetic  than  that  of 
ptyalin) ;  2.  Trypsin  converts  proteins  into  peptones  (this  action  takes 
place  in  alkaline,  but  not  in  acid  solution,  as  in  case  of  pepsin) ;  3. 
Steapsin  decomposes  fats  into  glycerin  and  fatty  acids ;  4.  A  milk- 
curdling  enzyme.  The  inorganic  solids  are  chiefly  alkali  chlorides 
and  carbonates,  with  some  calcium,  magnesium,  and  iron  phosphates. 

The  quality  of  the  food  has  an  unmistakable  influence  on  the  com- 
position of  the  juice  and  on  the  quantity  of  the  different  enzymes. 
Thus,  the  juice  is  always  richest  in  diastatic  enzyme  after  a  bread 
diet,  and  richest  in  steapsin  after  a  meal  consisting  of  much  fat. 

The  secretion  of  pancreatic  juice  is  thought  to  be  caused  by  stimuli 
reaching  the  pancreas  by  two  routes  :  (1)  nervous  stimuli  by  the  sym- 
pathetic nerves;  (2)  chemical  stimuli  by  the  blood-stream.  The 
chemical  substance  concerned  is  termed  secretin,  and  is  formed  in  the 
intestine  as  soon  as  hydrochloric  acid  is  admitted  from  the  stomach 
during  the  course  of  digestion.  The  HC1  acts  upon  a  substance 
normally  present  (prosecretin),  transforming  it  to  secretin,  which  is 
absorbed  and  carried  by  the  blood  to  the  pancreas.  Secretin  belongs 
to  the  class  of  bodies  called  hormones. 

The  trypsin  of  the  pancreatic  juice  is  for  the  most  part  secreted  in 
an  inactive  or  zymogen  state  (trypsinogen),  and  becomes  active  when 
it  meets  the  kinase  of  the  intestine  (enterokinase).  The  other  enzymes 
(amylopsin,  steapsin)  are  secreted  mainly  in  the  active  condition. 

Amylopsin  (diastase)  is  closely  related  to  ptyalin,  and  converts  raw 
or  boiled  starch  into  erythrodextrin,  achrobdextrin,  and  finally  into 
maltose  and  dextrose.  The  dextrose  is  probably  formed  by  the  in- 
vertin  of  the  intestinal  juice. 

Experiment  81.  (Diastatic  action  of  pancreatin.)  Dissolve  1  gramme  of  pan- 
creatin  in  500  c.c.  of  water,  and  after  standing  at  40°  C.  (104°  F.)  for  two  hours 
filter  the  solution.  Mix  in  a  test-tube  equal  volumes  of  the  solution  and  starch 
paste,  prepared  as  directed  in  Experiment  79,  and  heat  at  40°  C.  (104°  F.). 
Notice  that  the  material  gradually*  becomes  transparent,  reduces  Fehling's 
solution,  and  is  not  colored  blue  by  iodine  solution.  Repeat  the  experiment 
with  a  boiled  solution  of  pancreatin,  and  notice  that  it  has  no  effect  on  starch, 


DIGESFION.  683 

the  enzyme  having  been  destroyed  by  heat.  (The  pancreatin  solution  itself 
should  be  tested  with  Fehling's  solution,  as  the  commercial  article  is  frequently 
adulterated  with  sugar.) 

Steapsin  (lipase)  splits  the  neutral  fats  into  fatty  acids  and  glycerin. 
The  liberated  fatty  acids  combine  with  alkali  of  the  pancreatic  juice, 
forming  soap.  The  action  of  lipase  is  materially  aided  by  the  pres- 
ence of  bile,  although  it  is  not  understood  how  this  occurs. 

Experiment  82.  (Fat-splitting  action  of  steapsin.}  (Fresh  pancreas  must  be 
used  for  the  experiment.)  Shake  about  2  grammes  of  butter  with  a  few  c.c.  of 
lukewarm  water,  to  which  a  drop  of  caustic  soda  solution  has  been  added. 
After  cooling  shake  with  an  equal  volume  of  ether,  pour  the  ethereal  solution 
on  a  watch-glass  and  allow  the  ether  to  evaporate.  To  the  neutral  butter  fat 
thus  obtained  add  a  piece  of  fresh  pancreas  the  size  of  a  pea,  mix  the  materials 
intimately  by  rubbing,  and  place  in  a  thermostat  at  40°  C.  (104°  F.).  After  a 
few  minutes  the  odor  of  butyric  acid  will  be  recognized. 

Shake  a  gramme  of  butter  fat,  obtained  as  above,  with  about  5  c.c.  of  luke- 
warm water,  render  slightly  alkaline  with  sodium  carbonate,  using  rosolic  acid 
as  an  indicator,  add  some  fresh  pancreas  converted  into  a  thin  paste  by  grind- 
ing with  water,  and  keep  the  mixture  at  40°  C.  (104°  F.)  for  twelve  hours. 
Notice  that  the  mixture  turns  yellow,  due  to  the  acid  liberated  from  the  butter 
fat.  The  experiment  when  made  with  boiled  pancreas  does  not  show  liberation 
of  acid. 

Trypxin  breaks  down  proteins  by  a  series  of  changes  almost  iden- 
tical with  those  produced  by  pepsin.  It  is,  however,  most  active  in 
an  alkaline  medium,  and  has  a  more  rapid  and  complete  action  than 
that  of  pepsin.  The  digestions  by  pepsin  and  trypsin  are  to  a  certain  ex- 
tent supplementary  to  each  other,  for  it  is  found  that  proteins  subjected 
to  both  are  more  thoroughly  decomposed  than  by  either  one  alone. 
Under  normal  conditions  it  is  probable  that  tryptic  digestion  produces 
a  considerable  amount  of  amino-bodies,  and  that  the  remainder  of  the 
peptones  and  proteoses  are  split  up  by  the  intestinal  enzyme,  erepsin. 

Experiment  83.  (Artificial  tryptic  digestion.}  To  250  grammes  of  protein  add 
a  solution  of  5  grammes  of  sodium  carbonate,  3  grammes  of  pancreatin,  and 
5  c.c.  of  chloroform.  Keep  in  a  thermostat  at  40°  C.  (104°  F.)  for  ten  days. 
Then  filter  off  a  few  c.c.  of  the  liquid  and  add  bromine-water.  A  violet  color 
is  produced,  due  to  tryptophane.  Acidify  the  digested  mixture  with  acetic 
acid,  boil,  filter,  evaporate  filtrate  to  150  c.c.,  and  allow  to  stand  in  a  cool 
place.  In  a  few  hours  crystals  of  tyrosine  will  be  deposited.  Decant  the 
mother-liquor  and  purify  the  tyrosine  by  recrystallizing  from  a  solution  con- 
taining a  little  ammonia.  Use  the  crystals  to  test  for  tyrosine  (see  Index). 

Evaporate  the  mother-liquor  from  the  tyrosine  to  a  thin  syrup,  add  200  c.c. 
of  hot  alcohol,  allow  the  mixture  to  cool,  and  filter.  Evaporate  the  filtrate  to 
dryness,  dissolve  the  residue  in  water,  and  boil  with  freshly  prepared  lead 
hydroxide.  Allow  to  cool,  filter,  free  the  filtrate  from  lead  by  means  of 


684  PHYSIOLOGICAL  CHEMISTRY. 

hydrogen  sulphide,  and  evaporate  to  a  small  volume.  The  leucine  which  is 
precipitated  on  standing  is  best  separated  from  the  mother-liquor  by  placing 
the  mass  on  a  plate  of  porous  clay.  Use  the  crystals  to  make  reactions  for 
leucine  (see  Index). 

Bile,  secreted  by  the  liver,  is  a  thin,  transparent  liquid  of  a  golden- 
yellow  color,  and  a  specific  gravity  of  1.020  ;  it  has  a  very  bitter  taste 
and  an  alkaline  reaction  ;  it  varies  widely  in  composition,  the  total 
solids  ranging  from  9  to  17  per  cent.,  being  always  highest  after  a 
meal  ;  its  composition,  moreover,  is  highly  complex ;  the  following  is 
an  average  of  five  analyses  of  bile  from  subjects  with  healthy  livers  : 

Water 91.68  per  cent. 

Mucus  and  pigment 1.29  " 

Taurocholate  of  sodium 0.87 

Glycocholate  of  sodium  § 3.03  " 

Fat         .                                  0.73 

Soaps  •   .        . 1.39  " 

Cholesterin 0.35  " 

Lecithin 0.53  « 

Bile  obtained  after  death  is  of  a  brownish-yellow  color ;  freed  from 
mucus  it  will  remain  undecomposed  for  an  almost  indefinite  period. 
The  mucus  may  be  separated  by  the  addition  of  diluted  alcohol  and 
subsequent  filtration. 

The  quantity  of  bile  discharged  daily  by  a  grown  person  may  be 
put  at  from  1000  to  1700  c.c.,  or  from  23  to  47  ounces,  but  a  con- 
siderable quantity  of  this  discharged  bile  is  reabsorbed  in  a  changed 
form  by  the  intestines;  only  a  small  amount  of  bile  matters  (in  a 
decomposed  state,  however)  is  contained  in  the  feces. 

Bile  is  to  be  regarded  both  as  a  secretion  and  an  excretion,  as  will 
be  seen  below  in  the  statements  concerning  its  constituents.  It  has 
long  been  believed  that  bile  is  an  intestinal  antiseptic.  Its  action  is, 
however,  weak  and  probably  unimportant,  as  it  has  been  found  that 
certain  bacteria  (B.  typhosus,  B.  coli)  grow  well  in  media  containing 
bile. 

Biliary  pigments.  Several  pigments  have  been  found  in  bile,  but 
it  is  probable  that  only  two,  bilirubin  and  biliverdin,  occur  in  normal 
bile. 

The  bile-pigments  are  formed  in  the  liver  from  haemoglobin  by  a 
process  in  which  the  iron  is  split  off  and  retained  in  the  organism. 
While  the  pigments  of  the  bile  are  regarded  as  waste  products  of 
metabolism,  a  certain  portion  of  them  is  absorbed  in  the  intestine,  is 
excreted  again  by  the  liver,  and  also  by  the  kidneys  (as  urochrome 
and  urobilin).  That  portion  which  passes  out  with  the  feces  is  re- 
duced to  stercobilin  (isomeric  with  urobilin). 


DIGESTION.  685 

Bilirubin,  C16H18N2O3,  is  a  reddish-yellow  pigment  derived  from 
hsematin,  which  it  resembles.  It  is  sparingly  soluble  in  water, 
alcohol,  and  ether,  readily  soluble  in  hot  chloroform  and  carbon 
disulphide. 

Biliverdin,  C32H36N4O8,  is  a  green  powder  existing  in  green  biles  ; 
it  is  formed  from  bilirubin  by  mild  oxidation. 

Tests  for  biliary  coloring-matters.  A  reaction  known  as  Gmelin's 
test  may  be  applied  in  different  ways  : 

1.  Place  into  a  test-tube  a  few  c.c.  of  a  chloroform  solution  of 
bilirubin,  and   pour  down  the   side  of  the  inclined  tube  an  equal 
volume  of  yellow  nitric  acid  in  such  a  manner  that  the  liquids  do 
not  mix.     At  the  line  of  junction  colored  rings  appear,  being  green 
nearest  the  solution  of  the  coloring-matter,  and  progressively  blue, 
violet,  red,  and  yellow.     (Plate  VIII.,  7.) 

2.  Place  on  a  white  porcelain  slab  a  few  drops  of  the  solution  and 
alongside  of  it  a  drop  of  yellow  fuming  nitric  acid.     On  causing 
the  two  liquids  to  come  in  contact  a  play  of  colors  as  above  is  seen 
at  the  junction. 

3.  Expose  an  alkaline  solution  of  bilirubin  to  the  air  in  an  open 
vessel  ;  it  turns  green,  owing  to  the  formation  of  biliverdin.     The 
latter  answers  also  to  Gmelin's  test. 


Biliary  acids.  Glycocholic  acid,  C^H^NOg,  and  taurocholic  acid, 
C26H45NO7S,  exist  as  sodium  salts  in  the  bile^bf  man  and  most 
animals.  Both  salts  may  be  obtained  as  colorless  crystals,  which 
dissolve  in  water,  forming  solutions  with  an  acid  reaction  and  an 
intensely  bitter  taste.  Both  acids  are  easily  decomposed  by  heating 
with  alkalies  or  with  dilute  acids,  also  by  the  action  of  putrefying 
material  or  by  chemical  changes  taking  place  in  the  intestines.  In 
all  these  cases  are  formed  cholic  acid,  C24H40O2,  and  a  second  product, 
which  in  the  case  of  glycocholic  acid  is  glycocoll,  amino-acetic  acid, 
CH2.NH2.CO2H,  and  in  the  case  of  taurocholic  acid,  taurine,  amino- 
ethyl-sulphonic  acid,  NH2.C2H4.SO3H. 

These  acids  are  formed  in  the  liver,  and  very  likely  from  some 
protein  material  ;  the  mode  of  formation  is,  however,  not  known.  As 
in  the  case  of  the  bile-pigments,  the  bile  acids  in  part  represent  waste 
material,  while  a  part  is  reabsorbed  by  the  intestine.  The  physio- 
logical activity  of  bile  acids  is  concerned  mainly  with  the  fats  ;  they 
aid  the  saponification  by  lipase,  and  promote  the  absorption  of  fat 
(probably  by  their  solvent  action).  They  are  believed  to  hold  the 
cholesterin  of  the  bile  in  solution. 


686  PHYSIOLOGICAL  CHEMISTRY. 

Test  for  biliary  acids.  The  biliary  acids  and  their  salts  show  a 
characteristic  reaction  known  as  Pettenkofer's  test.  This  reaction  is 
shown  by  adding  very  little  cane-sugar  to  the  liquid  substance  under 
examination,  and  adding  concentrated  sulphuric  acid  in  such  a 
manner  that  the  temperature  does  not  rise  above  70°  C.  (158°  F.). 
In  the  presence  of  biliary  acids  a  beautiful  cherry-red  color  is  devel- 
oped, which  gradually  changes  to  dark  reddish-purple.  The  red 
liquid  when  examined  spectroscopically  shows  two  absorption-bands, 
one  at  F,  the  other  near  E,  between  D  and  E.  Bile  acids  are  not 
the  only  substances  which  show  the  colors  of  Pettenkofer's  test,  but 
the  spectroscopic  examination  will  clear  up  doubtful  cases. 

Experiment  84.  Evaporate  ox-bile  to  a  thick  syrup,  digest  it  with  5  parts  of 
pure,  cold  alcohol  for  two  hours,  and  filter.  Mix  the  filtrate,  which  contains 
sodium  glycocholate  and  taurocholate,  with  freshly  prepared  animal  charcoal, 
boil  and  filter ;  evaporate  to  dryness  in  a  water-bath,  redissolve  in  the  smallest 
possible  amount  of  pure  alcohol,  and  add  ether  until  the  solution  becomes 
markedly  turbid.  A  white,  crystalline  mass  is  deposited  in  a  few  hours  or  days ; 
this  is  known  as  Planner's  crystallized  bile,  and  is  a  mixture  of  the  two  sodium 
salts  mentioned. 

Dissolve  the  mass  in  a  small  volume  of  water,  adding  a  little  ether  and  then 
dilute  sulphuric  acid;  glycocholic  acid  crystallizes  out  in  shining  needles. 
Taurocholic  acid  is  easiest  prepared  by  using  -dog's  bile,  which  contains  no 
glycocholic  acid. 

Apply  the  Pettenkofer  test  to  the  glycocholic  acid  obtained. 

Cholesterin  and  lecithin  in  the  bile  are  present  in  considerable 
amount.  They  are  regarded  here  as  waste  products. 

Siiiary  calculi  consist  chiefly  of  cholesterin,  and  in  addition  they 
contain  bile-pigment,  the  bile  acids  combined  with  calcium,  calcium 
soaps,  and  calcium  carbonate. 

Experiment  85.  (Examination  of  biliary  calculi.}  Boil  the  freshly  powdered 
stones  with  water  to  remove  bile,  filter,  and  extract  the  dry  residue  with  a 
mixture  of  alcohol  and  ether.  Filter,  and  evaporate  the  filtrate  to  a  small 
volume,  when  crystals  of  cholesterin  will  be  deposited.  Purify  the  crystals  by 
dissolving  them  in  boiling  alcohol  to  which  a  fragment  of  sodium  hydroxide 
has  been  added,  and  treating  the  mixture  in  a  separatory  funnel  with  ether. 
By  evaporation  of  the  ethereal  solution  cholesterin  is  obtained  in  a  pure  con- 
dition. Apply  the  tests  for  the  same  (see  Index). 

The  residue  of  the  calculi,  insoluble  in  ether  and  alcohol,  consists  of  the 
inorganic  salts  and  bile-pigments.  Dissolve  the  salts  by  pouring  dilute  hydro- 
chloric acid  over  the  contents  in  the  filter,  and  show  in  filtrate  the  presence  of 
calcium  by  neutralizing  with  ammonia,  acidifying  with  acetic  acid,  and  adding 
ammonium  oxalate,  when  calcium  oxalate  is  precipitated.  To  a  portion  of  the 
hydrochloric  acid  solution  add  potassium  ferrocyanide ;  sometimes  a  red  pre- 
cipitate is  formed,  due  to  the  presence  of  traces  of  copper  in  the  calculus. 


DIGESTION.  687 

The  residue  left  on  the  filter  consists  of  bilirubin.  Purify  it  by  washing 
with  water,  drying,  and  heating  the  mass  with  chloroform.  On  filtering  and 
evaporating  the  solution  in  a  watch-glass  rhombic  plates  or  prisms  of  bilirubin 
are  left,  which  examine  microscopically,  and  to  which  apply  the  tests  men- 
tioned above. 

Succus  entericus.  The  small  intestine  secretes  several  important 
enzymes  :  erepsin,  which  acts  mainly  upon  the  proteoses  and  peptones, 
splitting  them  into  peptides  and  amino-bodies;  inverting  enzymes  act- 
ing upon  the  disaccharides  (invertase,  maltase,  lactase) ;  and  entero- 
kinase,  which  is  necessary  for  tryptic  digestion.  In  addition  the 
small  intestine  forms  the  prosecretin,  from  which  the  stimulating 
hormone  secretin  is  derived  and  carried  to  the  pancreas.  The  succus 
intestinalis  is  alkaline,  and  aids  in  neutralizing  the  acid  from  the 
stomach. 

Fermentative  and  putrefactive  changes.  In  addition  to  the 
alterations  brought  about  by  the  digestive  enzymes,  the  food  also 
undergoes  fermentative  and  putrefactive  changes,  due  to  the  action 
of  bacteria,  always  present  in  the  intestine.  Some  of  these  bacteria 
convert  carbohydrates  into  acetic,  butyric,  lactic,  and  succinic  acids, 
while  carbon  dioxide,  methane,  and  hydrogen  are  also  liberated. 
Certain  fats  probably  form  neurine  and  similar  toxic  substances. 
By  putrefaction  of  proteins  are  formed  :  phenol,  several  aromatic 
derivatives,  notably  indole  and  skatole,  volatile  fatty  acids,  carbon 
dioxide,  methyl-mercaptan,  and  hydrogen  sulphide. 

As  intermediate  products,  the  bacteria  convert  to  some  extent  the 
food  material  into  the  same  substances  which  are  formed  by  the 
action  of  pancreatic  juice ;  these  products,  however,  are  not  useful 
to  the  organism,  but  are  only  intermediate  stages  of  far-reaching 
decompositions.  The  end-products  of  bacterial  action  pass  out  of 
the  intestine  in  the  feces  and  as  flatus,  or  are  absorbed  and  carried 
to  the  liver,  where  most  of  the  aromatic  compounds  are  conjugated 
with  potassium  acid  sulphate,  and  in  this  form  are  secreted  in  the 
urine.  Thus  the  quantity  of  aromatic  sulphates  in  the  urine  is  a 
measure  of  putrefaction  in  the  intestine. 

Absorption  in  the  small  intestine.  It  seems  advisable  under 
this  heading  to  follow  in  outline  the  foodstuffs  from  their  ingestion 
to  their  delivery  into  the  circulation. 

The  carbohydrates  are  first  acted  upon  by  the  saliva,  ptyalin  split- 
ting the  starches  into  maltose,  and  maltase  splitting  the  maltose  into 
dextrose.  While  this  action  continues  for  some  time  in  the  cardiac 
end  of  the  stomach,  it  is,  in  all,  not  very  extensive.  There  is  no 


688  PHYSIOLOGICAL   CHEMISTRY. 

gastric  enzyme  acting  upon  carbohydrates,  but  a  small  amount  of  the 
simple  sugars  may  be  absorbed  here.  In  the  intestine  the  starches 
are  energetically  attacked  by  the  amylopsin  (diastase)  of  the  pancreas, 
and  the  disaccharides  are  converted  into  the  monosaccharides  by  the 
inverting  enzymes  of  the  succus  entericus.  In  this  manner  almost 
all  of  the  starch  and  sugar  of  the  food  is  normally  reduced  to  the 
hexose  form,  the  greater  part  being  dextrose,  with  some  laevulose, 
galactose,  and  pentose  (from  cane-sugar,  milk-sugar,  and  various  vege- 
tables respectively).  These  simple  sugars  are  absorbed  by  the  small 
intestine,  transferred  as  such  to  the  blood-stream,  carried  directly  to 
the  liver  by  the  portal  vein,  and  here  stored  up  as  glycogen.  If  an 
excessive  amount  of  sugar,  particularly  a  simple  sugar,  be  eaten,  it  is 
absorbed  more  rapidly  than  the  organism  is  able  to  care  for  it,  and  it 
will  appear  unchanged  in  the  urine  (alimentary  glycosuria,  Icevulo- 
suria,  etc.).  The  exact  mechanism  of  this  fact  is  not  known.  It  is 
commonly  believed  that  the  liver  is  unable  to  convert  more  than  a 
certain  amount  of  sugar  into  glycogen,  hence  there  results  an  exces- 
sive quantity  of  sugar  in  the  blood,  which  excess  is  excreted  by  the 
kidneys.  The  amount  of  sugar  which  can  be  eaten  at  one  time  with- 
out a  resulting  excretion  is  termed  the  assimilation  limit  of  that  sugar. 
The  assimilation  limit  differs  for  the  different  sugars  and  in  different 
individuals. 

Fats  undergo  less  digestive  change  than  either  carbohydrates  or 
proteins.  Their  digestion  occurs  mainly  in  the  intestine,  and  consists 
primarily  of  a  saponification  into  glycerin  and  fatty  acid  by  the  lipase 
of  the  pancreas.  The  biliary  fatty  acids  combine  with  the  alkali  of 
the  intestinal  contents  to  form  soaps,  which  produce  an  emulsification 
of  the  neutral  fat  still  present.  This  emulsification  is  believed  to  be 
of  importance  in  offering  a  greater  surface  of  fat  for  the  action  of  the 
lipase.  The  bile  has  two  important  actions  in  fat  digestion,  the  bile 
salts  aid  the  action  of  the  lipase  and  also  act  as  solvents  for  both  the 
fatty  acids  and  the  soaps.  It  is  believed  now  that  little  or  no  fat  is 
absorbed  in  the  form  of  an  emulsion,  and  that  the  greater  part  is 
taken  up  as  glycerin  and  fatty  acid  (soap).  The  glycerin  is,  of 
course,  readily  soluble,  while  the  fatty  acid  is  very  likely  in  solution 
with  the  bile  salts.  Apparently  the  glycerin  and  fatty  acid  are  at 
once  resynthesized  in  the  mucous  membrane  of  the  intestine  to  neutral 
fat  and  passed  into  the  lacteals  as  an  emulsion,  which,  in  turn,  is 
carried  to  the  general  circulation  by  the  thoracic  duct. 

Proteins  are  digested  by  three  enzymes,  pepsin  (stomach),  trypsin 
(pancreas),  and  erepsin.  The  three  carry  out  what  is  fundamentally 


DIGESTION.  689 

the  same  process.  The  pepsin  action  is  exerted  mainly  to  effect  the 
earlier  actions,  i.  e.,  the  change  from  protein  through  primary  and 
secondary  proteose  to  peptone  ;  the  erepsin  is  concerned  mainly  with 
the  later  transformation  from  peptone  to  polypeptide  and  amino- 
bodies  (arnino-acids),  while  the  action  of  trypsin  is  important  through- 
out the  entire  decomposition.  The  general  course  and  ultimate  results 
of  protein  digestion  are  now  fairly  clear,  and  it  is  universally  accepted 
that  proteins  are  absorbed  in  the  form  of  the  amino-bodies  or,  perhaps, 
in  part  as  fairly  simple  polypeptides,  the  protein  nuclei  of  Abder- 
halden.  The  digestion  of  protein  is  believed  to  have  a  deeper  signifi- 
cance than  (as  in  the  case  of  the  carbohydrates  and  fats)  the  mere  pro- 
duction of  soluble  and  dialyzable  substances.  As  the  protein  material 
absorbed  by  the  intestine  is  converted  again  to  protein,  and  as  the 
ingested  (foreign)  protein  must  give  rise  to  a  different  (native) 
protein,  it  is  easy  to  see  that  this  change  must  be  much  more  readily 
carried  out  if  the  foreign  protein  is  first  split  into  its  component  parts, 
the  amino-bodies.  Abderhalden  believes  that  not  all  the  protein  is 
necessarily  split  entirely  to  amino-acids,  but  part  may  remain  in  the 
polypeptide  form  and  serve  as  a  nucleus  to  which  the  other  amino- 
bodies  may  be  added  which  are  needed  for  the  production  of  the 
native  protein.  The  native  protein  thus  formed  is  conveyed  by  the 
portal  system  to  the  liver. 

Absorption  in  large  intestine.  As  the  large  intestine  secretes  no 
enzymes,  the  only  digestive  action  here  is  due  to  the  enzymes  which 
have  been  brought  down  from  above.  This  is  probably  not  of  any 
great  moment,  as  experimental  work  has  shown  that,  with  the  excep- 
tion of  water,  there  is  little  absorption  by  the  large  intestine.  It  is, 
however,  true  that  clinical  work  with  rectal  feeding  shows  that  per- 
sons may  be  sustained  to  a  certain  extent  by  rectal  injections  of  pre- 
digested  food  mixtures. 

Feces  consist  of  the  unabsorbed  material  from  the  food,  the  waste 
material  excreted  from  the  blood,  detached  epithelium,  and  the  secre- 
tions of  the  intestine.  The  odor  depends  largely  on  the  indole  and 
skatole,  to  a  less  degree  on  valeric  and  butyric  acids,  and  on  hydro- 
gen sulphide  present.  The  quantity  and  composition  of  feces  passed 
depend  on  the  nature  of  the  food  and  the  energy  of  the  digestive 
powers.  A  grown  person  in  normal  condition  discharges  from  100 
to  250  grammes  (4  to  9  ounces)  daily.  A  diet  rich  in  animal  proteins 
causes  the  quantity  of  feces  to  be  small,  while  a  diet  rich  in  vegetable 
44 


. 

. 

.     77.  3  per  cent. 
23        " 

es 

biliary, 
residue 

and  coloring-matters    . 
of  food 

.      5.4 
.      1.8        " 
.       1.5        « 
.      1.8 
.      5.2 
4.7 

690  PHYSIOLOGICAL   CHEMISTRY. 

and  starchy  foods  increases  the  quantity.     An  approximate  analysis 
of  the  feces  of  a  healthy  adult  shows : 

Water 

Mucin 

Proteins 

Extractives 

Fats 

Salts 


The  proteins,  other  than  mucin,  are  chiefly  keratins  and  nucleins. 
The  principal  salts  are  ammonium-magnesium  phosphate,  calcium 
carbonate,  calcium  and  magnesium  phosphate.  The  bile-pigment 
normally  is  stercobilin,  derived  from  bilirubin  by  reduction. 

A  large  proportion  of  the  feces  consists  of  bacteria.  The  micro- 
scopic examination  of  feces  for  intestinal  parasites  and  bacteriological 
examinations  are  of  great  value  in  clinical  work.  The  significance 
of  the  chemical  findings  are  not  yet  well  understood  except  in  a  few 
instances  (e.  g.,  presence  of  blood  and  bile). 

Experiment  86.     (Chemical  examination  of  feces.} 

a.  Reaction.    Normally  the  reaction  of  feces  is  slightly  alkaline  to  litmus. 

b.  Fat.    Extract  the  feces  with  ether  and  evaporate  the  ethereal  solution. 
Mix  a  portion  of  the  residue  with  potassium  acid  sulphate  and  ignite  ;  in  the 
presence  of  neutral  fat  the  characteristic  odor  of  acrolein  is  noticed.     Dissolve 
another  portion  of  the  residue  in  a  mixture  of  alcohol  and  ether  which  has 
been  colored  blue-violet  by  alkanet  (a  dye  derived  from  a  plant  of  the  same 
name,  and  used  as  .an  indicator  for  certain  acids) ;  a  red  color  indicates  the 
presence  of  fatty  acids.    (The  occurrence  of  large  amounts  of  fats  or  fatty  acids 
in  the  feces  may  be  the  result  of  the  ingestion  of  an  excessive  quantity  of  fat, 
or  of  imperfect  digestion  and  absorption  due  to  pathological  conditions.) 

c.  Mucin.    Mix  the  feces  with  lime-water,  allow  to  stand  for  several  hours, 
filter,  and  acidify  filtrate  with  acetic  acid.     A  precipitate  indicates  mucin.     To 
verify  the  nature  of  the  precipitate,  boil  it  with  dilute  hydrochloric  acid  for  an 
hour,  then  neutralize,  and  heat  with  Fehling's  solution.     A  red  precipitate 
proves  the  substance  to  have  been  mucin.     (Mucin  occurs  in  the  feces  in  con- 
siderable quantity  whenever  there  is  catarrh  of  the  large  intestine,  and  in  cases 
of  membranous  enteritis.) 

d.  Albumin.    Mix  the  feces  with  water,  acidify  with  acetic  acid,  and  filter, 
est  the  clear  filtrate   by  adding  potassium  ferrocyanide.     Albumin,  when 

present,  coagulates.     (Albumin  is  found  in  the  feces  of  typhoid  fever  patients.) 

e.  Proteose  and  peptone.     Make  a  thin  paste  of  feces  with  water,  boil,  and 
;er  while  hot.     To  the  filtrate  add  lead  acetate,  filter,  and  apply  the  biuret 

aon.     (Proteose  and  peptone  are  found  in  the  feces  whenever  much  pus  is 
produced  in  the  intestine.) 

/   Carbohydrates.     Boil  the  residue,  left  from  the  extraction  with  ether  (6), 


DIGESTION.  691 

with  water,  filter,  and  evaporate  filtrate  to  a  small  volume.  Test  the  liquid  for 
sugar  with  Fehling's  solution,  and  for  dextrin  and  starch  with  iodine. 

g.  Blood.  When  the  blood  in  the  feces  is  derived  from  the  lower  portion 
of  the  intestine  the  red  color  is  so  characteristic  that  further  examination  is 
unnecessary.  When  the  blood  comes  from  the  upper  intestine  and  the  pig- 
ment has  been  altered,  it  becomes  necessary  to  make  a  spectroscopic  examina- 
tion or  the  ha3min  test,  for  which  see  page  658.  For  the  spectroscopic  exami- 
nation, the  feces  are  extracted  with  water  containing  a  little  acetic  acid,  and 
the  liquid  is  extracted  with  ether.  If  blood  is  present,  the  ethereal  solution 
is  brownish  red.  Evaporate  the  solution  to  dryness  and  dissolve  the  residue  in 
water  containing  a  little  sodium  hydroxide.  The  solution  is  haematin  in  alka- 
line solution,  and  will  show  the  characteristic  bands,  Fig.  72,  e.  Hrematin  may 
occur  in  feces  physiologically  as  a  result  of  a  meat  diet ;  pathologically,  it  is' 
found  after  hemorrhage  into  the  intestine  from  any  source. 

Occult  blood  is  the  name  given  to  traces  of  blood  occurring  in  the  feces  after 
small  hemorrhages  from  ulcer  of  the  stomach  or  duodenum.  Its  presence  is 
shown  as  follows :  Extract  10  grammes  of  feces  with  25  c.c.  of  ether  to  remove 
fat.  To  the  residue  add  5  c.c.  of  glacial  acetic  acid  and  then  extract  again 
with  20  c.c.  of  ether.  To  this  ethereal  extract  add  a  little  powdered  guaiac 
and  then  1  or  2  c.c.  ozonized  turpentine.  A  blue  color  develops  on  shaking 
and  standing,  rendered  more  intense  by  the  addition  of  chloroform. 

Klunge's  aloin  test  may  be  used  in  place  of  the  guaiac  reaction.  Mix  the 
acetic  acid  and  ether  extract  of  feces,  obtained  as  above,  with  1  or  2  c.c.  of  tur- 
pentine, and  add  immediately  about  1  c.c.  of  a  2  per  cent,  solution  of  aloin  in 
70  per  cent,  alcohol.  In  the  presence  of  blood  the  fluid  rapidly  becomes  bright 
red  in  color. 

h.  Bile-pigments.  Shake  the  feces  with  a  saturated  solution  of  mercuric 
chloride,  filter,  and  add  chloroform.  A  rose  color  develops  at  the  junction  of 
the  fluids  in  the  presence  of  urobilin,  which  is  the  normal  bile-pigment  of 
feces.  (The  absence  of  bile-pigment  in  the  feces  indicates  disease  of  the  liver 
or  obstruction  to  the  flow  of  bile.) 

Extract  feces  with  chloroform,  and  to  the  chloroform  solution  apply  Gmelin's 
test  for  bile-pigments.  (The  presence  of  bilirubin  or  biliverdin  in  the  stools 
of  adults  indicates  catarrh  of  the  intestine.) 

i.  Bile  acids.  Extract  feces  with  alcohol  and  evaporate  the  filtrate  to  dryness. 
Dissolve  the  residue  in  water  containing  a  little  sodium  hydroxide,  and  to  the 
solution  apply  Pettenkofer's  test.  (Normally,  bile  acids  are  completely  absorbed, 
therefore  their  presence  in  feces  is  pathological.) 

j.  Ferments.  Extract  the  feces  with  glycerin,  precipitate  the  solution  with 
alcohol,  and  dissolve  the  precipitate  in  water.  To  part  of  the  solution  add  a 
little  starch  paste,  keep  the  mixture  at  40°  C.  (104°  F.)  for  several  hours,  and 
test  for  glucose.  A  positive  test  indicates  the  presence  of  diastatic  enzyme. 
Digest  another  portion  of  the  solution  at  the  stated  temperature  with  coagu- 
lated protein  and  a  little  sodium  carbonate.  Filter  and  apply  the  biuret 
reaction,  which,  if  positive,  indicates  the  presence  of  proteolytic  ferment. 
(The  various  digestive  enzymes  are  found  in  the  feces  when  there  is  diarrhoea 
resulting  from  inflammation  of  the  upper  intestine.) 

Jc.  Inorganic  constituents  are  determined  in  the  usual  manner  after  drying  and 
incinerating  the  feces.  Present  are  chiefly  earthy  phosphates,  silica,  sodium 
chloride  and  sulphate,  iron  compounds,  etc. 


692  PHYSIOLOGICAL   CHEMISTRY. 

Fecal  calculi.  Feces  sometimes  contain  hard  masses,  known  as 
coproliths  and  enteroliths.  Coproliths  are  inspissated  feces.  Entero- 
liths  usually  consist  of  concentric  layers  of  earthy  phosphates  and 
insoluble  soaps  around  a  nucleus  of  a  piece  of  bone,  a  fruit-stone, 
etc.  Pancreatic  stones  consist  of  calcium  phosphate  and  carbonate 
without  cholesterin  or  bile-pigment.  Intestinal  sand  is  the  name 
given  to  certain  small  calculi  occurring  in  the  feces.  They  are  com- 
posed of  magnesium  and  calcium  soaps,  cholesterin,  bile-pigment, 
salts  of  magnesium,  and  some  of  the  hydroxy  acids,  such  as  succinic 
acid.  The  clinical  significance  of  these  concretions  is  not  definitely 
known. 

The  liver.  The  anatomical  relations  of  the  liver  indicate  the  im- 
portance of  this  organ  in  assimilation,  digestion,  and  excretion.  The 
digestive  function  of  the  liver,  which  is  comparatively  slight,  and  the 
excretory  function  are  carried  out  largely  by  means  of  the  bile.  The 
digestive  properties  of  bile  have  been  considered. 

While  it  is  probable  that  the  liver  has  some  action  on  the  protein 
material  brought  to  it  by  the  portal  system  directly  after  its  digestion 
and  absorption  in  the  intestine,  this  has  not  been  proved.  It  is,  how- 
ever, known  that  the  main  nitrogenous  excretion  of  the  body,  the 
urea  of  the  urine,  is  formed  here,  and  is  merely  excreted  by  the 
kidneys.  The  mechanism  of  this  urea  production  is  not  clear.  It  is 
likely  that  the  waste  nitrogen  is  brought  to  the  liver  in  the  form  of 
ammonium  salts  (carbonate  or  carbamate),  and  by  it  is  transformed 
into  urea.  Liver  tissue  has  the  power  of  producing  such  a  change 
under  experimental  conditions,  but  it  has  not  been  proved  that  the 
process  occurs  normally  in  this  manner.  In  birds  the  main  nitrog- 
enous excretion,  uric  acid,  has  also  been  shown  to  be  formed  in  the 
liver. 

Glycogen  is  one  of  the  most  important  constituents  of  the  liver,  and 
undoubtedly  represents  a  storage  supply  of  carbohydrate  material.  It 
is  derived  for  the  most  part  directly  from  the  carbohydrates  of  the 
food  which  have  been  split  in  the  intestine,  absorbed  as  dextrose  and 
laevulose,  and  carried  directly  to  the  liver  by  the  portal  vein.  Here 
these  simple  sugars  are  converted  into  the  more  complex  glycogen  by 
a  process  of  dehydration.  It  is  probable  that  some  of  the  simple  as 
well  as  the  conjugate  proteins  can  also  form  sugar  and,  hence,  gly- 
cogen. Some  of  the  sugar  excreted  in  diabetes  is  certainly  derived 
from  the  proteins.  It  is  not  clear,  however,  that  such  a  change  takes 
place  under  normal  conditions.  The  question  with  regard  to  the  fats 
is  in  somewhat  the  same  condition.  It  has  been  shown  that  glycogen 


DIGESTION.  693 

can  be  derived  from  glycerin  ;  hence  it  can  be  derived  from  the  fats 
which  contain  glycerin,  but  whether  it  is  normally  derived  from  the 
fats  is  not  known.  When  the  tissues  are  in  need  of  sugar  to  supply 
them  with  a  source  of  energy,  the  glycogen  of  the  liver  is  split  and 
is  distributed  by  the  blood-stream  in  the  form  of  dextrose.  This  is 
seen  especially  clearly  in  the  case  of  the  muscles,  which  require  a 
large  amount  of  sugar,  and  have  also  the  power  of  storing  up  a  local 
supply  very  much  as  the  liver  stores  up  a  general  supply  for  £he 
whole  body.  It  is  found  that  in  starvation,  and  particularly  in 
starvation  with  extensive  muscular  work,  that  the  store  of  glycogen 
in  both  the  liver  and  the  muscles  is  rapidly  exhausted. 

Indole  and  skatole,  formed   by  putrefaction  in  the  intestine,  are 

brought  to  the  liver  by  the  portal   vein.     Indole,  C6H  /NH  ">CH, 


is  oxidized,  forming  indoxyl,  C8H7NO,  which  combines  with  potas- 
sium acid  sulphate,  with  elimination  of  water,  forming  indoxyl 
potassium  sulphate,  C8H6NKSO4,  which  is  excreted  in  the  urine. 
Skatole,  methyl-indole,  C6H4(CCH3CH)NH,  is  similarly  converted 
into  the  oxidation  product  skatoxyl,  C9H9NO,  and  skatoxyl  potassium 
sulphate,  C9H8NKSO4.  These  substances  appear  in  the  urine  as  the 
conjugate  or  ethereal  sulphates. 

The  formation  of  glycogen  from  sugar  has  been  mentioned,  and  its  physical 
properties  were  considered  in  Chapter  48. 

Experiment  87.  (Preparation  of  glycogen.}  Digest  50  grammes  of  fresh  liver 
with  500  c.c.  of  boiling  water  containing  about  5  c.c.  of  acetic  acid.  Strain 
the  liquid  through  muslin.  The  solution  contains  besides  glycogen  some  pro- 
tein, which  remove  by  concentrating  the  liquid  to  a  small  volume  and  adding 
alternately  a  few  drops  of  hydrochloric  acid  and  of  potassium  mercuric  iodide 
as  long  as  a  precipitate  is  formed.  Filter  and  mix  filtrate  with  2  volumes  of 
alcohol,  when  glycogen  is  precipitated  ;  purify  it  by  pouring  off  the  super- 
natant liquid  and  washing  it  with  65  per  cent,  alcohol  by  decantation.  Then 
cover  with  absolute  alcohol,  let  stand  for  an  hour,  collect  the  glycogen  on  a 
filter,  and  dry  between  filter-paper. 

Tests  for  glycogen. 

1.  Dissolve  some  glycogen  in  warm  water  :  an  opalescent  solution 
resembling  soluble  starch  solution  is  formed. 

2.  To  a  portion  of  solution  add  iodine  solution  :  a  reddish-brown 
color  resembling  the  one  produced  by  erythrodextrin  is  produced. 

3.  Heat  some  of  the  solution  with  Fehling's  solution  :  no  change 
occurs. 

4.  Acidify  solution  with  hydrochloric  acid,  boil  a  few  minutes, 


694  PHYSIOLOGICAL   CHEMISTRY. 

cool,  and  neutralize.  Divide  solution,  and  heat  one  portion  with 
Fehling's  solution,  when  the  formation  of  a  red  precipitate  indicates 
the  conversion  of  glycogen  into  dextrose.  To  the  second  portion  add 
iodine  :  no  change. 

5.  To  some  glycogen  solution  add  about  half  its  volume  of  saliva, 
keep  the  mixture  at  40°  C.  (104°  F.)  for  about  ten  minutes,  and  test 
part  of  solution  with  iodine,  the  other  portion  with  Fehling's  solu- 
tion. The  results  show  that  glycogen  has  been  changed  as  in 
previous  test. 

The  liver  has  also  a  neutralizing  function,  by  virtue  of  which  it 
retains  and  renders  innocuous  various  toxins  and  putrefactive  pro- 
ducts which  are  absorbed  by  the  intestine. 

57.  MILK. 

General  properties.  Milk  is  the  secretion  of  the  mammary 
glands,  the  presence  of  which  is  characteristic  of  mammalia.  The 
milk  of  different  animals  differs  somewhat  in  composition,  but  it 
always  contains  all  the  constituents  necessary  for  a  normal  develop- 
ment of  the  various  tissues,  liquids,  organs,  etc.,  of  the  young 
mammal,  which  generally  feeds  exclusively  upon  milk  for  a  shorter 
or  longer  period  of  its  early  life. 

Milk  is  an  opaque,  aqueous  solution  of  casein,  albumin,  lactose,  and 
inorganic  salts,  holding  in  suspension  small  globules  of  fat,  invested, 
most  likely,  with  coatings  of  casein  or  with  some  other  albuminous 
envelope.  The  reaction  of  woman's  milk  and  that  of  the  herbivora 
is  normally  alkaline,  but  that  of  carnivora  is  acid.  Its  specific 
gravity  ranges  from  1.029  to  1.033,  but  may  in  extreme  cases  vary 
between  1.018  and  1.045. 

Experiment  88.  a.  Examine  milk  microscopically ;  notice  the  variously  sized 
globules  of  fat,  and  compare  the  appearance  of  milk,  cream,  and  skimmed  milk. 

b.  Test  with  sensitive  litmus-paper  the  reaction  of  fresh  cows'  milk  and  of 
milk  that  has  been  exposed  to  the  air  for  a  day  or  two.  The  former  will  be 
alkaline  or  amphoteric,  due  to  the  presence  of  mono-  and  di-calcium  phos- 

QUESTIONS.— What  is  the  active  principle  of  saliva,  and  how  does  it  act  on 
starch?  Explain  the  process  of  the  absorption  of  protein.  State  the  compo- 
sition of  gastric  juice,  explain  its  physiological  action,  and  describe  methods 
for  determining  its  chief  constituents.  What  substances  are  formed  during  the 
conversion  of  a  simple  protein  into  peptone?  What  are  the  functions  of  ^pan- 
creatic juice?  State  the  composition  of  the  different  kinds  of  calculi  found  in 
feces.  How  are  fats  digested  and  absorbed  ?  State  the  general  properties  of 
bile  and  mention  its  chief  constituents ;  describe  Gmelin's  and  Pettenkofer's 
tests.  What  are  the  principal  constituents  of  feces  ?  State  properties  and  re- 
actions of  glycogen. 


MILK. 


695 


phate ;   the  latter  will  be  acid,  because  lactic  acid  has  been  formed  by  the 
fermentation  of  milk-sugar. 

c.  Boil  some  fresh  milk;  no  coagulum,  but  a  scum  is  formed.  After  re-, 
moval  of  the  scum  it  is  reformed  on  boiling.  Repeat  the  experiment  with 
milk  that  has  stood  some  time ;  a  coagulum  is  formed. 

Composition.  The  average  composition  of  various  kinds  of  milk 
is  given  below,  but  it  must  be  remembered  that  milk  not  only  differs 
in  certain  species,  but  also  in  the  same  animal  at  different  times ; 
for  instance,  the  quality  and  quantity  of  food  taken,  as  also  various 
physiological  changes,  have  decided  influence  upon  the  milk  secreted. 


Human  milk. 


Cows'  milk. 


Variations.        Average. 

Variations.        Average. 

Water     . 

90.8  to 

85.3 

88.30 

90.2  to  83.7 

86.70 

Casein  and  albumin 

1.4  to 

2.5 

2.00 

3.3  to 

5.5 

4.40 

Fat  (butter)    . 

3.0  to 

3.8 

3.40 

2.8  to 

4.5 

3.65 

Lactose 

4.0  to 

8.0 

6.00 

3.0  to 

6.0 

4.50 

Inorganic  salts 

0.2  to 

0.4 

0.30 

0.7  to 

0.8 

0.75 

Goat. 

Sheep. 

Ass. 

Mare. 

Cream. 

Water    . 

86.0 

83.3 

90.6 

90.6 

56 

to  71 

Casein  and  albumin 

3.8 

5.4 

2.7 

2.2 

4 

to    3 

Fat  (butter)  . 

5.2 

5.3 

1.0 

1.1 

35 

to  22 

Lactose 

4.3 

5.2 

5.3 

5.8 

4 

to    3 

Inorganic  salts 

0.7 

0.8 

0.4 

0.3 

0.7 

to  0.7 

Skimmed 
milk. 

Condensed     „   . 
milk. 

Buttermilk.  Curd. 

•   Whey. 

Water    . 

90.6 

25 

15.0 

90.2 

59.4 

93.5 

Casein  and  albumin 

3.1 

14 

2.2 

4.1 

27.7 

0.8 

Fat  (butter)  . 

0.8 

10 

82.0 

1.0 

6.4 

0.3 

Lactose 

4.8 

491 

0.3 

3.7 

5.0 

4.5 

Inorganic  salts     .  . 

0.7 

2 

0.5 

0.7 

1.5 

0.6 

Lactic  acid     . 

.  . 

.  . 

0.3 

.  . 

0.3 

The  inorganic  salts  consist  chiefly  of  calcium  or  sodium  phosphate 
and  sodium  and  potassium  chloride,  but  contain  also  some  magnesium 
and  iron.  The  proteins  consist  mainly  of  casein  with  some  albumin, 
the  proportion  being  in  cows'  milk  about  as  6  to  1,  in  woman's  milk 
as  3  tc  4. 

Besides  the  constituents  mentioned  in  the  above  analyses,  milk  also 
contains  a  very  small  quantity  of  extractives,  among  which  are  found 
urea,  creatine,  lecithin,  citric  acid,  phospho-carnic  acid,  etc.  The 
principles  which  give  to  milk  its  peculiar  odor  have  not  yet  been 
conclusively  pointed  out.  The  gaseous  constituents  of  milk  are 
mainly  carbon  dioxide,  oxygen,  and  nitrogen  :  100  volumes  of  milk 

i  Including  cane-sugar  added  by  the  manufacturer. 


696  PHYSIOLOGICAL  CHEMISTRY. 

contain    of  carbon    dioxide    7.06,   of  oxygen    0.1,  of  nitrogen   0.7 
volumes. 

Milk  contains  several  enzymes,  whose  natures  vary  with  their 
sources.  One  of  these,  an  oxidizing  ferment  (oxidase,  catalase),  is  a 
constant  constituent,  and  is  of  importance  because  its  absence  shows 
that  the  milk  has  been  heated  for  preservation. 

The  presence  of  an  oxidizing  ferment  in  milk  can  thus  be  shown  :  Shake  10 
c.c.  of  milk  with  1  c.c.  of  tincture  of  guaiac,  5  c.c.  oil  of  turpentine,  and  5  c.c. 
of  solution  of  hydrogen  dioxide.  A  blue  color  is  developed  when  the  ferment 
is  present. 

Milk-proteins.  The  proteins  of  milk  are  caseinogen,  lactoglobulin  ^ 
and  ladalbumin.  Lactoglobulin  and  lactalbumin  closely  resemble  the 
globulin  and  albumin  of  the  blood-serum,  and  are  believed  to  be  de- 
rived from  them  with  little  constitutional  change.  Caseinogen  is,  on 
the  other  hand,  a  specialized  protein  containing  phosphorus  and  be- 
longing to  the  group  of  phospho-proteins.  It  is  present  in  milk 
either  in  solution  or  perhaps  in  combination  with  phosphates  in  a 
partially  insoluble  form,  and  this  combination  may  be  responsible  for 
some  of  the  opacity  of  the  milk.  When  milk  is  acted  upon  by  rennin 
there  is  a  coagulation  of  the  caseinogen  and  the  formation  of  a  clot. 
It  may  readily  be  shown  that  this  process  takes  place  in  two  steps. 
First,  the  caseinogen  is  changed  by  the  rennin  to  a  form  called  para- 
casein.  This  substance  remains  in  solution,  and  the  nature  of  the 
change  is  not  understood.  In  the  second  stage  the  paracasein  forms 
a  combination  with  the  calcium  salts  of  the  milk  and  is  precipitated 
as  casein  (calcium-casein).  The  calcium  enters  only  in  the  second 
step  and  has  no  part  in  the  formation  of  paracasein.  The  significance 
of  this  coagulation  of  milk  in  the  stomach  is  not  known.  It  is  fre- 
quently stated  that  a  peptone  is  split  off  from  the  caseinogen  in  the 
production  of  paracasein.  The  process  may  be  hydrolytic  in  nature, 
and  a  preliminary  step  in  the  digestion  of  caseinogen.  As  implied 
above,  no  coagulation  will  take  place  if  the  calcium  salts  be  removed 
from  the  milk. 

Caseinogen  occurs  only  in  milk ;  it  is  a  phospho-protein,  yielding 
on  hydrolysis  a  pseudonuclein.  When  dry  it  is  a  fine,  white  powder, 
insoluble  in  water,  but  soluble  in  dilute  salt  solution  and  in  water 
containing  a  little  alkali. 

Caseinogen  resembles  the  alkali  albuminates  in  dissolving  in  water  in  the 
presence  of  calcium  carbonate  with  evolution  of  carbon  dioxide.  The  solution 
is  precipitated  by  hydrochloric  and  acetic  acids,  the  precipitate  being  soluble 
in  slight  excess,  and  reprecipitated  by  a  large  excess  of  the  acid.  The  solution 


MILK.  697 

in  lime-water  is  not  precipitated  by  phosphoric  acid,  but  an  opaque  fluid  is 
obtained  containing  casein  and  calcium  phosphate  in  suspension.  The  solu- 
tion is  precipitated  by  alum,  zinc  sulphate,  cupric  sulphate,  etc.  Caseinogen 
solutions  are  not  coagulated  by  heat,  but,  like  milk,  are  covered  with  a  scum. 

Experiment  89.  (Preparation  of  casein.}  To  a  mixture  of  400  c.c.  of  milk 
and  1  liter  of  water  add  gradually  enough  (but  not  more)  of  acetic  acid  to  pre- 
cipitate the  casein,  which  also  carries  down  the  fat.  Decant  the  liquid,  then 
filter,  first  through  muslin,  then  through  paper,  reserving  liquid  for  Experi- 
ment 93.  Wash  the  coagulum  well  with  water,  press  it  as  dry  as  possible, 
then  grind  it  with  100  c.c.  of  alcohol,  and  allow  to  stand  for  an  hour.  Filter, 
dry  the  coagulum  between  filter-paper,  place  it  with  200  c.c.  of  ether  into  a 
stoppered  bottle  and  let  stand  for  a  day.  Collect  the  precipitate  on  a  filter  and 
add  filtrate  to  the  alcoholic  filtrate  from  above;  the  mixture  will  be  used  for 
Experiment  92.  Rub  the  casein  in  a  mortar  until  the  ether  is  evaporated. 
To  purify  it  from  fat,  mix  with  water  and  add  drop  by  drop  a  1  per  cent, 
solution  of  sodium  hydroxide  until  the  greater  part  of  the  casein  is  dis- 
solved. The  mixture,  which  should  not  be  alkaline  after  thoroughly  stirring 
it,  is  then  filtered,  when  some  fat  and  suspended  matter  is  left  behind,  while  a 
fairly  clear  filtrate  is  obtained.  Acidify  faintly  with  acetic  acid,  wash  the 
precipitated  casein  with  water,  alcohol,  and  ether,  and  dry  between  paper. 

Tests  for  casein. 

1.  Apply  the  xanthoproteic,  Millon's,  and  biuret  reactions. 

2.  Dissolve  casein  in  a  1  per  cent,  solution  of  sodium  carbonate; 
neutralize  with  acetic  acid,  when  casein  is  precipitated. 

3.  Mix   some  casein   in   a  mortar  with  freshly  precipitated  cal- 
cium carbonate  and  water.     Casein  dissolves,  while  carbon  dioxide 
is  liberated. 

4.  Dissolve  casein  in  lime-water  and  add  dilute  phosphoric  acid 
until   the  solution  is   neutral.     No   precipitate  is  formed,  but  the 
liquid  becomes  turbid. 

5.  Heat  a  mixture  of  casein  with  sodium  carbonate  and  potassium 
nitrate  in  a  crucible  (or  dry  test-tube)  until  all  organic  matter  has 
been  destroyed.     Dissolve  mass  in  water,  acidify  with  nitric  acid, 
filter,  and  add  ammonium  molybdate.    A  yellow  precipitate  is  formed, 
showing  the  presence  of  phosphorus  in  the  casein. 

Experiment  90.  (Separation  of  the  proteins.}  Saturate  20  c.c.  of  fresh  milk  with 
powdered  sodium  chloride:  a  precipitate  consisting  of  caseinogen  and  fat  is 
formed.  Filter,  wash  the  precipitate  with  saturated  solution  of  sodium 
chloride,  rub  the  moist  precipitate  with  20  c.c.  of  water,  allow  to  stand  for 
twenty-four  hours,  and  filter.  The  solution  contains  caseinogen  in  the 
same  condition  in  which  it  is  found  in  milk.  To  a  portion  of  the  solution 
add  acetic  acid :  casein  is  precipitated.  To  another  portion  add  a  solution  of 
rennin  and  some  calcium  chloride,  heat  to  40°  C.  (104°  F.)  for  a  short  time, 
when  a  precipitate  of  paracasein  is  formed. 

Saturate  the  filtrate  from  caseinogen  and  fat  with  magnesium  sulphate : 


698  PHYSIOLOGICAL   CHEMISTRY. 

lactoglobulin  is  precipitated.  The  filtrate  contains  lactalbumin,  which  can  be 
precipitated  by  saturating  the  solution  with  ammonium  sulphate. 

Experiment  91.  (Action  of  rennin  on  milk.}  To  20  c.c.  of  milk  add  4  c.c.  of 
a  0.1  per  cent,  solution  of  rennin,  mix  well,  and  digest  at  40°  C.  (104°  F.). 
A  coagulum  consisting  of  casein  and  fat  soon  forms,  while  an  aqueous  fluid 
(whey),  containing  proteins,  milk-sugar,  salts,  and  extractives,  is  pressed  out. 
After  adding  a  drop  or  two  of  acetic  acid  heat  a  portion  of  the  whey  to  boiling : 
a  voluminous  coagulum  of  simple  proteins  is  formed. 

Eepeat  the  above  experiment  with  milk  from  which,  by  the  addition  of  2 
c.c.  of  a  1  per  cent,  solution  of  ammonium  oxalate,  the  calcium  salts  have 
been  removed.  No  coagulum  occurs  until  calcium  chloride  is  added  in  a 
quantity  sufficient  to  precipitate  any  ammonium  oxalate  left  in  solution,  and 
to  furnish  the  calcium  salt  required  for  precipitation. 

Kepeat  again,  boiling  the  mixture  in  order  to  destroy  the  rennin  before  the 
addition  of  the  calcium  solution ;  clotting  will  occur,  showing  that  calcium  is 
necessary  only  for  the  precipitation,  not  for  the  interaction  between  the  casein- 
ogen  and  the  rennin. 

Milk-fat.  It  has  been  mentioned  above  that  the  fat  of  milk  is 
held  in  suspension  as  small  globules,  which  are  surrounded  by  a 
protein  envelope.  The  latter  prevents  the  solution  of  fat  when 
ether  is  added  directly  to  milk.  If,  however,  a  few  drops  of  caustic 
alkali  be  added  with  the  ether,  then  the  envelope  will  be  destroyed 
and  the  fat  dissolves.  Whenever  a  precipitate  occurs  in  milk  the  fat 
is  carried  down  with  the  insoluble  substance  and  the  envelope  is 
generally  destroyed.  The  fat  of  milk  is  a  mixture  of  the  glycerides 
of  several  fatty  acids,  chiefly  of  palmitic  and  oleic,  with  small  quan- 
tities of  butyric,  caproic,  caprylic,  and  stearic  acids.  Butter  fat  may 
be  recognized  by  liberating  the  butyric  acid,  which  has  a  character- 
istic odor. 

Experiment  92.  (Liberation  of  butyric  acid.)  Use  the  mixed  ethereal  and 
alcoholic  filtrate  from  Experiment  89.  Allow  the  ether  to  evaporate  spon- 
taneously, and  add  to  the  alcoholic  solution  of  butter  fat  about  5  grammes 
of  potassium  hydroxide.  Heat  the  mixture  on  a  water-bath  until  a  drop  of 
it  is  found  to  be  completely  soluble  in  water,  indicating  complete  saponifica- 
tion.  Evaporate  until  odor  of  alcohol  has  disappeared;  add  30  c.c.  of  dilute 
sulphuric  acid,  when  the  fatty  acids  are  set  free  and  butyric  acid  can  be  recog- 
nized by  its  odor. 

Butter.  Even  in  the  thickest  varieties  of  cream  there  is  no  cohe- 
sion between  the  fat  globules,  while  in  butter  the  fat  has  actually 
cohered.  This  change  is  accomplished  by  violently  agitating  (churn- 
ing) the  cream,  when  the  fat  particles  gradually  combine  with  each 
other,  while  the  liquid  (buttermilk)  separates. 

Chemically,  butter  is  a  milk-fat,  containing  a  certain  proportion^ 


MILK.  699 

15  or  16  per  cent.,  of  water,  besides  traces  of  casein,  salts,  coloring- 
matter,  etc.  For  curing  butter,  common  salt  is  often  used ;  the 
quantity  added  should  not  exceed  5  per  cent. 

The  composition  of  buttermilk  has  been  given  above ;  when 
freshly  obtained  from  sweet  cream  it  is  a  pleasant  drink  and  a  whole- 
some food. 

Milk-sugar.  Lactose.  The  general  properties  of  milk-sugar 
have  been  mentioned  on  page  534.  By  hydrolysis  it  yields  two 
simple  sugars,  dextrose  and  galactose ;  when  boiled  with  nitric  acid, 
saccharic  and  mucic  acids  are  formed,  the  latter  being  a  characteristic 
product  of  the  oxidation  of  galactose.  Solutions  of  milk-sugar  are 
dextrorotatory.  Lactose  occurs  occasionally  in  the  urine  of  preg- 
nant women,  and  also  in  the  urine  after  ingestion  of  large  quantities 
of  milk-sugar. 

Experiment  93.  (Preparation  of  milk-sugar.)  Use  the  aqueous  filtrate  obtained 
in  Experiment  89.  Free  the  solution  from  the  remaining  proteins  by  boiling 
and  filtering;  evaporate  to  about  75  c.c.,  when  calcium  phosphate  will  be 
deposited.  Filter,  evaporate  to  a  syrup,  and  set  aside,  when  crystals  of  lactose 
will  be  formed.  The  crystals  may  be  purified  by  treating  their  solution  with 
bone-black  aud  recrystallizing. 

Tests  for  milk-sugar. 

1.  To  solution  of  milk-sugar  apply  Fehling's,  Trornmer's,  Moore's, 
Boetger's,  and  Nylander's  tests,  for  which  see  Index. 

2.  Add  ammonio-silver  nitrate  and  a  drop  of  sodium  hydroxide. 
A  mirror  of  metallic  silver  forms  on  heating  the  mixture. 

3.  Indigo-test.     To  a  dilute  solution  add  enough  indigo-carmine  to 
produce  a  blue  color,  and  render  alkaline  with  sodium  carbonate. 
On  heating,  the  blue  solution  becomes  successively  red,  yellow,  and 
colorless,  or  nearly  so,  in  consequence  of  the  deoxidizing  power  of 
the  lactose.     Pour  the  cooled  solution  repeatedly  from  one  test-tube 
into  another;   the  colors  are  reproduced  in  reverse  order  in  con- 
sequence of  the  absorption  of  oxygen. 

4.  As  grape-sugar  responds  to  the  above  tests,  the  fermentation- 
test  may  be  used  for  distinguishing  between  the  two  sugars.     Fill 
two  fermentation  tubes  with  glucose  and  lactose  solution,  respectively  ; 
add  yeast,  let  stand  in  a  warm  place,  and  notice  that  a  gas  rises  from 
the  glucose,  but  not  from  the  lactose  solution. 


700  PHYSIOLOGICAL  CHEMISTRY. 

Physical  and  chemical  changes  in  milk  on  standing. 

After  leaving  the  body  milk  undergoes  physical  and  chemical 
changes.  The  principal  physical  change  is  the  separation  of  milk 
into  two  layers :  the  upper,  cream,  contains  practically  all  the  fat, 
and  its  proportionate  quantity  of  other  constituents;  the  lower, 
skimmed  milk,  is  almost  fat-free.  By  removing  varying  quantities 
of  skimmed  milk  by  siphon  or  otherwise,  the  proportion  of  fat  in  the 
remainder  of  the  milk  is  increased. 

Of  chemical  change,  occurs,  particularly  on  standing  in  a  warm 
place,  conversion  of  lactose  into  lactic  acid  through  lactic  acid  fer- 
mentation. The  reaction  of  milk  then  becomes  acid,  the  casein  coag- 
ulates and  separates  as  a  solid  white  curd  carrying  with  it  fat.  The 
remaining  thin,  transparent  liquid,  whey,  contains  all  the  inorganic 
salts,  that  portion  of  lactose  which  has  not  been  decomposed,  as  also 
the  lactic  acid  formed. 

There  has  recently  been  an  extensive  use  of  milk  which  has  been 
fermented  by  the  Bacillus  Bulgaricus,  a  powerful  lactic  acid  pro- 
ducer. This  use  has  been  based  upon  the  belief  of  Metchnikoff  that 
acid-producing  bacteria  are  antagonistic  to  the  putrefactive  bacteria 
which  are  normally  present  in  the  intestine,  hence  the  milk  is  advised 
in  cases  of  intestinal  disorder. 

Milk  also  undergoes  another  peculiar  fermentation,  by  which  it  is 
converted  into  a  thick,  ropy,  gelatinous  mixture. 

The  decomposition  of  the  milk-sugar  and  with  it  the  "curdling" 
may  be  prevented — 1,  by  chemical  treatment  with  alkaline  salts  or 
antiseptics  ;  2,  by  physical  treatment,  such  as  cooling  or  icing,  boil- 
ing and  aeration ;  3,  by  condensation  or  evaporation,  with  or  without 
the  addition  of  a  preservative  agent.  All  these  systems  of  preserva- 
tion, however,  are  subject  to  serious  disadvantages  because  they  either 
interfere  with  the  natural  constitution  and  properties  of  the  milk,  or 
because  they  serve  their  purpose  for  too  limited  a  time. 

The  addition  of  alkalies  such  as  lime-water,  sodium  carbonate  or 
bicarbonate,  does  not  prevent  the  lactic  fermentation,  but  prevents 
the  action  of  the  liberated  acid  on  the  casein  by  forming  a  lactate  of 
calcium  or  sodium. 

Milk  preservatives.  The  chemical  changes  in  milk  are  best  pre- 
vented by  cleanliness  and  preservation  at  a  low  temperature.  Various 
antiseptics,  such  as  salicylic  acid,  boric  acid,  formaldehyde,  benzoic 
acid,  etc.,  are  added  to  milk  with  the  view  of  preventing  decomposi- 
tion. While  the  small  quantities  used  appear  to  be  harmless,  yet 


MILK.  701 

there  can  be  no  doubt  that  the  continued  use  of  milk  containing  these 
preservatives  is  detrimental  to  health,  especially  in  the  case  of  human 
nurslings.  For  this  reason  many  countries,  States,  and  cities  prohibit 
legally  the  use  of  preservatives. 

Tests  for  preservatives  in  milk. 

Formaldehyde.  Float  a  mixture  of  10  c.c.  of  milk  and  10  c.c.  of  water  in  a 
test-tube,  on  concentrated  sulphuric  acid  made  pale  yellow  by  addition  of 
ferric  sulphate.  A  blue  to  violet  color  at  the  line  of  junction  shows  the  pres- 
ence of  formaldehyde.  Pure  milk  gives  a  greenish  color. 

Salicylic  acid.  Acidify  25  c.c.  of  milk  with  acetic  acid,  boil,  and  filter.  Ex- 
tract the  nitrate  with  an  equal  volume  of  ether.  Shake  the  ether  extract  with 
a  dilute  (straw-colored)  solution  of  ferric  chloride,  On  separating,  the  aqueous 
solution  shows  a  reddish-violet  color  when  salicylic  acid  is  present. 

Benzole  acid.  Proceed  as  in  the  foregoing  test,  but  shake  the  filtrate  with 
an  equal  volume  of  solution  of  hydrogen  dioxide  before  extracting  with  ether. 
By  this  treatment  benzoic  acid  is  converted  into  salicylic  acid,  which  is  then 
tested  for  by  ferric  chloride. 

Boric  acid  and  borax.  A  few  drops  of  the  filtrate  obtained  as  in  the  prece- 
ding test  are  mixed  with  a  drop  of  strong  hydrochloric  acid  and  a  drop  of  satu- 
rated alcoholic  solution  of  turmeric.  The  mixture  is  evaporated  to  dryness  on 
a  water-bath,  and  a  drop  of  ammonia  added  to  the  residue  when  cold.  A  dull- 
green  stain  shows  the  presence  of  boric  acid  or  borax. 

In  addition  to  the  test  for  chemical  preservatives,  commercial  milk 
is  now  examined  by  bacteriological  methods,  the  number  and,  if  pos^ 
sible,  the  character  of  the  organisms  being  determined.  By  extreme 
care  in  the  production  of  milk  it  is  possible  to  keep  the  count  lower 
than  30,000  per  cubic  centimeter  ("certified  milk").  A  cheaper 
method  of  producing  good  milk  is  by  heating  the  milk  for  a  certain 
time  to  a  temperature  below  the  boiling-point,  which  will  kill  all  the 
pathogenic  and  many  of  the  non-pathogenic  bacteria.  This  method 
is  commonly  called  "  pasteurization."  It  has  the  disadvantage  that 
the  digestibility  of  the  milk  is  lessened,  an  important  point  in  infant 
feeding. 

Experiment  94.  (Analysis  of  milk?)  As  the  proportion  of  fat  varies  at  dif- 
ferent periods  of  the  milking,  it  is  necessary  to  secure  a  sample  from  the  well- 
mixed  yield  of  milk.  a.  Determine  the  specific  gravity  of  milk,  cream,  and 
skimmed  milk  by  means  of  the  lactometer  (a  urinometer  answers  the  purpose). 

b.  Fat.  Determine  the  total  butter  fat  by  using  Babcock's  method,  which  is  as 
follows  :  Place  10  c.c.  of  milk  into  a  small,  specially  constructed  bottle  provided 
with  a  long,  slender,  graduated  neck ;  add  2  c.c.  of  a  mixture  of  ainyl  alcohol 
37,  methyl  alcohol  13,  and  hydrochloric  acid  50  parts;  then  fill  the  bottle  grad- 
ually with  sulphuric  acid.  Place  the  bottle  in  a  centrifugal  machine  and 
rapidly  revolve  for  three  minutes,  when  the  fat  is  forced  to  the  top  of  the 
mixture.  Add  enough  warm  water  to  float  the  separated  fat  into  the  neck, 
when  the  exact  percentage  can  be  read  on  the  scale.  A  special  form  of  bottle, 


702  PHYSIOLOGICAL   CHEMISTRY. 

arranged  for  small  quantities,  is  manufactured  for  the  examination  of  human 
milk. 

c.  Total  protein.     Separate  the  skimmed  milk  from  the  cream  of  the  sample 
under  observation.     Dilute  the  skimmed  milk  with  4  parts  of  water  and  with 
this  solution  fill  Esbach's  albuminometer  (see  Index)  to  the  mark   U,  add 
Esbach's  reagent  to  R,  and  allow  to  stand  24  hours.     Multiply  the  reading  by 
5;  the  result  gives  the  number  of  grammes  per  liter.     Skimmed  milk  is  used 
in  order  to  avoid  the  fat  which  would  be  carried  down  with  the  protein  if 
whole  milk  were  used. 

d.  Albumin  and  globulin.     Dilute  25  c.c.  of  milk  with  15  c.c.  of  water  in  a  50 
c.c.  flask,  heat  on  a  water-bath  to  38°  to  40°  C.  (100°  to  104°  F.),  and  add  very 
gradually  a  saturated  solution  of  potassium  alum  until  a  rapidly  subsiding 
coagulum  of  casein  forms.     Add  water  to  make  50  c.c.,  filter,  and  estimate  the 
simple  proteins  (albumin  and  globulin)  in  the  filtrate  by  means  of  the  albu- 
minometer, as  above,  multiplying  the  reading  on  the  instrument  by  2.  Another 
method  for  the  estimation  of  total  protein  or  of  the  simple  protein  depends  on 
the  accurate  determination  of  nitrogen  in  milk  or  in  milk  after  the  removal  of 
casein.     The  percentage  of  nitrogen  multiplied  by  6.25  gives  the  percentage  of 
protein.) 

e.  Determination  of  milk-sugar.     Lactose  can  be  estimated  by  titration  with 
Fehling's  solution ;  for  details  of  the  operation  see  chapter  on  Urine-analysis. 
A  second  method  depends  on  the  rotatory  power  of  lactose :  milk  is  freed  from 
protein  and  then  examined  by  the  polarimeter. 

/.  Determine  total  solids,  as  well  as  all  other  constituents,  by  following  the 
directions  given  above. 

Human  milk.  The  quantitative  differences  between  human  milk 
and  cows'  milk  have  been  shown  in  the  table  on  page  695 ;  they  con- 
sist chiefly  in  this,  that  human  milk  contains  only  about  one-half  the 
quantity  of  protein  and  of  inorganic  salts,  but  one-third  more  of 
lactose,  as  compared  with  cows'  milk.  In  addition,  it  may  be  said 
that  human  milk  is  richer  in  lecithin  ;  moreover,  the  proteins  of 
human  milk  differ  from  those  of  cows'  milk.  When  human  milk 
is  treated  with  acids  or  rennin,  casein  or  paracasein  is  formed  less 
readily  than  by  treating  cows'  milk  in  the  same  way.  The  precipi- 
tates show  marked  physical  differences  from  one  another.  Casein 
from  human  milk  is  easily  and  completely  soluble  in  gastric  juice, 
and  human  paracasein  is  precipitated  in  a  loose  and  flocculent  form, 
which  is  much  more  readily  digested  than  the  tough  and  more 
compact  masses  from  cows'  milk.  The  casein  of  human  milk  shows 
a  lower  percentage  of  carbon,  nitrogen,  and  phosphorus,  but  a  higher 
percentage  of  hydrogen,  sulphur,  and  oxygen,  than  casein  of  cows' 
milk.  Finally,  opalisin,  a  protein  rich  in  sulphur,  is  found  in  human 
milk  exclusively. 

Modified  milk,  used  for  infant  feeding,  is  cows'  milk,  the  composition  of 
which  has  been  changed  so  as  to  resemble  that  of  human  milk.  The  quantity 


URINE  AND  ITS  CONSTITUENTS.  703 

of  fat  is  increased  by  adding  cream,  or  by  removing  part  of  the  lower  layer 
from  milk  which  has  separated  into  two  layers  (top  milk).  This  mixture  is 
diluted  with  water  to  lower  the  percentage  of  protein ;  milk-sugar  and  lime- 
water  are  then  added  in  different  proportions,  according  to  the  quantity  desired. 
Although  the  difference  in  the  composition  of  human  and  cows'  milk  is  con- 
siderable, the  fuel  value  of  both  is  nearly  the  same,  about  315  calories  to  the 
pound  of  milk. 

58.    URINE  AND  ITS  CONSTITUENTS. 

Excretion  of  urine.  It  has  been  explained  in  a  former  chapter 
how  blood  absorbs  the  digested  food  as  chyle,  how  this  is  acted  upon 
by  the  atmospheric  oxygen  in  the  lungs,  and  how  this  arterial  blood, 
while  passing  through  the  system,  deposits  proteins  and  other  sub- 
stances, receiving  in  exchange  the  products  formed  by  the  oxidation 
of  the  various  tissues.  These  products  are  either  gases  (chiefly  car- 
bon dioxide),  liquids  (chiefly  water),  or  solids  held  in  solution  by  the 
water.  These  waste  materials  must  necessarily  be  eliminated  from 
the  system,  and  this  result  is  accomplished  principally  by  the  kidneys. 

The  urine  is  the  most  important  animal  excretion  ;  in  it  are  elimi- 
nated the  nitrogenous  waste  materials  as  well  as  most  of  the  water 
and  soluble  mineral  substances.  A  study  of  the  composition  of  the 
urine  will  give  important  information  regarding  metabolism,  the 
nature  of  the  chemical  processes  taking  place  within  the  body,  as 
also  of  the  condition  of  the  urinary  organs. 

General  properties.  Normal  human  urine,  when  in  a  fresh  state, 
is  a  clear,  transparent  aqueous  liquid,  of  a  lighter  or  deeper  amber 
color,  having  a  peculiar,  faintly  aromatic  odor,  a  bitter,  saline  taste, 
a  distinct  acid  reaction  on  blue  litmus-paper,  and  a  specific  gravity 
heavier  than  water  (averaging  about  1.020). 

In  urine,  shortly  after  cooling,  especially  if  it  be  concentrated,  a 
light,  cloudy  film  of  mucus  is  formed,  which  slowly  sinks  to  the 
bottom ;  the  acid  reaction  gradually  increases,  small  yellowish-red 

QUESTIONS. — Mention  the  five  principal  constituents  of  milk.  To  what 
group  of  compounds  does  casein  belong,  how  is  it  obtained,  and  what  are  its 
reactions?  Give  tests  for  milk-sugar,  and  state  how  it  may  be  distinguished 
from  grape-sugar.  What  physical  and  chemical  changes  does  milk  suffer  on 
standing?  Describe  the  processes  used  for  preserving  milk;  what  are  their 
advantages  and  disadvantages?  Give  approximately  the  quantities  of  the 
chief  components  of  cream,  skimmed  milk,  butter,  buttermilk,  curd,  whey,  and 
cheese ;  also  state  how  the  materials  are  obtained  from  milk.  Describe  the 
advantages  of  the  combined  use  of  the  lactometer  and  creamometer  in  testing 
milk.  What  are  the  differences  between  human  and  cows'  milk  ?  What  is 
paracasein?  Give  a  process  for  the  complete  quantitative  analysis  of  milk. 


704  PHYSIOLOGICAL   CHEMISTRY. 

crystals  of  acid  urates,  or  uric  acid,  are  deposited.  In  this  condition 
the  urine  may  often  continue  unchanged  for  several  weeks,  provided 
the  temperature  be  low.  If,  however,  the  temperature  be  above  the 
mean,  decomposition  speedily  takes  place.  The  urine  is  then  found 
to  be  covered  with  a  thin,  shining,  and  frequently  iridescent  mem- 
brane, fragments  of  which  sink  gradually  to  the  bottom.  The  urine 
then  becomes  turbid,  acquires  a  pale  color,  its  reaction  becomes  alka- 
line, and  it  begins  to  develop  a  nauseous  ammoniacal  odor,  due  to  the 
products  formed  by  the  decomposing  action  of  certain  microorganisms 
(chiefly  bacterium  ureaB  and  micrococcus  urea?)  upon  urea,  which  is 
converted  into  ammonium  carbonate  and  ammonium  carbamate.  The 
change  from  an  acid  to  an  alkaline  urine  causes  the  precipitation  of 
earthy  phosphates,  ammonium-magnesium  phosphate,  ammonium 
urate,  etc. 

Points  to  be  considered  in  the  analysis  of  urine.     They  are  : 

1.  Color,  odor,  general  appearance — whether  clear,  smoky,  cloudy, 
turbid,  etc. 

2.  Reaction — whether  acid,  neutral,  or  alkaline  to  test-paper. 

3.  Specific  gravity,  and  amount  for  twenty-four  hours. 

4.  Examination  of  sediments,  microscopically  and  chemically. 

5.  Chemical  examination   for  the   various  normal  and  abnormal 
constituents. 

Samples  of  urine  should  always  be  drawn  from  the  well-mixed  and 
exactly  measured  quantity  of  the  total  urine  discharged  in  twenty- 
four  hours. 

If  the  specimen  cannot  be  examined  promptly  it  should  be  pre- 
served in  a  stoppered  bottle  by  the  addition  of  a  very  small  amount 
of  chloroform  (3  to  5  c.c.  to  one  liter  of  urine). 

Color.  Normal  urine  is  generally  pale  yellow  or  reddish  yellow, 
but  it  may  be  as  colorless  as  water,  or  as  dark  brownish-black  as 
porter ;  a  reddish  and  smoky  tint  generally  indicates  the  presence  of 
blood,  and  a  brownish-green  suggests  the  presence  of  the  coloring- 
matter  of  bile. 

The  nature  of  the  normal  coloring-matters  of  urine  is  as  yet 
doubtful ;  the  existence  of  three  separate  pigments  has  been  demon- 
strated ;  they  have  been  named  urobilin,  urochrome,  and  uroerythrin, 
and,  most  likely,  are  products  of  the  decomposition  of  biliary  mat- 
ters. Numerous  other  substances,  such  as  indican,  occur  occasionally 
in  the  urine,  and  produce  various  colors,  especially  when  the  urine  is 
exposed  to  air  and  light,  or  when  acted  on  by  reagents. 


URINE  AND  ITS  CONSTITUENTS.  705 

Urochrome  is  the  yellowish  pigment  of  urine  ;  the  quantity  excreted, 
as  far  as  known,  has  no  clinical  significance.  It  is  probably  a  deriva- 
tive of  bilirubin. 

Uroerythrin  is  a  red  pigment,  and  causes  the  pink  color  often  seen 
in  urinary  sediments.  It  occurs  in  very  minute  quantity  in  normal 
urine,  and  is  increased  by  muscular  activity,  profuse  sweating,  ex- 
cessive eating,  alcohol  excess,  digestive  disturbance,  circulatory  dis- 
turbance of  the  liver,  malaria,  pneumonia,  and  many  other  patho- 
logical conditions.  Whenever  present  in  sufficient  quantity  to  give 
a  rose  color  to  the  sediment  or  to  the  precipitate  produced  by  adding 
barium  chloride  to  the  urine,  uroerythrin  is  excreted  in  increased 
quantity. 

Urobilin  y  a  reddish-brown  pigment,  occurs  normally  in  very  small 
quantity,  but  it  increases  considerably  whenever  there  is  great  de- 
struction of  haemoglobin  in  the  body  (internal  hemorrhage,  pernicious 
anemia,  poisoning  by  antipyrine),  in  cirrhosis  of  the  liver,  and  dur- 
ing high  fever.  When  present  in  excessive  quantity  urobilin  colors 
the  urine  a  dark  brownish-red,  and  the  foam  shows  a  yellow  or  yel- 
lowish-brown color. 

It  is  thought  to  be  usually  present  in  the  condition  of  a  chromogen, 
called  urobilinogen,  producing  the  pigment  urobilin  after  being  acted 
upon  by  light  or  by  an  acid. 

The  presence  of  urobilin  can  be  demonstrated  by  the  spectroscopic  exam- 
ination of  urine  to  which  a  small  amount  of  hydrochloric  acid  has  been  added. 
It  may  be  necessary  to  let  this  mixture  stand  a  short  time,  or  to  dilute  it,  or  to 
examine  the  amyl  alcohol  extract.  The  characteristic  spectrum  shows  a 
single  band  between  B.  and  F.  Urine  containing  urobilin  will  give  a  green 
fluorescence  on  the  addition  of  1  per  cent,  zinc  chloride,  if  it  has  been  previ- 
ously made  alkaline  with  ammonia  and  filtered. 

Abnormal  coloring-matters  are  chiefly  those  of  blood,  bile,  and  of 
certain  vegetables  and  drugs. 

Blood-pigment  is  usually  present  alone  as  methaemoglobin  in  hgemo- 
globinuria,  and  associated  with  the  red  blood-corpuscles  in  haematuria. 
Bile-pigment  will  be  discussed  later. 

The  ingestion  of  rhubarb,  senna,  or  santonin  produces  a  bright 
yellow  color  in  the  urine  which  becomes  red  on  the  addition  of  an 
alkali.  Methylene-blue  is  excreted  by  the  kidneys  and  colors  the 
urine  blue.  Urines  which  become  very  dark  on  standing  occur  after 
the  ingestion  of  phenol,  in  cases  of  melanotic  sarcoma  (melanogen), 
and  in  alkaptonuria,  an  unexplained  pathological  condition  in  which 

45 


706  PHYSIOLOGICAL   CHEMISTRY. 

homogentisic  acid  and  uroleucic  acid  (alkapton)  are  excreted  by  the 
kidneys. 

Odor.     The  normal  odor  of  fresh  urine  is  characteristic,  and  is 
sometimes  spoken  of  as  aromatic;  it  is  not  known  by  what  substance 
or  substances  this  odor  is  caused.     The  arnmoniacal  and  putrescent 
odor  which  urine  acquires  on  standing  is  due  to  the  products  of  de-' 
composition  formed,  chiefly  ammonia. 

A  number  of  substances  taken  internally  and  separated  by  the  kidneys  from 
the  blood,  cause  the  urine  to  assume  a  characteristic  odor ;  aromatic  substances 
especially  impart  such  odors;  oil  of  turpentine  gives  an  odor  reminding  of 
violets,  and  the  odor  of  cubebs,  copaiba,  asparagus,  garlic,  valerian,  and  other 
substances  is  promptly  transferred  to  the  urine  of  persons  using  these  drugs 
internally.  A  sweetish  smell  sometimes  attends  the  presence  of  large  quantities 
of  sugar  in  urine. 

Volume.  The  amount  of  urine  in  twenty-four  hours  varies  greatly 
under  physiological  conditions.  It  is  usually  between  900  and  1500  c.c. 
It  is  influenced  very  largely  by  the  amount  of  water  ingested,  by 
sweating,  by  diarrhoea,  etc.  It  is  decreased  in  acute  nephritis,  in- 
creased in  chronic  nephritis,  diabetes  mellitus,  and  diabetes  insipidus. 

Reaction.  This  is  generally  acid  in  healthy  urine  which  has  been 
recently  passed,  but  may  become  neutral  or  alkaline  within  a  short 
period,  by  decomposition  of  urea  and  formation  of  ammonium  car- 
bonate and  carbamate.  The  acid  reaction  of  urine  is  due  to  mono- 
sodium  ortho-phosphate,  NaH2PO4,  and  to  free  organic  acids.  These 
organic  acids  have  not  as  yet  been  identified. 

While  urine  shows  an  acid  reaction  generally,  it  may  have  a  neutral 
or  even  alkaline  reaction.  In  many  cases  this  alkaline  reaction  points 
to  decomposition  of  urea  in  the  bladder,  but  it  may  be  due  also  to  the 
elimination  of  alkali  carbonates,  derived  from  food  taken  or  drugs 
administered. 

Thus,  the  alkali  tartrates,  citrates,  acetates,  etc.,  have  (after  diges- 
tion) a  tendency  to  neutralize  the  urine,  and  an  excess  of  them  is 
eliminated  as  carbonate. 

To  distinguish  between  the  harmless  alkaline  reaction  caused  by 
fixed  alkalies  and  the  alkaline  reaction  produced  by  decomposition  of 
urea,  a  piece  of  red  litmus-paper  may  be  used.  If  this,  after  having 
been  moistened  with  the  urine,  remains  blue  on  drying  (by  warming 
gently)  the  reaction  is  due  to  the  fixed  alkalies  ;  if  the  red  color 
reappears,  the  alkaline  is  due  to  ammonia  compounds. 

This  distinction  possesses  no  importance  in  urine  which  has  become 
alkaline  on  standing. 


URINE  AND  ITS  CONSTITUENTS. 


707 


FIG.  73. 


Urine  sometimes  is  amphoteric  in  its  reaction,  i.  e.,  it  colors  red  litmus-paper 
faintly  blue,  and  blue  litmus-paper  slightly  red.  This  condition  is  caused  most 
likely  by  the  simultaneous  presence  of  monosodium  orthophosphate,  NaH2PO4, 
which  has  an  acid,  and  of  disodium  orthophosphate,  NaH2PO4,  which  has  an 
alkaline,  reaction. 

The  acidity  of  the  urine  is  best  determined  in  the  following  manner 
(Folin) :  25  c.c.  of  urine  are  shaken  in  a  flask  with  15  to  20  grammes 
of  powdered  potassium  oxalate,  1  to  2 
drops  of  phenolphthalein  (J  per  cent, 
solution  in  alcohol)  are  added,  and  the 
mixture  titrated  at  once  with  •£$  sodium 
hydroxide.  The  end-reaction  is  the  for- 
mation of  a  distinct  pink  color.  The 
acidity  of  the  urine  is  usually  expressed 
in  terms  of  -^  acid  or  alkali  for  twenty- 
four  hours. 

The  oxalate  is  added  to  precipitate 
calcium,  and  thus  avoid  the  deposition 
of  calcium  phosphate  as  the  mixture 
becomes  alkaline.  It  also  reduces  the 
error  due  to  ammonium. 


Specific  gravity.  The  normal  spe- 
cific gravity  of  an  average  amount  of 
1500  c.c.  of  urine  passed  in  twenty-four 
hours  is  about  1.020,  but  it  varies,  even 
in  health,  from  1.012  to  1.030  or  more. 
A  specific  gravity  above  1.030  may 
indicate  the  presence  of  sugar,  larger 
quantities  of  which  may  cause  the  spe- 
cific gravity  to  rise  to  1.050.  Albumi- 
nous urine  is  frequently  of  low  specific 
gravity,  1.010  to  1.012,  especially  in 
chronic  nephritis. 

It  should  be  remembered  that  the 
specific  gravity  of  urine  considered 
separately  from  the  quantity  of  urine  passed  in  twenty-four  hours  is 
of  no  value,  and  that  in  some  diseases  (for  instance  in  acute  nephritis 
with  albuminuria)  the  specific  gravity  of  albuminous  urine  may  be  as 
high  as  1.030,  while  a  diabetic  urine  may  have  a  specific  gravity  of 
1.025,  or  less,  in  consequence  of  a  large  volume  passed. 

The  determination  of  the  specific  gravity  of  urine  is  generally  accom- 


Urinometer. 


708  PHYSIOLOGICAL   CHEMISTRY. 

plished  by  the  urinometer,  which  is  a  small  hydrometer  indicating  spe- 
cific gravity  from  zero  (or  1000)  to  60  (or  1060).  (See  Fig.  73.)  As 
the  temperature  influences  the  density  of  liquids,  a  urinometer  can 
only  give  correct  results  at  a  certain  degree  of  temperature,  which  is 
generally  marked  upon  the  instrument. 

Composition.  Urine  is  chiefly  an  aqueous  solution  of  urea  and 
inorganic  salts,  containing,  however,  always  some  uric  acid,  coloring-, 
and  other  organic  matters. 

Urine  also  contains  gaseous  constituents,  amounting  to  about  16 
per  cent,  by  volume  ;  these  gases  are  chiefly  carbon  dioxide  (88  per 
cent.)  and  nitrogen  (11  per  cent.),  with  very  little  oxygen  (1  per  cent.). 

The  quantity  of  urine  passed  in  a  day  also  varies  widely,  an  adult 
discharging  from  500  to  2300  c.c.  in  twenty-four  hours ;  a  normal 
average  quantity  is  about  1000  to  1500  c.c.  (about  36  to  54  ounces). 
The  quantity  of  total  solids  contained  in  this  urine  varies  from  55  to  60 
grammes  (840  to  920  grains),  and  about  one-half  of  this  quantity  is  urea. 

As  many  of  the  .so-called  pathological  constituents  of  urine  are 
actually  present  in  minute  quantities  in  normal  urine,  it  is  difficult  to 
make  an  absolute  distinction  between  physiological  and  pathological 
constituents.  Below  is  given  a  working  classification  of  the  more 
important  constituents,  regarding  as  normal  those  whose  presence  may 
readily  be  shown  by  clinical  tests.  Accordingly,  indican,  for  ex- 
ample, is  placed  with  the  normal  bodies,  while  acetone  is  placed  with 
the  pathological  substances,  though  both  are  normally  present  in 
small  amounts. 

Normal  constituents. 
Urea. 
Ammonia. 


Nitrogen  as 


Creatinine. 


Uric  acid.        (  Xanthine  bases. 
Other  bodies  <  Allantoin. 

(  Hippuric  acid. 
Chlorine  as  chlorides. 

Phosphorus  as  phosphoric  acid.  ( ( 1 )  Inorganic  (K,  Na,  etc.). 

Sulphur  as    {  Neutral  sulPlmr-  (2)  Organic  (ethereal). 

(Oxidized  sulphur  =  sulphates:  \        Indole  (indican). 
Sodium,         }  Skatole. 

Potassium,     I  .  .  [       Phenol. 

Calcium,  Combined  with  acids. 

Magnesium,  I 
Oxalic  acid. 
Pigments. 
Enzvmes. 


URINE  AND  ITS  CONSTITUENTS.  709 


Pathological  constituents. 

f  Serum  albumin. 
Serum  globulin. 

Albumose  (proteose). 
Proteins : 

Peptone. 

Bence-Jones  albumin. 
.  Haemoglobin. 


Carbohydrates : 


Glycuronic  acid. 


Glucose  (dextrose). 

Levulose. 

Maltose. 

Lactose. 

Pentose. 


f  /3-oxy-butyric  acid. 
Acetone  bodies  -j  Diacetic  acid. 
I  Acetone. 

Biliary  acids,  biliary  pigments. 

Melanin. 

Alkapton. 

Unknown  body  or  bodies  giving  the  Ehrlich  diazo-reaction. 

Determination  of  total  solids.  An  approximate  determination 
of  total  solids  may  be  deduced  from  the  specific  gravity  of  the  urine, 
as  it  has  been  found  that  the  last  two  figures  of  the  specific  gravity 
of  urine,  multiplied  by  2.2,  correspond  to  the  number  of  grammes  in 
1000  c.c.  of  urine.  If,  for  instance,  1450  c.c.  of  urine,  of  a  specific 
gravity  of  1 .018,  have  been  discharged  in  twenty-four  hours,  then  the 
quantity  of  total  solids  in  1000  c.c.  will  be  18  X  2.2,  or  39.6  grammes  ; 
and  in  1450  c.c.,  57.42  grammes. 

A  more  exact  method  of  determining  the  total  solids  in  urine  is  the  evapora- 
tion of  about  10  c.c.  in  a  weighed  platinum  dish  over  a  water-bath  (or,  better, 
under  the  receiver  of  an  air-pump  over  sulphuric  acid),  until  it  is  found  that  no 
more  loss  in  weight  ensues  on  continued  exposure  of  the  dish  in  the  drying 
apparatus.  By  now  reweighing  the  dish,  plus  contents,  and  deducting  from 
the  weight  that  of  the  empty  dish,  the  weight  of  total  solids  is  found.  This 
determination  has  practically  no  clinical  value. 

Determination  of  inorganic  constituents.  The  platinum  dish 
containing  the  known  quantity  of  total  solids  is  exposed  to  the  action 
of  a  non-luminous  flame,  and  the  heat  continued  until  all  organic 
matter  has  been  destroyed  and  expelled.  By  reweighing  now,  and 
deducting  the  weight  of  the  platinum  dish,  plus  ash,  from  the  weight 


710  PHYSIOLOGICAL   CHEMISTRY. 

of  the  dish,  plus  total  solids,  the  quantity  of  total  organic  matter  is 
determined ;  and  by  deducting  weight  of  dish  from  weight  of  dish 
plus  ash,  the  total  quantity  of  inorganic  matter  is  found. 

The  analysis  of  the  ash  is  effected  by  the  methods  given  in  con- 
nection with  the  consideration  of  the  various  acid  and  basic  constitu- 
ents themselves.  Chlorine  is  determined  by  precipitating  the  solution 
of  the  ash  in  nitric  acid  with  silver  nitrate,  sulphuric  acid  by  barium 
chloride,  phosphoric  acid  by  ammonium  molybdate,  calcium  by  ammo- 
nium oxalate,  potassium  by  chloroplatinic  acid,  iron  by  potassium 
ferrocyanide,  etc. 

As  the  methods  outlined  above  are  too  involved  for  clinical  wrork, 
no  details  are  given.  Modern  methods  for  quantitative  urinary  analy- 
sis are  practically  all  volumetric,  and  will  be  described  for  the  various 
constituents  of  the  urine. 

Nitrogen  in  the  urine.  The  nitrogen  in  the  urine  is  derived  di- 
rectly from  protein  metabolized.  As  only  a  small  part  of  the  nitro- 
gen is  excreted  in  the  feces  and  sweat,  the  estimation  of  the  urinary 
nitrogen  is  the  most  commonly  used  procedure  for  determining  the 
amount  of  protein  broken  down  in  the  body.  The  total  nitrogen 
varies  from  10  to  16  grammes  a  day,  and,  as  indicated  above,  varies  with 
the  protein  metabolism.  Thus  it  is  increased  with  a  heavy  meat  diet, 
with  fever,  in  diabetes,  etc.  The  approximate  distribution  of  the 
urinary  nitrogen  is : 

Urea 85  per  cent. 

Ammonia 5-6  per  cent. 

Creatinine 4  per  cent. 

Uric  acid 0.5-1  per  cent. 

Other  nitrogen 3-5  per  cent,  (hippuric  acid,  xanthine 

bases,  etc.). 

The  estimation  of  nitrogen  alone  has  little  clinical  value,  but  it  is 
frequently  done  in  order  to  find  the  percentage  of  ammonia,  which  is 
very  valuable.  The  method  used  is  the  customary  Kjeldahl  method 
(p.  445),  using  the  Gunning  mixture  of  sulphuric  acid,  sodium  sul- 
phate, and  copper  sulphate. 

Normal  nitrogenous  constituents  of  urine.  The  more  important  are 
urea,  uric  acid,  ammonia,  creatiniiie  (creatine).  Less  important  are 
the  xanthine  bases,  hippuric  acid,  etc. 

Urea,  Carbamide,  CO(NH2)2,  or  COli<^  *.  Urea,  the  most  im- 
portant constituent  of  urine,  is  the  chief  nitrogenous  end-product  of 
the  metabolism  of  proteins  in  the  body,  and  carries  off  by  far  the 


URINE  AND  ITS  CONSTITUENTS.  711 

largest  quantity  of  all  nitrogen  ingested  with  the  food.  From  85  to 
86  per  cent,  of  the  total  nitrogen  of  the  urine  is  found  in  urea,  the 
formation  of  which  in  the  liver  has  been  considered  heretofore.  Urea 
has  never  yet  been  found  as  a  product  of  vegetable  life,  but  is  found 
as  a  normal  constituent  of  the  urine  of  the  mammalia,  and  in  smaller 
quantity  in  the  excrement  of  birds,  fishes,  and  some  reptiles.  It 
occurs  in  small  quantities  also  in  blood,  muscular  tissue,  lymph,  per- 
spiration, and  many  other  animal  fluids.  Pathologically  urea  may 
appear  in  all  fluids  and  tissues. 

When  pure,  urea  crystallizes  from  an  aqueous  solution  in  colorless 
prisms  ;  it  is  colorless,  and  has  a  cooling,  bitter  taste  ;  it  easily  dis- 
solves in  water,  the  solution  having  a  neutral  reaction  ;  it  fuses  when 
heated  at  130°  C.  (266°  F.),  but  decomposes  at  a  higher  temperature, 
giving  off  ammonia  gas  and  water,  while  a  number  of  other  sub- 
stances are  formed  at  the  same  time.  A  pure  solution  of  urea  does 
not  decompose  at  ordinary  temperature,  but  on  boiling,  and  especially 
under  pressure,  it  takes  up  water,  and  is  decomposed  into  ammonia 
and  carbon  dioxide,  or  into  ammonium  carbonate  : 

CO(NH2)2  4-  2H20  =  C02  +  2NH3  +  H2O  =  (NH4)2CO3. 

The  same  decomposition  takes  place  in  urine  under  the  influence 
of  a  bacterial  enzyme,  if  the  temperature  be  not  too  low. 

A  solution  of  urea  is  decomposed  by  the  action  of  chlorine  or 
bromine  with  generation  of  hydrochloric  (or  hydrobromic)  acid,  car- 
bon dioxide,  and  nitrogen  : 

CO(NH2)2  +  6C1  +  H20  =  6HC1  +  CO2  +  2N. 

Alkali  hypochlorites  or  hypobromites  cause  a  similar  decomposi- 
tion, upon  which  is  based  the  quantitative  estimation  of  urea. 

Urea  forms  with  acids  definite  salts,  and  with  certain  oxides  and 
salts  definite  compounds. 

Urea  is  formed  artificially  by  numerous  decompositions,  as,  for  instance  : 

a.  By  a  process  similar  to  the  one  taking  place  in  the  animal  system,  viz.} 
by  limited  oxidation  of  albuminous  substances  by  potassium  permanganate. 

b.  By  oxidation  of  uric  acid  in  the  presence  of  water  : 


403  +  H20  +  O  =  CO(NH2)2  + 
Uric  acid.  Urea.  Alloxan. 

c.  By  the  action  of  caustic  alkalies  upon  creatine  : 

C4H9N,O2    +    H2O    =    CO(NH2)2     +     C3H7NO2. 
Creatine.  Urea.  Sarcosine. 

d.  By  the  molecular  transformation  of  ammonium  cyanate,  which  tahea 
place  when  its  solution  is  evaporated  and  allowed  to  crystallize  : 

NH4.CXO    =    CO(NH2)2. 


712  PHYSIOLOGICAL   CHEMISTRY. 

e.  By  the  action  of  carbonyl  chloride,  COC1.2,  on  ammonia : 
COC12     +     2NH3    =   :    2HC1    +     CO(NH2)2. 
/.  By  the  action  of  ammonia  on  ethyl  carbonate  : 

(C2H5)2C03     +     2NH3  2C2H5OH    +     CO(NH2)2. 

Urea  may  be  obtained  from  urine  by  evaporating  it  to  the  consist- 
ence of  a  syrup  and  mixing  the  cooled  residue  with  an  equal  volume 
of  nitric  acid,  when  crystals  of  urea  nitrate,  CO(NH2)2.HNO3,  form, 
which  may  be  decomposed  by  barium  carbonate  into  urea  and  barium 
nitrate : 

2[CO(NH2)2.HNO3]  +  BaCO3  =  2CO(NH2)2  +  Ba(NO3)2  +  CO2  +  H2O. 

Experiment  95.  Evaporate  about  200  c.c.  of  urine  to  a  syrupy  consistence, 
allow  to  cool,  place  the  vessel  containing  the  syrup  in  ice  and  add  slowly  with 
stirring  a  volume  of  nitric  acid  equal  to  that  of  the  evaporated  urine.  Set 
aside  for  twenty-four  hours,  collect  the  crystalline  mass  of  urea  nitrate  on  a 
filter,  wash  with  very  little  cold  water,  allow  to  drain  well,  dissolve  in  hot 
water,  and,  while  the  solution  boils  gently,  add  small  quantities  of  potassium 
permanganate  until  the  solution  is  colorless.  To  the  hot  solution  add  freshly 
precipitated  barium  carbonate  as  long  as  carbon  dioxide  escapes.  Filter  and 
evaporate  the  solution  to  dryness  over  a  water-bath ;  boil  the  mass  with  alco- 
hol, which  dissolves  the  urea,  but  does  not  act  on  the  barium  nitrate.  Allow 
the  urea  to  crystallize  from  the  alcoholic  solution. 

Reactions  of  urea.  There  are  no  very  characteristic  reactions  by 
which  urea  can  be  well  recognized.  From  organic  mixtures  it  is 
separated  by  digesting  them  with  from  3  to  4  volumes  of  alcohol  in 
the  cold  ;  the  filtered  liquid  is  evaporated  to  dryness  and  extracted 
with  alcohol,  which  again  is  evaporated.  The  dry  residue  may  be 
tested  for  urea  as  follows  : 

1.  Dissolved  in  a  few  drops  of  water,  the  addition  of  an  equal 
quantity  of  colorless  nitric  acid  causes  the  formation  of  white,  shin- 
ing, crystalline  plates  or  prisms  of  urea  nitrate. 

2.  If  a  strong  solution  of  oxalic  acid  is  added,  instead  of  nitric 
acid,  rhombic  plates  of  urea  oxalate  form. 

3.  The  residue  (or  urea)  heated  in  a  test-tube  to  about  160°  C. 
(320°  F.)  until  no  more  vapors  of  ammonia  are  evolved,  leaves  a 
substance  termed  biuret,  C2H6N3O2,  which,  upon  the  addition  of  a  few 
drops  of  potassium  hydroxide  solution  and  a  drop  of  cupric  sulphate 
solution,  causes  the  solution  of  the  cupric  hydroxide  with  a  reddish- 
violet  color. 

Determination  of  urea.  The  amount  of  urea  in  twenty-four  hours 
is  normally  from  25  to  35  grammes.  The  greater  part  of  it  is  derived 


URINE  AND  ITS  CONSTITUENTS.  713 

from  the  exogenous  protein  metabolism,  and  the  total  quantity  is 
thereby  largely  affected  by  the  diet.  It  is  increased  by  a  meat  diet, 
as  is  the  total  nitrogen  output ;  it  is  decreased  in  fever.  In  disease 
of  the  two  organs  most  concerned  with  urea  elimination,  the  liver 
(formation)  and  the  kidney  (excretion),  it  is  usually,  though  not  always, 
decreased. 

The  quantitative  estimation  of  urea  in  urine  may  be  effected  by 
various  methods,  of  which  but  one  will  be  mentioned,  because  it  re- 
quires less  time  and  less  skill  in  manipulation  than  most  other 
methods.  This  determination  is  based  upon  the  fact  that  urea  is 
decomposed  by  alkali  hypobromites  into  carbon  dioxide,  water,  and 
nitrogen : 

CO(NH2)2  +  3(NaBiO)  =  SNaBr  +  CO,  +  2H2O  +  2N. 

The  liberated  nitrogen  is  collected,  and  from  its  volume  the  weight 
of  the  urea  is  calculated.  The  carbon  dioxide  is  absorbed  by  the 
excess  of  alkali  present.  The  hypobromite  solution  must  be  prepared 
freshly  by  making  the  following  mixture  of: 

(a)  1  volume  of  a  solution  containing  bromine,  125  grammes ; 
sodium  bromide,  125  grammes;  water,  1  liter. 

(6)  1  volume  of  22.5  per  cent,  sodium  hydroxide  solution. 

(c)  3  volumes  of  water. 

2NaOH     +     2Br    =    NaBr     +     NaOBr     -t    H2O. 

Of  the  many  instruments  recommended  for  the  determination  of  urea,  the 
latest  modification  of  Doremus'  apparatus  (Fig.  74)  is  most  convenient.  The 
operation  is  carried  out  thus :  Some  urine  is  poured  into  B,  while  the  stopcock 
C  is  closed  and  then  opened  for  a  moment  so  as  to  fill  its  lumen.  After  having 
washed  the  tube  A  with  water,  it  is  filled  with  the  hypobromite  solution.  From 
the  tube  B,  previously  filled  with  urine.  1  c.c.  (or  less  if  much  urea  is  present) 
is  allowed  to  mix  with  the  hypobromite  solution,  and  after  the  reaction  is  com- 
pleted the  reading  is  taken.  The  degrees  marked  upon  the  tube  A  indicate 
directly  the  number  of  grammes  of  urea  contained  in  -the  quantity  of  urine 
employed. 

Albumin  must  be  removed,  if  present,  and  for  careful  work  the  specimen 
must  contain  not  more  than  1  per  cent,  of  urea,  which  can  be  readily  accom- 
plished by  diluting  a  second  specimen. 

For  careful  work  this  method  is  not  sufficiently  accurate,  and  the  Folin 
method  should  be  used. 

Experiment  96.     Determine  urea  in  urine  by  the  above-described  methods. 

Ammonia  in  the  urine.  Ammonia  is  normally  present  in  the 
urine  in  small  amount,  representing  about  5  or  6  per  cent,  of  the  total 
nitrogen.  The  amount  seems  dependent  upon  two  factors  :  the  ability 
of  the  organism  to  convert  the  waste  nitrogen  from  the  proteins  into 


714 


PHYSIOLOGICAL   CHEMISTRY. 


urea,  and  the  necessity  of  neutralizing  the  acid  radicals  of  the  urine 
which  are  normally  in  excess  of  the  basic  radicals.  Accordingly, 
the  urinary  ammonia  is  increased  when  the  urea-forming  apparatus  is 
deficient — •/.  e.,  in  certain  disease  of  the  liver.  It  is  likewise  increased 
in  the  presence  of  an  abnormal  excess  of  acid — e.  g.,  the  acidosis  of 
diabetes  and  of  the  pernicious  type  of  vomiting  in  pregnancy.  As 
the  absolute  amount  of  ammonia  in  the  urine  is  greatly  modified  by 

FIG.  74. 


Doremus'  ureometer. 


the  amount  of  total  nitrogen,  it  is  necessary  to  estimate  the  amounts 
of  each  in  order  to  obtain  the  important  point — the  ammonia  fraction 
of  the  total  nitrogen. 

Estimation  of  ammonia  in  the  urine.  The  ammonia  in  a  measured 
amount  of  urine  is  set  free  by  the  addition  of  sodium  carbonate.  By 
means  of  a  suitable  closed  system  of  apparatus  and  an  ordinary  suc- 
tion pump  a  current  of  air  is  carried  through  this  mixture  and 
allowed  to  bubble  up  through  a  measured  amount  of  £  sulphuric  acid. 
At  the  end  of  an  hour  and  a  half  all  of  the  ammonia  will  have  been 


VRINE  AND  ITS  CONSTITUENTS.  715 

carried  over,  and  the  excess  of  acid  is  titrated  with  ~  sodium  hydroxide 
with  alizarin  as  an  indicator. 

Creatinine  is  normally  present  in  urine  to  the  amount  of  1  or  2 
grammes  in  twenty-four  hours.  It  is  believed  to  be  derived  from  the 
creatine  of  muscle,  and  mainly  from  the  body  muscle,  not  the  food. 
Its  significance  is  still  much  disputed,  as  an  accurate  method  of  esti- 
mation has  been  only  comparatively  recently  devised  (Folin,  1905). 
Creatine  is  not  normally  present  in  urine. 

Creatinine  is  best  recognized  in  the  urine  by  removing  the  phos- 
phates and  coloring-matter  by  milk  of  lime,  concentrating  the  filtrate 
by  evaporation,  and  applying  the  tests  mentioned  before.  As  crea- 
tinine is  a  reducing  agent,  its  presence  in  urine  will  influence  the  tests 
for  sugar  based  on  its  deoxidizing  power. 

Make  tests  2  and  3  of  Experiment  77,  to  show  the  presence  of  creatinine  in 
urine. 

NH— CO 

Uric    acid,    H2C5H2N4O3.       2.6.8.  Oxypurine,     CO     C-NH^ 

,co. 

NH— C— NHX 

Uric  acid  is  found  in  small  quantities  in  human  urine,  chiefly  in  com- 
bination with  sodium,  potassium,  and  ammonium,  but  also  with  cal- 
cium and  magnesium.  In  larger  proportions,  uric  acid  is  found  in 
the  excrement  of  birds,  mollusks,  insects,  and  chiefly  of  serpents,  the 
solid  urine  of  the  latter  consisting  almost  entirely  of  uric  acid  and 
urates.  It  is  also  found  in  Peruvian  guano.  The  proportion  of  uric 
acid  to  urea  in  human  urine  is  normally  between  1  :  50  and  1  :  70. 
The  normal  amount  for  twenty-four  hours  is  about  0.7  gramme. 

Pure  uric  acid  is  a  white,  crystalline,  tasteless,  and  odorless  sub- 
stance, almost  insoluble  in  water,  requiring  1900  parts  of  boiling  and 
15,000  parts  of  cold  water  for  its  solution;  it  is  also  insoluble,  or 
nearly  so,  in  alcohol  and  ether.  The  great  insolubility  of  uric  acid 
causes  its  separation  in  the  solid  state,  both  in  the  bladder  and  in  the 
tissues. 

It  is  believed  that  uric  acid  is  derived  by  oxidation  from  the  purine 
bodies  of  the  nucleins,  and  is  increased  when  there  is  an  increase  in 
nuclein  metabolism.  That  coming  from  the  tissue  nucleins  is  termed 
"  endogenous "  uric  acid;  that  from  the  food  nucleins  is  termed 
"  exogenous."  While  uric  acid  is  formed  synthetically  in  the  liver 
of  birds,  such  a  synthesis  has  not  been  proved  for  man.  It  seems 
probable  that  most  of  the  waste  nitrogen  in  birds,  as  in  man,  is  con- 
verted into  urea ;  but  is  further  changed  to  uric  acid  for  excretion. 


716  PHYSIOLOGICAL   CHEMISTRY. 

The  exogenous  uric  acid  is  increased  on  a  diet  rich  in  nucleopro- 
teins  (sweetbreads) ;  the  endogenous  uric  acid,  being  derived  mainly 
from  the  muscles  and  the  leucocytes,  is  increased  after  exercise,  in 
leukaemia,  etc. 

Experiment  97.  (Preparation  of  uric  acid.)  Add  100  c.c.  of  hydrochloric 
acid  to  1  liter  of  urine  and  set  aside  for  a  day.  Collect  the  highly  colored 
crystals  of  uric  acid,  wash  with  water,  transfer  them  to  a  beaker  with  a  little 
water,  heat,  and  add  enough  sodium  hydroxide  to  dissolve  the  crystals.  Decol- 
orize the  solution  of  sodium  urate  with  boneblack,  filter  while  hot,  acidify  with 
hydrochloric  acid,  and  allow  to  crystallize.  Examine  the  crystals  microscop- 
ically and  chemically. 

Tests  for  uric  acid. 

1.  Murexide  test.  Place  a  few  fragments  of  uric  acid  in  a  porcelain 
dish,  add  a  drop  of  nitric  acid,  and  carefully  evaporate  over  a  flame. 
To  the  dry  residue  add  a  drop  of  ammonia- water,  which  produces  a 
beautiful  purplish-red  color.  (Plate  VIII.,  4.) 

To  distinguish  from  xanthine  and  guanine,  add  a  drop  of  caustic 
soda,  when  the  red  changes  to  a  deep  blue  color.  Moisten  with  water 
and  evaporate  to  dryness,  when  the  color  disappears.  With  xanthine 
or  guanine  the  color  persists. 

For  the  following  tests  use  solution  of  sodium  urate  prepared  by  dissolving 
uric  acid  in  warm  water  with  the  aid  of  sodium  carbonate. 

2.  Schif's  reaction.     Place  a  drop  of  the  solution  on  a  piece  of 
filter-paper  previously  moistened  with  silver  nitrate.     A  dark  stain 
is  formed,  due  to  the  reduction  of  the  silver  salt. 

3.  Boil  with  Fehling's  solution.    A  gray  precipitate  is  formed  when 
uric  acid,  a  reddish  precipitate  when  the  copper  solution,  is  in  excess. 
(The  reaction  shows  the  necessity  of  exercising  judgment  in  drawing 
conclusions  when  testing   for  sugar  in  urine  with  reducing  agents.) 

4.  Add  magnesia-mixture  and  then  silver  nitrate.  Uric  acid  is 
precipitated  as  a  gelatinous  magnesia-silver  salt.  (This  reaction  may 
be  used  to  precipitate  uric  acid  from  urine,  especially  in  those  cases 
in  which  hydrochloric  acid  fails  to  precipitate  the  acid.) 

Quantitative  estimation  of  uric  acid.  Of  the  many  methods  de- 
scribed for  this  purpose,  the  one  which  is  based  on  the  separation  of 
uric  acid  and  its  subsequent  titration  with  potassium  permanganate 
is  best  adapted  for  the  needs  of  the  physician.  It  is  carried  out 
thus : 

Uric  acid  is  precipitated  by  ammonium  sulphate  as  ammonium 
urate,  which  is  filtered  off  and  isolated.  On  the  addition  of  sul- 


URINE  AND  ITS  CONSTITUENTS.  717 

phuric  acid,  uric  acid  is  set  free  and  the  amount  is  titrated  with  ^ 
potassium  permanganate  solution. 
Reagents  used  : 

1.  Ammonium   sulphate,   500;    uranium   acetate,   5;    acetic   acid 
(10  per  cent.),  60  ;  water,  650. 

2.  Ammonium  sulphate,  10  per  cent,  solution. 

3.  f-Q  potassium  permanganate.     . 

To  100  c.c.  of  urine  add  25  c.c.  of  reagent  1  ;  let  stand  until  the 
precipitate  has  settled  (five  to  ten  minutes)  and  filter  through  two 
folded  filter-papers.  To  100  c.c.  of  filtrate  add  5  c.c.  of  concentrated 
ammonia  water  and  let  stand  for  twenty-four  hours.  Pour  off  the 
supernatant  fluid  through  a  filter  and  collect  on  it  the  precipitate  of 
ammonium  urate  with  the  aid  of  some  10  per  cent,  ammonium  sul- 
phate ;  wash  with  the  same  solution  for  a  short  time.  Open  the 
filter  and  collect  the  precipitate  in  a  beaker  with  about  100  c.c.  of 
water.  Add  15  c.c.  of  concentrated  sulphuric  acid,  which  will  dis- 
solve it.  Titrate  at  once  (while  hot)  with  potassium  permanganate 
-/-$.  The  end-reaction  is  the  first  trace  of  rose  color  present  through- 
out the  beaker  after  the  addition  of  two  drops  of  the  reagent  in 
excess. 

Calculation  :  As  there  is  used  in  the  titration  only  £  of  the  original 
amount  of  urine  (taking  100  c.c.  of  the  first  filtrate,  not  the  whole 
125  c.c.),  J  of  the  result  of  the  titration  is  the  amount  of  permanga- 
nate which  would  correspond  to  100  c.c.  of  urine.  Each  cubic  centi- 
meter of  the  permanganate  corresponds  to  0.00375  gramme  of  uric 
acid  from  which  it  is  simple  to  calculate  the  amount  of  uric  acid 
present  in  the  urine. 

Correction  :  As  ammonium  urate  dissolves  to  the  extent  of  0.003 
gramme  in  100  c.c.,  this  amount  must  be  added  for  every  100  c.c.  of 
urine. 

Xanthine  bodies.  The  xanthine  bodies  are  normally  present  in 
urine  in  small  amount.  Those  present  in  largest  amount  are  para- 
xanthine,  heteroxanthine,  and  methylxanthine,  which  arise  from  the 
similar  bodies,  caffeine,  theobromine,  and  theophylline,  in  the  food. 
Otherwise  the  origin  and  significance  of  the  purine  bodies  are  thought 
to  be  the  same  as  those  of  uric  acid. 

Allantoin  (glyoxyldiureide),  C4H6N4O3,  is  normally  present  in 
minute  amounts  in  adults,  more  abundantly  in  the  newborn.  While 
it  will  reduce  Fehling's  solution,  the  amount  present  is  never  suf- 
ficient to  give  a  positive  test. 

Hippuric    acid,  CgHgNOj  (Benzoyl-glycocoll,  Benzoyl-amino-acetic 


718  PHYSIOLOGICAL   CHEMISTRY. 

acid),  is  a  normal  constituent  of  human  urine,  but  is  found  in  much 
larger  quantities  in  the  urine  of  herbivora.  Its  constitution  is 
CH2.NH— CO2H, 

|  and  is  the  result  of  the  combination  of  glycocoll 

C6H5CO 

and  benzoic  acid.  This  synthesis  occurs  in  the  kidney.  Hay,  and 
especially  aromatic  herbs,  contain  benzoic  acid,  or  compounds  having 
a  similar  composition,  and  a  portion  of  these  compounds  is  eliminated 
in  hippuric  acid.  Administration  of  benzoic  acid  increases  the  amount 
of  hippuric  acid  in  urine. 

When  pure,  hippuric  acid  crystallizes  in  transparent,  colorless, 
odorless  prisms,  which  have  a  bitter  taste,  and  are  sparingly  soluble 
in  water. 

Experiment  98.  (Preparation  of  hippuric  acid.}  To  400  c.c.  of  horse's  urine 
add  some  milk  of  lime,  heat,  filter,  evaporate  the  filtrate  to  a  small  volume, 
and  acidify  with  hydrochloric  acid.  The  calcium  hippurate  which  had  been 
formed  is  decomposed  and  the  liberated  hippuric  acid  separates  either  at  once 
or  on  standing.  If  too  highly  colored,  dissolve  crystals  in  hot  water  contain- 
ing some  ammonia,  decolorize  solution  with  boneblack,  filter,  acidify  with 
hydrochloric  acid,  and  recrystallize.  Examine  crystals  microscopically  and 
chemically. 

Tests  for  hippuric  acid. 

1.  Heat  in  a  dry  test-tube :  a  sublimate  of  benzoic  acid  is  formed 
and  the  odor  of  hydrocyanic  acid  is  noticed. 

2.  To  solution  add  ferric  chloride  :    a  brown  precipitate  is  formed. 

3.  Heat  the  dry  acid  with  calcium  hydroxide  in  a  test-tube :  ben- 
zene and  ammonia  are  evolved. 

4.  Evaporate  to  dryness  with  a  few  drops  of  nitric  acid  :  an  intense 
odor  of  nitrobenzene  is  evolved. 

Chlorides  in  urine.  Chlorides  are  present  in  larger  amount  than 
any  other  inorganic  constituent.  As  sodium  chloride  is  the  most 
abundant,  the  total  quantity  is  usually  expressed  in  terms  of  sodium 
chloride,  and  normally  amounts  to  10  to  15  grammes  in  twenty-four 
hours.  While  the  origin  of  the  chlorides  is  in  the  ingested  food,  they 
bear  some  relation  to  the  body  metabolism,  which  as  yet  is  not  un- 
derstood. In  nephritis  there  is  a  retention  of  chlorides,  particularly 
with  the  development  of  oedema.  In  pneumonia  there  is  a  great 
decrease  in  the  chlorides,  with  a  return  to  normal  amounts  at,  or  even 
slightly  before,  the  crisis.  The  significance  of  these  facts  is  not 
known.  4 

Qualitative  test  for  chlorides.     To  a  few  c.c.  of  urine,  acidified  with 
nitric  acid,  add  a  few  c.c.  of  5  per  cent,  silver  nitrate  solution.     A 


URINE  AND  ITS  CONSTITUENTS.  719 

white  precipitate  of  silver  chloride  forms.  By  comparing  the  result 
with  that  obtained  with  a  known  normal  urine,  a  rough  estimate 
can  be  gotten  as  to  the  amount  of  chlorides  present. 

Estimation  of  chlorides.  The  chlorides  in  a  measured  amount  of 
urine  are  precipitated  by  the  addition  of  an  excess  of  silver  nitrate 
solution  of  known  strength.  The  silver  chloride  is  removed  and  the 
amount  of  silver  nitrate  remaining  in  solution  is  determined  by  the 
method  given  on  page  427.  The  following  solutions  are  used  :  (1) 
Silver  nitrate  of  such  strength  that  1  c.c.  corresponds  to  0.01  gramme 
of  sodium  chloride.  (2)  Potassium  sulphocyante  of  such  strength  that 
1  c.c.  corresponds  to  1  c.c.  of  the  silver  solution.  (3)  Ammonio- 
ferric  alum,  saturated  solution. 

To  10  c.c.  of  urine  in  a  100  c.c.  graduated  flask  add  4  c.c.  of  con- 
centrated nitric  acid  and  50  c.c.  of  distilled  water.  Add  15  c.c.  of 
the  silver  solution  and  dilute  the  mixture  to  the  100  c.c.  mark,  shak- 
ing well.  Filter  off  50  c.c.  and  titrate  with  the  sulphocyanate  solu- 
tion, after  adding  3  c.c.  of  ammonio-ferric  alum.  The  result  multi- 
plied by  2  shows  the  number  of  cubic  centimeters  of  silver  nitrate 
which  was  in  excess.  The  difference  between  this  number  and  15 
is  the  number  of  cubic  centimeters  of  silver  nitrate  which  corresponds 
to  the  chloride  content  of  the  10  c.c.  of  urine. 

Phosphoric  acid  is  found  in  urine,  in  part  (about  two-thirds)  com- 
bined with  alkalies,  and  in  part  (about  one-third)  with  lime  and 
magnesia.  These  phosphates  have  in  acid  or  neutral  urine  the  com- 
position NaH2PO4,  CaH4(PO4)2,  MgH4(PO4)2 ;  in  amphoteric  urine, 
in  addition  to  the  above,  there  occur  Na2HPO4,  CaHPO4,  MgHPO4 ; 
in  alkaline  urine  compounds  of  the  composition  Na2HPO4,  CaHPO4, 
MgHPO4,  Na3PO4,  Ca3(PO4)2,  Mgs(PO4)2,  MgNH4PO4  may  be  pres- 
ent. A  small  quantity  is  present  as  glycerin-phosphoric  acid. 

The  phosphates  in  urine  amount  normally  to  about  3  grammes  of 
P2O5  in  twenty-four  hours.  They  are  derived  mainly  from  the  food, 
and  to  a  much  smaller  amount  from  the  body  protein.  They  are  in- 
creased in  certain  cases  of  diabetes,  and  are  decreased  in  most  of  the 
fevers.  The  determination  of  the  phosphatic  output  has  little  clinical 
importance. 

On  adding  any  alkali  the  phosphates  of  calcium  and  magnesium 
(generally  termed  earthy  phosphates)  are  precipitated  ;  the  phosphates 
of  sodium  or  possibly  potassium  remain  dissolved,  and  may  be  pre- 
cipitated as  magnesium  ammonium  phosphate  by  the  addition  of 
magnesia  mixture. 


720  PHYSIOLOGICAL  CHEMISTRY. 

Experiment  99.  (  Volumetric  determination  of  phosphoric  acid.)  Soluble 
uranium  salts  give  with  phosphates  a  dirty-white  precipitate  of  uranium  phos- 
phate :  Na2HPO4  +  UO2(NO3)2  =  UO2HPO4  +  2NaNO3.  The  precipitate  is 
soluble  in  mineral  acids,  insoluble  in  acetic  acid.  Tincture  of  cochineal  is  not 
affected  by  uranium  phosphate,  but  is  colored  greenish  by  soluble  uranium 
salts.  These  reactions  are  used  for  determining  phosphoric  acid,  thus  : 

Make  up  a  solution  of  sodium  acetate,  100  grammes  ;  acetic  acid  (glacial), 
30  grammes  ;  and  water  to  make  1000  c.c. 

Prepare  a  volumetric  solution  of  nitrate  or  acetate  of  uranium  so  adjusted 
that  1  liter  is  equivalent  to  5  grammes  of  P2O5.  To  100  c.c.  of  filtered  urine 
add  5  c.c.  of  the  acetate  solution  and  a  few  drops  of  solution  of  cochineal.  Heat 
to  boiling  and  titrate  with  uranium  solution  until  the  liquid  assumes  a  green 
color.  The  number  of  c.c.  required  multiplied  by  0.005  indicates  the  quantity 
of  P2O5  in  the  urine  used. 

Sulphur  in  the  urine.  Sulphur  is  present  in  the  urine  in  three 
forms  : 

Neutral  (unoxidized)  sulphur  ;  cystine,  etc. 
Oxidized  (acid)  sulphur  : 

a.  Inorganic  (preformed)  sulphates,  Na,  K,  etc. 

b.  Ethereal  (conjugate)  sulphates  ;  sulphuric  acid  in  combination 

with  skatole,  indole,  phenol,  etc. 

The  origin  of  the  urinary  sulphur  is  the  protein  metabolism,  while 
a  small  portion  may  arise  from  the  ingested  sulphates.  The  total 
amount  has  little  clinical  importance.  It  is  increased  in  fever  and 
with  a  meat  diet.  The  inorganic  sulphates  are  largely  in  excess, 
their  amount  being  about  ten  times  that  of  the  ethereal  sulphates. 

Experiment  100.  1.  Demonstrate  neutral  sulphur  by  adding  HC1  to  urine 
with  a  fragment  of  zinc  ;  hydrogen  sulphide  will  be  evolved  and  will  blacken 
lead  acetate  paper. 

2.  Demonstrate  inorganic  sulphates  by  adding  barium  chloride  solution  to 
urine  acidified  with  acetic  acid  ;  a  white  precipitate  of  barium  sulphate  will 
form.     Filter  this  solution  ;  and, 

3.  Demonstrate  ethereal  sulphates  by  adding  HC1  and  barium  chloride  solu- 
tion to  the  filtrate.     On  boiling  the  organic  sulphates  will  be  broken  up  and  a 
second  precipitate  of  barium  sulphate  will  form. 

Neutral  sulphur  in  the  urine.  While  there  is  normally  present 
about  10  per  cent,  of  the  total  sulphur  in  this  form,  the  bodies  which 
contain  it  are  so  far  almost  unknown.  Sulphocyanates  are  found 
in  small  amounts. 

Pathologically  the  best  known  body  is  cystine,  which  is  believed 
to  indicate  an  inability  on  the  part  of  the  body  to  completely  break 
down  the  protein  residues. 


Cystine,  diamino-dithw-dipropionic  acid,  ^'2       is 


URINE  AND  ITS  CONSTITUENTS.  721 

secreted  by  the  members  of  some  families,  and  seems  to  be  without 
pathological  significance,  except  that  it  may  be  deposited  in  the 
bladder  and  form  calculi. 

Cystine  is  insoluble  in  water,  alcohol,  and  ether,  but  is  readily  soluble  in 
ammonia- water  ;  boiled  with  solution  of  sodium  hydroxide  a  sulphide  of  sodium 
is  formed  which  stains  silver  black.  Cystine  crystallizes  in  characteristic  regu- 
lar six-sided  tablets,  and  is  best  recognized  microscopically  in  the  precipitate 
formed  by  adding  acetic  acid  to  urine.  Inorganic  sulphates  of  sodium,  potas- 
sium, and  magnesium  are  present,  but  possess  no  great  interest. 

Ethereal  sulphates.  As  the  conjugated  substances  (phenol,  para- 
cresol,  skatole,  indole,  etc.)  are  formed  in  the  intestine  as  putrefac- 
tion products  of  the  proteins,  and  are  conjugated  (in  the  liver)  merely 
for  excretion,  the  resulting  organic  sulphates  are  increased  whenever 
the  intestinal  putrefaction  is  increased.  The  estimation  of  these 
bodies  as  sulphates  is,  however,  seldom  carried  out,  as  the  increase  is 
important  only  when  it  is  marked,  and  it  is  simpler  to  show  an  in- 
crease of  the  non-sulphate  portion.  The  indican  tests  are  commonly 
made  use  of  in  this  connection. 

Indican,  indoxyl-sulphuric  add,  C8H7NSO4, 

/NH\ 

C6H  <^        ^CH  This  compound  is  not  identical  with  the 

XC^_O—  SO2.OH. 

indican  found  in  woad  and  a  few  other  plants.  The  vegetable  indican 
is  a  glucoside,  C26H31NO7,  yielding  by  fermentation,  among  other 
products,  dextrose  and  indigo-blue,  C16H10N2O2.  The  latter  is  iden- 
tical with  the  indigo  obtained  from  indoxyl-sulphuric  acid,  which 
decomposes  into  sulphuric  acid  (or  a  salt  of  it),  and  indoxyl,  which 
latter,  by  oxidation,  yields  indigo,  thus  : 

C8H6KNSO,    +    H,0    =    C8H7NO    +    KHSO4 

Potassium  Indoxyl. 

indoxy  1-sul  ph  ate. 

2(C8H7NO)     +    2O    =    C16H10N202     -f    2HjO 
Iiidoxyl.  Indigo. 

The  source  and  formation  of  indican  in  the  body  have  been  men- 
tioned. In  urine  it  occurs  normally  to  the  extent  of  0.002  per  cent., 
while  pathologically  the  quantity  may  be  much  greater.  Indican  is 
pale  yellow,  but  is  easily  converted  into  indigo-blue,  and  it  is  this 
property  which  is  used  for  its  detection. 

Tests  for  indican. 

1.  Mix  equal  volumes  of  urine  and  strong  hydrochloric  acid  ;  then 
add  drop  by  drop  a  solution  of  bleaching-powder  until  the  maximum 

Afi 


722  PHYSIOLOGICAL   CHEMISTRY. 

of  color  is  attained  ;  add  chloroform,  which  is  colored  blue.  (Care 
should  be  taken  to  add  the  hypochlorite  slowly,  as  an  excess  destroys 
the  color ;  highly  colored  urine  should  be  decolorized  with  basic  lead 
acetate  ;  in  doubtful  cases  the  mixture  of  urine,  hydrochloric  acid,  one 
or  two  drops  of  bleach  ing-powder  solution,  and  chloroform  should 
be  set  aside  for  several  hours.) 

2.  ObermayeSs  test  depends  on  the  conversion  of  indican  into  indigo 
by  ferric  chloride  ;  and  as  this  reagent  has  no  further  action  on  indigo, 
the  method  has  a  great  advantage  over  the  previous  ones.  The  test 
is  made  by  following  the  directions  given  in  the  above  test,  using  an 
equal  volume  of  strong  HC1  containing  0.2  per  cent,  of  ferric 
chloride  and  no  bleaching-powder  solution. 

Indigo-red  appears  in  the  urine  in  the  same  conditions  in  which 
indican  is  found.  It  is  recognized  by  Rosenbach's  reaction  :  Urine 
is  boiled,  and,  while  it  is  still  boiling,  nitric  acid  is  added  drop  by 
drop,  when  a  deep  red  color  appears  if  indigo-red  is  present.  The 
foam  on  shaking  the  test-tube  is  bluish  red. 

Skatole  (skatoxyl-sulphuric  acid)  is  rarely  present  in  the  urine.  Its 
formation  is  analogous  to  that  of  indole. 

Phenol,  C6H5OH,  and  paracresol,  C6H4.CH3.OH,  occur  in  urine 
in  combination  with  potassium  acid  sulphate.  The  combined  quan- 
tity of  the  two  substances  is  about  0.002  per  cent.  The  quantity  is 
increased  during  intestinal  putrefaction  from  all  causes  (except  simple 
obstruction),  when  there  is  absorption  of  pus  from  abscess  or  wounds, 
and  after  ingestiou  of  carbolic  acid. 

Experiment  101.  (Determination  of  phenol.} 

a.  Qualitative   determination.     Render  alkaline  100  c.c.  of  urine  with  sodium 
carbonate,  evaporate  to  a  syrup,  add  20  c.c.  of  hydrochloric  acid,  and  distill. 
To  the  distillate  apply  the  tests  for  phenol. 

b.  Quantitative  determination.     To  500  c.c.  of  urine  add  25  c.c.  of  hydrochloric 
acid  and  distill  200  c.c.     Neutralize  distillate  with  sodium  hydroxide,  in  order 
to  convert  benzoic  and  possibly  other  acids  present  into  salts,  and  again  distill 
200  c.c.     Determine  the  quantity  of  phenol  in  the  distillate  by  means  of  deci- 
normal  bromine  solution,  as  directed  on  page  424. 

Pyrocatechin,  ortho-dioxy  benzene,  C6H4(OH)2,  occurs  in  urine  as 
pyrocatechin  sulphuric  acid.  It  is  derived  from  the  putrefaction  of 
vegetable  food,  and  is  found  in  large  quantity  in  urine  after  taking 
carbolic  acid.  Urine  containing  pyrocatechin  turns  dark  on  exposure 
to  air,  especially  if  it  is  made  alkaline. 

To  show  the  presence  of  pyrocatechin,  add  a  little  sulphuric  acid 
to  the  urine,  boil,  and  when  cool  extract  with  ether.  Evaporate  the 
ether,  dissolve  the  residue  in  a  little  water,  and  apply  tests. 


URINE  AND  ITS  CONSTITUENTS.  723 

Tests  for  pyrocatechin. 

1 .  Add  dilute  ferric  chloride  solution  :  a  green  color  is  evolved. 
Add  a  little  tartaric  acid  and  then  ammonia :  the  green  color  changes 
to  violet,  but  on  acidifying  with  acetic  acid  the  green  color  reappears. 

2.  Add  sodium  hydroxide  :  the  solution  turns  green,  brown,  and 
black. 

3.  Add  lead  acetate :  pyrocatechin  is  precipitated  as  a  lead  com- 
pound. 

4.  Show  that  Fehling's  solution  and  ammonio-silver  nitrate  solu- 
tion are  reduced  by  pyrocatechin,  but  that  it  does  not  act  on  alkaline 
bismuth  solution. 

Sodium,  potassium,  calcium,  and  magnesium  occur  in  the  urine 
mainly  as  inorganic  salts.  They  are  derived  from  the  food.  The 
amount  present  is  not  important  clinically. 

Oxalic  acid.  The  source  of  this  acid  in  urine  is  unknown.  Many 
vegetables  and  fruits  contain  oxalates,  which,  after  ingestion,  are 
secreted  to  a  great  extent  unchanged.  That  oxalic  acid  occurs  as  a 
metabolic  product  is  shown  by  its  excretion  during  starvation,  and 
also  when  the  diet  is  exclusively  protein  and  fat.  It  is  believed  that 
the  protein,  and  not  the  fat,  is  concerned  here.  An  increased  elimi- 
nation of  oxalic  acid  occurs  in  diabetes,  icterus,  and  in  the  condition 
called  oxaluria. 

Enzymes  in  urine.  Pepsin  has  been  shown  to  be  present  in  small 
amount  in  normal  urine ;  lipase  and  a  diastase  have  been  found  in  a 
few  cases. 

Pathological  constituents.  While  the  normal  constituents  of 
urine,  and  especially  the  quantity  excreted  in  twenty-four  hours, 
give  valuable  information  in  regard  to  the  whole  process  of  metab- 
olism taking  place  in  the  body,  pathological  constituents  often  show 
with  great  precision  abnormal  conditions  existing  in  the  body,  and 
the  qualitative  or  quantitative  determination  of  pathological  con- 
stituents is  therefore  a  valuable  aid  in  diagnosing  disease.  Of  patho- 
logical constituents  are  of  chief  interest  the  proteins  (albumin,  globu- 
lin, albumoses,  peptones),  sugars,  and  the  constituents  of  blood  or 
bile.  But  many  other  substances  occur  at  times,  and  should  not 
be  overlooked  in  the  examination.  To  these  substances  belong 
acetone,  diacetic  acid,  melanin,  a  compound  giving  the  diazo-reac- 
tion,  etc. 


724  PHYSIOLOGICAL  CHEMISTRY. 

Proteins  in  urine.  Albumin  in  urine  is  always  serum-albumin, 
and  is  usually  associated  with  serum-globulin.  The  pathological  con- 
dition is  termed  albuminuria.  While  transient  albuminuria  may 
follow  severe  muscular  or  mental  strain,  cold  baths,  etc.,  and  leave 
no  permanent  effect,  it  must  always  be  regarded  as  a  pathological 
condition.  The  most  common  cause  of  continued  albuminuria  is  or- 
ganic disease  of  the  kidneys,  acute  and  chronic  nephritis,  or  even 
chronic  passive  congestion.  It  occurs  in  all  severe  febrile  conditions, 
in-  blood  diseases  (pernicious  anemia,  leukemia),  after  chloroform  and 
ether  anaesthesia,  and  after  many  poisons  (cantharides,  phenol,  etc.). 
Albumin  is  present  in  all  urines  containing  blood  or  pus  arising  from 
any  portion  of  the  urinary  tract. 

Tests  for  albumin. 

1.  Heat  and  acid.     Heat  to  boiling  the  upper  portion  of  urine  in  a 
test-tube.     If  a  cloud  appears  it  is  due  to  albumin  or  phosphates. 
The  lower  cold  urine  serves  as  a  guide  for  comparison.     If  no  cloud 
forms,  albumin  may  or  may  not  be  present ;  in  any  case  add  a  few 
drops  of  5  per  cent,  acetic  acid  until  the  reaction   is  acid — boiling 
again  after  each  drop.     A  cloud  already  present,  due  to  phosphates, 
will  disappear;  one  due  to  albumin  will  become  more  distinct.     In 
case  albumin  is  present,  but  has  not  already  been  coagulated,  it  will 
form  a  cloud  on  the  addition  of  the  acid,  showing  that  there  was  not 
sufficient  acid  present  originally,  the  urine  being  either  neutral  or 
alkaline.  The  test  is  made  more  delicate  by  the  addition  of  one-eighth 
of  the  volume  of  the  urine  of  saturated  salt  solution,  which  should 
always  be  done  with  very  dilute  urines.     It  is  important  to  avoid  an 
excess  of  the  acid,  as  the  coagulated  albumin  may  go  into  solution 
again.     If  the  test  is  made  with  the  addition  of  salt  solution,  it  is 
extremely  delicate  and  rarely  misleading.     The  acetic  acid  may  be 
replaced  Ijy  nitric  acid,  with  which  an  excess  of  acid   is  less  to  be 
feared,  and   fa   to  y1^  volume  of   concentrated  acid  can  be    added. 
With  nitric  acid  the  urine  should  not  be  boiled  after  the  acid  has 
been  added. 

2.  Nitric  acid  test.     About  20  c.c.  of  clear  urine  are  placed  in  a 
conical  test-glass  of  about  50  c.c.  capacity  ;  from  5  to  10  c.c.  of  nitric 
acid  are  added  by  means  of  a  pipette  in  such  a  manner  that  the  acid 
flows  slowly  from  the  pipette,  which  is  carried  to  the  bottom  of  the 
vessel.   Operating  carefully,  two  distinct  layers  of  liquid  are  obtained, 
and  in  the  presence  of  albumin  a  distinct  white  cloud  will  appear  at 


URINE  AND  ITS  CONSTITUENTS.  725 

the  zone  of  contact,  the  extent  and  intensity  of  the  cloud  varying 
with  the  quantity  of  albumin  present.  Very  small  quantities  of 
albumin  cannot  be  detected  at  once,  but  will  appear  on  standing,  the 
cloudiness  extending  gradually  upward.  A  distinct  ring  from  1  to  2 
cm.  above  the  zone  of  contact,  and  appearing  within  five  to  ten 
minutes  after  the  addition  of  nitric  acid,  was  formerly  thought  to  be 
due  to  uric  acid,  and  was  called  the  urate  ring.  It  is  believed  now 
to  be  in  some  cases  composed  of  protein  material.  In  urines  contain- 
ing a  high  percentage  of  urea,  a  ring  may  form  at  the  plane  of  con- 
tact, consisting  of  urea  nitrate,  which  is  distinctly  crystalline  in 
appearance.  Following  the  ingestion  of  turpentine  and  various  bal- 
sams, this  test  may  show  a  precipitate  of  resinous  acids  at  the  junc- 
tion of  urine  and  acid,  which  is  recognized  by  its  solubility  in  alcohol 
or  ether.  Albumoses  produce  a  ring  which  dissolves  on  heating  and 
reappears  on  cooling. 

At  the  zone  of  contact  a  change  in  color  is  generally  noticed.  In 
normal  urine  this  varies  from  pale  red  to  intense  brick  red ;  in  biliary 
urine  a  color- play  similar  to  the  colors  of  the  rainbow  may  be  noticed, 
while  the  presence  of  indican  is  indicated  by  a  violet  or  blue  tint. 
It  is  important  to  distinguish  between  color  rings  and  precipitate 
rings. 

3.  Trichlor acetic  acid  may  be  used  for  the  detection  of  albumin  by 
dropping  a  fragment  into  a  few  cubic  centimeters  of  urine  contained 
in  a  test-tube.    As  the  acid  dissolves,  a  cloudy  ring  forms  in  the  pres- 
ence of  albumin,  which  is  not  dissolved  on  warming. 

4.  Potassium  ferrocyanide  test.     5  to  lOc.c.  of  cold  urine  are  acidu- 
lated with  5  to  10  drops  of  acetic  acid,  and  to  the  mixture  are  added 
a  few  drops  of  solution  of  potassium  ferrocyanide.     In  the  presence 
of  even  traces  of  albumin  a  turbidity  is  caused.     A  precipitate  which 
dissolves  on  heating  is  due  to  albumose.     This  test  is  extremely  deli- 
cate, especially  when  modified  so  as  to  allow  a  few  cubic  centimeters 
of  diluted  acetic  acid,  to  which  a  few  drops  of  potassium  ferrocynaide 
solution  had  been  added,  to  flow  down  the  side  of  the  test-tube  con- 
taining the  urine.     A  decided  turbidity  at  the  point  of  contact  of  the 
two  liquids  shows  albumin. 

In  case  the  addition  of  acetic  acid  to  the  cold  urine  should  cause  a 
turbidity  (which  may  be  due  to  mucin  or  nucleo-albumin)  it  must  be 
filtered  before  adding  the  potassium  ferrocyanide. 

In  the  above  methods  the  manipulations  and  precautions  are  mi- 
nutely described,  in  order  to  detect  small  quantities  or  even  traces  of 
albumin.  When  albumin  is  abundantly  present,  there  is  no  difficulty 


726  PHYSIOLOGICAL   CHEMISTRY. 

whatever  in  its  detection,  as  heat  will  precipitate  it  in  most  cases  from 
an  acid,  neutral,  or  sometimes  even  alkaline  urine  ;  the  precipitate 
should,  however,  always  be  tested  by  the  addition  of  a  few  drops  of 
nitric  acid,  and  the  previous  addition  of  a  few  drops  of  acetic  acid  is 
also  advisable. 

Quantitative  estimation  of  albumin.  The  average  amount  of 
albumin  present  in  acute  cases  of  albuminuria  is  0.1  to  0.5  per  cent., 
rarely  over  1  per  cent.,  though  it  may  rise  to  4  per  cent.  An 
approximate  method  for  the  comparative  estimation  of  albumin  is  to 
precipitate  it  (with  the  precautions  above  given)  in  a  graduated  test- 
tube  by  heat  and  setting  aside  for  twelve  (or,  better,  for  twenty-four) 
hours.  At  the  end  of  that  time  the  proportion  of  the  coagulated 
albumin  which  has  collected  at  the  bottom  of  the  fluid  is  noticed.  If 
the  albumin  occupy  one-fourth,  one-sixth,  one-tenth  of  the  height  of 
the  liquid,  there  is  said  to  be  one-fourth,  one-sixth,  or  one-tenth  of 
albumin  in  the  urine.  If,  however,  at  the  end  of  twelve  or  twenty- 
four  hours  scarcely  any  albumin  has  collected  at  the  bottom,  there  is 
said  to  be  a  trace. 

The  volumes  of  coagulated  albumin  indicate  the  following  quantities  of  dry 
albumin : 

Slight  turbidity  indicates  about 0.01  per  cent. 

&  of  tbe  tube  is  filled 0.05  " 

rV  "  "  .......  0.10  " 

j  «    •       *  0.25 

I  "  "  .......  0.50  " 

£  "  "  .......  1.00  " 

Complete  coagulation .  2  to  3  " 

Esbach's  albuminometer  (Fig.  75)  is  a  conveniently  arrnnged  tube  for  deter- 
mining approximately  the  quantity  of  albumin.  The  tube  is  rilled  with  urine  to 
U,  and  then  with  the  reagent  to  R.  The  reagent  is  a  solution  containing  1 
gramme  of  picric  acid  and  2  grammes  of  citric  acid  in  100  c.c.  of  water.  After 
having  filled  the  tube  it  is  closed  with  a  stopper,  inverted  twelve  times,  and  set 
aside  for  twenty-four  hours.  At  the  end  of  that  time  the  albumin  will  have 
settled  down,  when  the  amount  pro  mille  in  grammes  may  be  directly  read  off 
from  the  scale. 

Tsuchiya's  reagent  possesses  many  advantages  over  Esbach's,  and  is  used  in 
the  same  manner.  It  is,  Phosphotungstic  acid,  1.5  grammes;  hydrochloric 
acid  (concentrated),  5  c.c.;  alcohol,  95  c.c. 

A  better  method  of  exactly  estimating  the  amount  of  albumin  is  its 
complete  separation  and  weighing,  as  described  below. 

Experiment  102.  Acidify  100  c.c.  of  clear  albuminous  urine  with  acetic  acid ; 
heat  to  the  boiling-point  in  a  water-bath  for  half  an  hour,  and  filter  through  a 


URINE  AND  ITS  CONSTITUENTS. 


727 


small  filter,  previously  dried  at  110°  C.  (230°  F.)  and  weighed  ;  wash  with  boil- 
ing water  to  which  a  little  ammonia  water  has  been  added  (to  remove  uric 
acid  and  urates),  then  with  pure  water  until  the  filtrate  is  not  rendered  turbid 
any  longer  by  silver  nitrate,  next  with  pure  alcohol,  and  finally  with  ether. 
Dry  filter  and  contents  at  110°  C.  (230°  F.)  and  weigh. 

As  it  may  happen  that  the  precipitated  albumin  encloses  earthy  phosphates, 
it  is  well  to  burn  filter  with  contents  in  a  platinum  crucible,  and  to  deduct  the 
weight  of  the  remaining  inorganic  residue  (less  the  weight  of  the  filter  ash) 
from  that  of  the  albumin. 

Serum-globulin  is  detected  by  rendering  the  urine  alkaline  with 
ammonia   water,  filtering  off  the  precipitate  of  phosphates,  and  add- 
ing to  the  clear  filtrate  an  equal  volume  of  a  saturated 
solution  of  ammonium  sulphate.     The  appearance  of  a        FIG.  75. 
precipitate  indicates  globulin. 

Albumoses  answer  to  the  nitric  acid  test  and  the 
potassium  ferrocyanide  test  for  albumin ;  the  precip- 
itate formed  by  these  reagents  dissolves  on  heating, 
but  reappears  on  cooling.  Albumoses  are  further  rec- 
ognized thus :  To  the  urine  strongly  acidified  with  hydro- 
chloric acid  is  added  an  equal  volume  of  a  saturated  so- 
lution of  sodium  chloride.  On  boiling,  serum-albumin, 
if  present,  is  precipitated  and  filtered  off  while  hot. 
Albumoses  separate  from  the  filtrate  on  cooling. 

The  solution,  filtered  while  hot,  gives  a  red  biuret 
reaction.  As  albumose  is  frequently  present  in  albu- 
minuria,  its  demonstration  is  important  only  in  the 
absence  of  albumin.  Albumosuria  occurs  with  the 
absorption  of  purulent  exudates,  in  acute  yellow  atrophy 
of  the  liver,  and  in  other  conditions. 

Peptones  are  not  uncommonly  present  in  the  urine  aibuminometer. 
in  albumosuria,  but  are  rarely  present  alone.  Peptonuria 
exists  when  it  is  possible  to  obtain  a  red  biuret  reaction  after  the 
careful  removal  of  protein  and  albumose.  Both  here  and  in  the  case 
of  albumosuria  urobilin  may  mislead  one  when  the  biuret  reaction  is 
tried.  It  may  be  removed  by  extraction  with  alcohol. 

Bence- Jones  body  is  present  in  the  urine  in  certain  cases  of 
bone  disease  (multiple  myeloma).  It  is  thought  to  be  a  unique 
albumin  and  not  an  albumose,  as  held  by  the  earlier  view.  It  is 
coagulated  in  urine  acidified  with  acetic  acid  on  heating  to  50°  or 
60°  C.,  and  redissolves  as  the  temperature  reaches  the  boiling-point. 
It  is  very  rarely  present. 


Esbach's 


728  PHYSIOLOGICAL   CHEMISTRY. 

Nucleo-albumin.  If  the  ring  occurring  in  Heller's  test  some  dis- 
tance above  the  place  of  contact  becomes  more  distinct  when  the 
urine  is  diluted,  it  is  believed  to  be  of  protein  origin,  and  has  been 
called  nucleo-albumin,  mucin,  euglobulin,  Morner's  body,  etc.  Its 
true  nature  is  not  yet  known.  The  cloud  produced  by  acetic  acid 
in  the  cold  is  believed  to  be  due  to  the  same  body.  As  urates  may 
be  precipitated  in  both  of  these  methods,  it  is  important  to  rule  them 
out  by  diluting  the  urine,  when  the  precipitate  due  to  urates  will  not 
appear.  True  nucleo-albuminuria  is  rare. 

Blood.  The  presence  of  blood  in  urine  manifests  itself  generally, 
unless  the  amount  be  too  slight,  by  a  blood-red  or  browrnish  color 
with  a  bluish,  smoky,  or  greenish  tint,  and  deposits  a  red  or  reddish- 
brown  sediment  after  standing.  As  a  general  rule,  all  constituents 
of  blood,  including  the  corpuscles,  are  present  (haematuria),  but  in 
some  cases  only  haemoglobin  (methaemoglobin)  is  found  (haemoglobin- 
uria). 

The  tests  for  blood  depend  either  on  the  microscope,  spectroscope, 
or  on  chemical  changes.  By  the  microscope  is  examined  the  deposit 
which  forms  on  standing ;  almost  unaltered  blood-corpuscles  may  be 
found,  or  they  may  be  much  swollen,  decolorized,  and  deformed. 

Haematuria  is  common  and  occurs  in  diseases  of  the  kidney  (acute 
nephritis,  stone,  tuberculosis,  trauma) ;  similar  conditions  of  the  ure- 
ters and  bladder ;  general  conditions  (malignant  forms  of  smallpox, 
malaria,  etc. ;  haemophilia). 

Haemoglobinuria  occurs  occasionally  in  severe  fevers  (scarlet  fever, 
yellow  fever) ;  after  severe  burns  or  exposure  to  cold  ;  in  certain 
poisonings  (potassium  chlorate,  carbon  monoxide).  It  is  always  pre- 
ceded by  haemoglobinaemia,  i.  6.,  the  presence  of  free  haemoglobin  in 
the  circulating  blood.  The  spectroscope  shows  the  absorption-bands 
of  the  blood-pigments,  for  which  see  Fig.  72. 

Tests  for  blood  in  urine. 

1.  Render  alkaline  with  sodium  hydroxide  and  boil.     In  the  pres- 
ence of  blood  coloring-matter  the  precipitate  of  phosphates  produced 
is  colored  red.     In  a  urine  containing  other  coloring-matters  (bile- 
pigments,  etc.)  the  test  may  be  misleading ;  in  such  cases,  filter  off 
the  precipitate,  wash,  and  dissolve  it  in  acetic  acid.     In  the  presence 
of  blood-pigment  the  solution  becomes  red,  but  the  color  gradually 
disappears  on  exposure  to  air. 

2.  Allow  a  mixture  of  freshly  prepared  tincture  of  guaiacum  and 


URINE  AND  ITS  CONSTITUENTS.  729 

ozonized  oil  of  turpentine  to  flow  down  the  side  of  a  test-tube  in 
such  a  manner  as  to  form  a  distinct  layer  above  the  urine.  A  white 
ring,  gradually  turning  blue,  will  appear  at  the  surface  of  contact. 
(Ozonized  oil  of  turpentine  is  oil  which  has  been  exposed  to  air  for 
some  time ;  in  place  of  it  may  be  used  peroxide  of  hydrogen  or  a 
mixture  of  this  compound  with  ether.) 

3.  Add  a  little  of  a  solution  of  egg-albumin  to  100  c.c.  of  urine, 
heat  to  boiling,  and  filter  off  the  coagulum,  which  has  taken  up  the 
hsematin.  Mix  the  precipitate  in  a  mortar  with  20  c.c.  of  absolute 
alcohol  and  a  few  drops  of  sulphuric  acid,  transfer  to  a  flask,  heat 
to  boiling,  and  filter.  After  cooling,  render  alkaline  with  sodium 
hydroxide,  reduce  with  ammonium  sulphide,  and  examine  spectro- 
scopically  for  reduced  ha3matin.  (Fig.  72.) 

The  direct  spectroscopic  examination  of  urine  is  generally  unsatisfactory> 
because  it  often  contains  a  number  of  substances  giving  absorption  spectra. 

Carbohydrates  in  urine.  Dextrose  (glucose)  in  urine  is  normally 
present  in  minute  amount.  When  the  amount  is  sufficient  to  give 
the  customary  reduction  tests,  the  condition  is  spoken  of  as  glyco- 
suria.  If  dextrose  be  eaten  in  large  amount  the  body  is  unable  to 
burn  all  of  it,  and  a  temporary  glycosuria  results.  This  is  called  ali- 
mentary glycosuria  and  is  not  a  serious  condition.  The  amount  of 
sugar,  the  "  assimilation  limit,"  which  can  be  ingested  without  the 
appearance  of  the  sugar  in  the  urine,  differs  for  the  different  sugars 
and  differs  in  different  individuals.  A  more  serious  condition,  per- 
sistent glycosuria,  exists  in  diabetes  when  the  body  is  unable  to  carry 
on  the  normal  sugar  metabolism.  In  this  disease  the  amount  of  dex- 
trose in  the  urine  may  be  very  large,  and  frequently  dextrose  is 
present,  even  when  the  patient  is  on  a  carbohydrate-free  diet.  In 
both  of  these  conditions  the  glycosuria  is  secondary  to  an  increase 
in  the  dextrose  content  of  the  blood,  while  in  experimental  "  phlorid- 
zin  diabetes  "  the  change  is  in  the  kidneys,  and  there  is  no  increase 
in  the  dextrose  of  the  blood. 

There  are  many  tests  by  which  dextrose  can  be  detected.  They 
depend  chiefly  on  the  following  properties  of  dextrose,  viz. :  1,  to  act 
as  a  deoxidizing  or  reducing  agent  upon  certain  metallic  oxides  (cop- 
per, bismuth,  silver,  mercury)  in  the  presence  of  alkalies ;  2,  to  pro- 
duce a  yellow  or  brown  color  when  in  contact  with  alkalies,  slowly 
in  the  cold,  rapidly  on  heating ;  3,  to  ferment  with  yeast ;  4,  to  unite 
with  phenyl-hydrazine  to  a  crystalline  compound;  5,  to  have  the 
power  of  rotating  the  plane  of  polarization  to  the  right. 


730  PHYSIOLOGICAL  CHEMISTRY. 

Tests. 

1.  Trommer's  test.     A  few  drops  (2-4)  of  a  5  per  cent,  solution  of 
cupric  sulphate  are  added  to  about  5  to  8  c.c.  of  urine  in  a  test-tube 
and  then  an  equal  volume  of  potassium  (or  sodium)  hydroxide  solu- 
tion is  added.     The  alkaline  hydroxide  precipitates  both  earthy  phos- 
phates and  cupric  hydroxide,  the  latter,  however,  dissolving  (espe- 
cially if  sugar  be  present)  in  the  excess  of  the  alkali,  producing  a 
beautiful  blue  transparent  liquid.     (If  no  sugar  is  present,  the  color 
is  less  blue,  but  more  of  a  greenish  hue.)     The  liquid  is  now  heated, 
when,  if  sugar  be  present,  a  yellow  precipitate  of  cuprous  hydroxide 
is  formed  which  subsequently  loses  its  water  and  becomes  the  red 
cuprous  oxide,  which  falls  to  the  bottom  or  adheres  to  the  sides  of 
the  test-tube.     (Plate  VIII.,  5.) 

In  drawing  conclusions  from  the  above  test,  it  should  be  remem- 
bered that  a  change  of  color  does  not  indicate  sugar ;  that  a  precipi- 
tate of  earthy  phosphates  must  not  be  mistaken  for  cuprous  oxide ; 
and  that  substances  other  than  sugar  may  deoxidize  cupric  oxide  at 
the  temperature  of  100°  C.  (212°  F.). 

A  disadvantage  of  Trommer's  test  is  the  formation  of  black  cupric 
oxide  whenever  too  much  copper  solution  is  used  in  proportion  to  the 
sugar  present.  The  formation  of  the  black  oxide,  which  may  mask 
a  small  quantity  of  cuprous  oxide,  is  avoided  in  the  next  test. 

2.  Fehling's  test  differs  from  Trommer's  test  in  merely  using  a  pre- 
viously mixed  reagent  instead  of  producing  this  reagent,  as  it  were, 
in  the  urine  by  adding  to  it  cupric  sulphate  and  an  alkaline  hydroxide 
successively.    This  reagent,  known  as  Fehling's  solution,  or  as  alkaline 
cupric  tartrate  volumetric  solution,  is  made  by  mixing  exactly  equal 
volumes  of  the  below-mentioned  copper  solution  and  the  Rochelle 
salt  solution  at  the  time  required. 

Copper  solution : 

Crystallized  cupric  sulphate 34.64  grammes. 

Water,  sufficient  quantity  to  make    ....     500  c.c. 

Rochelle  salt  solution : 

Potassium  sodium  tartrate 173  grammes. 

Potassium  hydroxide     .         .         .         .         .         .         .125         " 

Water,  sufficient  quantity  to  make          ....     500  c.c. 

Both  solutions  are  preserved  in  small  well-stoppered  bottles,  and 
mixed  only  at  the  time  needed,  because  the  mixture  is  apt  to  decom- 
pose when  kept  some  time. 

The  addition  of  sodium-potassium  tartrate  in  Fehling's  solution  prevents  the 
precipitation  of  cupric  hydroxide  by  the  alkaline  hydroxide.  This  action  is  anal- 


URINE  AND  ITS  CONSTITUENTS.  731 

ogous  to  the  formation  of  the  soluble  scale  compounds  of  iron,  where  the  pre- 
cipitation of  ferric  hydroxide  is  also  prevented  by  tartaric  or  other  organic  acids. 

The  test  is  made  by  heating  in  a  test-tube  10  c.c.  of  Folding's  solu- 
tion which  has  been  diluted  with  2  to  5  volumes  of  water  and  add- 
ing drop  by  drop  the  suspected  urine ;  if  the  latter  contains  larger 
quantities  of  sugar,  a  yellow  or  red  precipitate  of  cuprous  hydroxide 
and  oxide  will  be  produced  very  readily ;  if  but  small  quantities  are 
present,  the  reaction  will  appear  only  on  standing  for  some  time. 

Haines'  test  is  a  modification  of  Fehling's  test.  The  reagent  is  as 
follows :  "  Dissolve  30  grains  of  cupric  sulphate  in  \  ounce  of  water, 
add  \  ounce  of  glycerin  and  then  5  fluidounces  of  liquor  potassse." 
The  advantage  of  the  reagent  is  that  it  is  very  stable.  It  should  be 
used  by  boiling  about  1  drachm  in  a  test-tube,  adding  8  to  10  drops 
of  the  suspected  urine,  and  again  bringing  to  a  boil.  In  the  presence 
of  sugar  a  precipitate  of  cuprous  oxide  is  thrown  down. 

3.  Botgcr's  bismuth  test  consists  in  adding  to  a  mixture  of  equal 
volumes  of  urine  and  potassium  (or  sodium)  hydroxide  solution  a  few 
grains  of  subnitrate  of  bismuth  and  boiling  for  half  a  minute.     If 
sugar  be  present,  a  gray  or  dark -brown,  finally  black,  precipitate  of 
bismuthous  oxide,  Bi2O2,  or  of  metallic  bismuth  is  formed.     If  but 
very  little  sugar  is  present,  the  undecomposed  excess  of  bismuthic 
nitrate  (or  bismuthic  hydroxide)  mixes  with  the  metallic  bismuth, 
imparting  to  it  a  gray  color ;  the  test  should  then  be  repeated  with  a 
smaller  amount  of  the  bismuth  salt.     (Plate  VIII.,  6.) 

The  above  test  may  be  advantageously  modified  by  using  a  bismuth 
solution  instead  of  the  powder.  The  solution  known  as  Nylander's 
reagent  is  made  by  dissolving  2  grammes  of  bismuth  subnitrate,  4 
grammes  of  Rochelle  salt,  and  10  grammes  of  sodium  hydroxide  in 
90  c.c.  of  water,  and  filtering.  One-half  c.c.  of  this  solution  is  heated 
with  about  5  c.c.  of  urine,  when,  in  the  presence  of  sugar,  a  brown 
or  black  precipitate  will  form  after  a  few  minutes7  boiling. 

If  the  urine  contains  hydrogen  disulphide  (sometimes  produced  by  decom- 
position of  certain  urinary  constituents),  black  bismuth  sulphide  will  be  formed, 
which  may  be  mistaken  for  metallic  bismuth ;  albumin  itself  may  be  the  cause 
of  the  formation  of  alkaline  sulphides :  the  previous  complete  separation  of 
albumin  is  therefore  indispensable. 

4.  Moore's  or  Heller's  test  is  made  by  heating  urine  with  about 
one-fourth  its  volume  of  solution  of  potassium  hydroxide.     In  the 
presence  of  sugar  the  color  of  the  mixture  will  deepen  to  a  dark  yel- 
low or  brown,  and  the  depth  of  color  is  a  fair  indication  of  the  quan- 


732  PHYSIOLOGICAL   CHEMISTRY. 

tity  of  sugar  present.  In  case  but  a  slight  change  takes  place  in 
color,  it  is  well  to  compare  it  with  that  of  an  unchanged  specimen 
of  the  urine. 

5.  Fermentation  test.  This  is  based  upon  the  decomposition  of 
dextrose  by  yeast  with  the  generation  of  carbon  dioxide.  A  piece 
of  yeast  about  the  size  of  a  pea  is  ground  up  in  urine  and  the  mixture 
used  to  fill  a  fermentation  tube.  The  tube  is  then  kept  for  twenty- 
four  hours  at  a  fairly  constant  temperature  of  22°  to  28°  C.  If  dex- 
trose be  present,  fermentation  will  commence  within  twelve  hours 
and  will  manifest  itself  by  the  formation  of  carbon  dioxide  gas,  which 
will  collect  at  the  upper  end  of  the  long  arm  of  the  tube. 

The  urine  and  the  fermentation  apparatus  should  be  sterilized  by  heat  to 
destroy  any  gas-producing  bacteria  present.  For  a  control  of  the  test,  two 
more  fermentation  tubes  should  be  prepared,  one  with  a  mixture  of  a  glucose 
solution  and  yeast  (to  determine  that  the  yeast  is  efficient),,  and  another  with 
sterilized  water  and  yeast  (to  show  that  the  yeast  itself  does  not  generate 


The  disadvantages  of  this  process  are  the  length  of  time  required  for  its  per- 
formance, the  unreliability  of  the  ferment,  and  the  fact  that  small  quantities 
of  sugar  (less  than  0.5  per  cent.)  evolve  so  little  carbon  dioxide  that  a  doubt 
may  be  felt  as  to  the  presence  of  sugar  at  all. 

6.  The  pTienyl-Tiydrazine  test.     To  10  c.c.  of  urine  in  a  test-tube, 
add  phenyl-hydrazine  hydrochloride,  0.4  gramme  and  sodium  ace- 
tate, 1  gramme,  warm  until  dissolved,  adding  water,  if  necessary,  and 
keep  in  a  boiling  water-bath  for  half  an  hour.     Filter  while  hot,  and 
allow  to  cool  slowly.     The  presence  of  dextrose  will  be  shown  by  the 
deposition  of  yellow  crystals,  which  are  seen  with  the  microscope  to 
be  needles  arranged   in   sheaves.      This   precipitate   is   an    osazone 
(phenyl-dextrosazone)  and  melts  at  205°  C.      Pentoses  and  maltose 
give  similar  osazones,  as  do  lactose  and  glycuronic  acid.     The  latter 
are  rarely  present  in  sufficient  amount  to  give  a  positive  test  with  the 
urine  directly.     The  melting-points  are  of  value  in  recognizing  the 
different  osazones. 

7.  Polariscopic  test.     Before  urine  can  be  examined  by  the  polari- 
scope  it  should  be  freed  from  proteins  and  from  the  greater  part  of 
coloring-matters   by   precipitation   with   neutral    lead    acetate.     The 
sensitiveness  of  the  test  depends  on  the  construction  of  the  instru- 
ment, but  even  the  best  polarimeters  do  not  show  traces  of  sugar, 
for  which  reason  it  is  generally  useless  to  apply  the  test  unless  sugar 
has  been  indicated  bv  other  tests. 


URINE  AND  ITS  CONSTITUENTS. 


733 


The   following  table  shows  the  tests  for  distinguishing  dextrose 
from  other  reducing  agents  occurring  in  the  urine  : 


Fehling's  test. 

Bismuth  test. 

Fermenta- 
tion test. 

I'hfiivl-hv-     Polarisropic 
drazine  test.           test. 

Dextrose    . 

Reduction 

Reduction 

Positive 

Positive 

f  Dextro- 

\     rotatory 

Pentoses     . 

Reduction 

Reduction 

Negative 

Positive 

(  Dextro- 
\     rotatory 

Lactose 

Reduction 

Reduction 

Negative 

Positive 

f  Dextro- 
1     rotatory 

Laevulose   . 

Reduction 

Reduction 

Positive 

Positive 

f  Lsevo- 

(partial) 

\     rotatory 

!Laevo-ro- 

Glycuronic  acid 

Reduction 

Reduction 

Negative 

Positive 

tatoryin 

urine 

Alkaptonic  acids 
Uric  acid  . 
Creatinine 
Pyrocatechin 

Reduction 
Reduction 
Reduction 
Reduction 

Negative 
Negative 
Negative 
Negative 

Negative 
Negative 
Negative 
Negative 

Negative 
Negative 
Negative 
Negative 

Inactive 
Inactive 
Inactive 
Inactive 

Allantoin  . 

Reduction 

Negative 

Negative 

Negative 

Inactive 

Quantitative  estimation  of  sugar.  By  far  the  best  method  is 
the  decomposition  of  a  copper  solution  of  a  known  strength,  and 
Fehling's  solution  prepared  as  stated  above,  answers  this  purpose 
well. 

1000  c.c.  of  Fehling's  solution,  containing  34.64  grammes  of  crys- 
tallized cupric  sulphate,  CuSO4.5H2O,  are  decomposed  by  5  grammes 
of  grape-sugar,  or  1  c.c.  of  solution  by  0.005  of  grape-sugar. 

To  make  the  quantitative  determination,  operate  as  follows  :  10  c.c. 
of  Fehling's  solution  are  poured  into  a  porcelain  dish  of  about  200  c.c. 
capacity,  placed  over  a  flame.  The  copper  solution  is  diluted  with 
about  40  c.c.  of  water,  and  heated  to  boiling  ;  to  the  boiling  liquid, 
urine  (which  has  been  previously  diluted  with  9  parts  of  water)  is 
added  from  a  burette  very  gradually,  until  the  blue  color  of  the  solu- 
tion has  disappeared,  and  there  remains,  upon  subsidence  of  the 
cuprous  oxide,  an  almost  colorless,  clear  liquid.  A  filtered  portion 
of  this  liquid,  acidified  with  hydrochloric  acid,  should  not  give  a 
reddish-brown  precipitate  with  potassium  ferrocyanide  (a  precipitate 
would  show  that  all  copper  had  not  been  precipitated,  and  that  more 
urine  was  needed),  while  a  second  portion  of  the  filtered  fluid  should 
not  produce  a  red  precipitate  on  boiling  with  a  few  drops  of  Fehling's 
solution  (a  precipitate  would  indicate  that  too  much  urine  had  been 
added,  in  which  case  the  operation  has  to  be  repeated). 

The  calculation  of  the  amount  of  sugar  present  is  easily  made. 
10  c.c.  of  Fehling's  solution  are  decomposed  by  0.05  gramme  of 
sugar ;  this  quantity  must,  therefore,  be  contained  in  the  number  of 


734  PHYSIOLOGICAL  CHEMISTRY. 

c.c.  of  urine  used.  Suppose  30  c.c.  of  urine,  diluted  with  9  parts  of 
water,  or  3  c.c.  of  pure  urine,  have  been  required  to  decompose  the  10 
c.c.  of  Fehling's  solution,  then  3  c  c.  of  urine  contain  of  grape-sugar 
0.05  gramme,  or  100  c.c.  of  urine  1.666  grammes,  according  to  the 
proportion  : 

3    :    0.05    :  :     100    :    x 

1  =  1.666. 

If  the  urine  contains  but  very  little  sugar,  it  may  be  used  directly 
without  diluting  it,  or  instead  of  diluting  it  with  9  parts  of  water,  it 
may  be  diluted  with  4  volumes  or  with  an  equal  volume  of  water. 

In  using  Fehling's  solution  for  the  volumetric  estimation  of  lactose, 
it  should  be  remembered  that  1  c.c.  of  solution  is  decomposed  by 
0.0067  gramme  of  lactose. 

Modified  Fehling  method  (Rudisch  and  Celler).  The  only  change  is 
in  diluting  the  10  c.c.  of  Fehling  solution  with  40  c.c.  of  50  per 
cent,  potassium  stilphocyanate  instead  of  with  40  c.c.  of  water.  The 
end-reaction  here  is  the  same,  i.  e.,  the  disappearance  of  the  blue.  As 
there  is  no  precipitate  to  obscure  the  end-point,  the  estimation  is 
readily  made  and  the  method  is  an  improvement  over  the  original 
procedure.  As  the  same  amount  of  Fehling's  solution  is  used,  the 
calculation  is  carried  out  in  the  same  way. 

Harvey  G.  Beck  has  devised  the  following  method  : 

The  apparatus  used  consists  of  a  suitable  beaker ;  four  centrifugal  tubes 
graduated  at  2  c.c. ;  a  pipette  of  2  c.c.  capacity,  graduated  into  twentieths  c.c., 
and  a  wire  tube-holder  to  support  the  tubes  when  placed  in  the  beaker.  A 
centrifuge  will  greatly  facilitate  the  work. 

The  procedure  is  as  follows :  The  beaker,  one-third  full  of  water,  is  placed 
over  a.Bunseu  flame,  and  the  four  centrifugal  tubes,  after  being  filled  to  the 
graduation  mark  (2  c.c.)  with  standard  Fehling's  solution,  are  placed  in  the 
tube-holder  and  suspended  in  the  beaker.  The  tubes  are  numbered  respectively 
1,  2,  3,  and  4,  according  to  their  position  in  the  tube-holder.  The  urine  is  added 
from  the  pipette  in  quantities  of  twentieths  c.c.,  as  follows:  fa  to  No.  1,  -fa  to 
No.  2,  fa  to  No.  3,  and  -fa  to  No.  4.  The  tubes,  after  being  thoroughly  shaken, 
are  suspended  in  boiling  water  for  at  least  three  minutes,  when  they  are  removed 
and  either  set  aside  in  the  tube-stand  until  the  cupric  oxide  is  precipitated,  or 
centrifugalized  in  order  to  hasten  precipitation.  If  all  the  tubes  still  show  a 
blue  color,  the  urine  is  increased  to  ^,  -fa,  $%,  and  fa  respectively,  by  adding 
•fa  e.c.  to  each  tube,  and  the  foregoing  steps  are  repeated.  This  process  is  con- 
tinued until  one,  or  more,  of  the  tubes  is  completely  decolorized.  The  first  tube 
in  the  series  in  which  the  blue  color  has  entirely  disappeared  is  noted;  the 
number  of  twentieths  c.c.  required  to  reduce  it,  divided  into  twenty,  gives  the 
percentage  of  sugar  present. 

Estimation  by  fermentation  can  be  readily  done,  using  specially 
graduated  tubes,  which  can  be  read  directly  in  percentages  of  dextrose. 


URINE  AND  ITS  CONSTITUENTS.  735 

Estimation  by  means  of  the  polariscope  furnishes  the  quickest  method ; 
the  details  cannot  be  given  here. 

Other  carbohydrates  in  urine.  Laevulose  is  rarely  present  in  the 
urine;  in  almost  all  of  the  cases  dextrose  is  also  presen  t(diabetes). 
Laevulosuria  should  be  suspected  when  a  urine  reduces  copper  solu- 
tions, rotates  polarized  light  to  the  left  or  not  at  all,  and  shows  no 
Ia3vorotation  after  being  fermented. 

Lsevulose  reduces  copper  and  bismuth  solutions,  ferments  with 
yeast,  is  laevorotatory,  and  forms  the  same  osazone  with  phenyl- 
hydrazine  as  is  formed  by  dextrose. 

Maltose  is  very  rarely  present  in  urine.  Such  urines  show  a 
higher  percentage  of  sugar  with  the  polariscope  than  with  Fehling's 
solution. 

Lactose  occurs  in  the  urine  of  lactating  women,  and  occasionally 
in  the  urine  of  persons  on  an  exclusive  milk  diet.  It  gives  a  delayed 
and  incomplete  Fehling  test,  reduces  Nylander's  solution,  does  not 
ferment  with  yeast,  rotates  polarized  light  to  the  right.  While  it 
forms  a  yellow  osazone  with  phenyl-hydrazine,  the  amount  present  in 
the  urine  is  rarely  sufficient  to  give  a  positive  test. 

Pentoses,  C5H10O5,  occur  in  many  fruits  and  vegetables  as  complex 
carbohydrates,  known  as  pentosanes.  When  taken  into  the  body  the 
pentosanes  are  split  and  pentose  is  excreted  in  the  urine.  Consid- 
erable pentose  is  found  in  the  urine  of  persons  addicted  to  the  use 
of  morphine.  Pentoses  owe  their  chief  importance  to  the  similarity 
of  their  reactions  to  those  of  glucose.  Normally,  the  quantity  of 
pentose  in  the  urine  is  not  such  as  to  interfere  with  the  reactions  for 
sugar. 

Pentoses  reduce  Fehling's  and  bismuth  solutions ;  they  are  dextrorotatory ; 
with  phenyl-hydrazine  they  form  a  crystalline  compound,  melting  between 
153°  and  158°  C.  (307°  and  317°  F.).  Pentoses  do  not  ferment  with  yeast,  and 
are  characterized  by  responding  to  Tollen's  orcin  reaction.  This  is  made  by 
adding  3  c.c.  of  a  saturated  solution  of  orcin  in  hydrochloric  acid  to  5  c.c.  of 
urine  previously  decolorized  with  boneblack.  In  the  presence  of  pentose  a 
green  color  develops  on  heating,  beginning  at  the  top  and  gradually  extending 
through  the  mixture. 

Glycuronic  acid,  CHO.(CHOH)4.CO2H.  Glycuronic  acid  occurs 
in  normal  urine  in  minute  amount.  It  is  an  oxidation  product  of 
glucose,  and  is  usually  present  in  the  form  of  the  conjugated  glycu- 
ronates,  i.  e.,  glycuronic  acid  linked  to  aromatic  bodies  (phenol,  cresol, 
etc.).  It  is  increased  after  the  taking  of  camphor,  chloral,  menthol, 
and  other  substances,  which  produce  aromatic  substances  in  the  urine 


736  PHYSIOLOGICAL  CHEMISTRY. 

to  which  the  glycuronic  acid  is  linked.  The  amount  usually  present 
is  not  sufficient  to  reduce  Fehling's  solution,  unless  the  boiling  is  con- 
tinued for  a  long  time.  The  conjugate  glycuronates  are  Isevorotatory. 

Glycuronic  acid  reduces  Fehling's  and  bismuth  solutions,  forms  an  osazone 
melting  at  115°  C.  (239°  F.),  does  not  ferment  with  yeast,  and  is  dextrorotatory. 
5  c.c.  of  urine  containing  glycuronic  acid  when  decolorized  with  boneblack, 
mixed  with  an  equal  volume  of  hydrochloric  acid  and  0.025  phloroglucin,  de- 
velops a  deep-red  color  on  heating.  (This  reaction  is  also  shown  by  pentoses  ; 
glycilronic  acid  does  not  give  the  orcin  reaction.) 

Acetone,  diacetic  and  /3-oxy-butyric  acids.  These  substances, 
commonly  called  the  "  acetone  bodies/'  are  believed  to  be  due  to  an 
abnormal  metabolism  of  fat,  though  the  protein  metabolism  may  also 
be  concerned.  As  can  be  seen  from  the  following  reactions  acetone 
is  derived  from  diacetic  acid,  and  diacetic  acid  from  /9-oxy -butyric 
acid : 

CH3CH(OH).CH2.COOH  +  O  =  CH3.CO.CH2COOH  +  H2O 
/3-oxy-butyric  acid.  Diacetic  acid. 

CH3.CO.CH3.COOH  =  CH3.CO.CH3  -f  CO2 
Acetone. 

As  oxy-butyric  acid  and  diacetic  acid  are  unstable,  acetone  is  the 
first  of  these  bodies  to  appear  in  the  urine,  and  it  is  only  as  the 
pathological  conditions  increase  that  diacetic  and  finally  oxy-butyric 
acid  are  found.  Acetone  is,  indeed,  normally  present  in  minute 
amounts,  and  is  always  increased  in  the  presence  of  the  other  two. 
As  these  bodies  have  the  same  origin,  their  presence  has  the  same  sig- 
nificance, the  higher  members  showing  merely  a  graver  aspect. 

They  are  increased,  in  many  conditions  :  with  a  carbohydrate-free 
diet,  in  any  cachectic  condition,  in  many  types  of  fever.  They  are 
markedly  increased  in  diabetes. 

The  more  severe  cases  of  acetonuria  are  also  referred  to  as  acido- 
sis  (acid  intoxication).  The  term  emphasizes,  of  course,  not  the  acid 
excreted  in  the  urine,  but  the  acid  remaining  in  the  system.  In 
order  to  neutralize  this  abnormal  acidity  without  using  the  fixed 
alkali  of  the  body  the  organism  converts  less  nitrogen  into  urea 
than  is  normally  done,  and  uses  it  as  an  alkali  in  the  form  of  ammonia. 
Thus  the  proportion  of  the  urinary  nitrogen  in  the  form  of  ammonia 
is  increased  in  acidosis,  becoming  even  40  per  cent.,  the  normal  being 
5  or  6  per  cent.  This  percentage  is  the  best  index  of  the  severity  of 
the  condition. 

Acidosis  is  most  common  in  diabetes  and  pernicious  vomiting  of 
pregnancy,  and  indicates  the  danger  of  coma. 


URINE  AND   ITS  CONSTITUENTS.  737 

Legal's  test  for  acetone.  To  25  c.c.  of  urine  add  an  equal  volume  of  a  strong, 
freshly-made  solution  of  sodium  nitroprusside,  and  then  a  few  drops  of  sodium 
hydroxide  solution.  In  the  presence  of  acetone  a  red  color  develops,  which,  on 
addition  of  an  excess  of  acetic  acid,  becomes  darker  red.  (Compare  WeyPs 
reaction  for  creatinine.) 

Acetone  may  also  be  recognized  in  the  following  manner  :  500  c.c.  of  urine 
are  acidified  with  a  few  drops  of  hydrochloric  acid  and  distilled.  To  the  dis- 
tillate a  few  drops  of  iodine  solution  (1  iodine,  2  potassium  iodide,  100  water) 
and  of  potassium  hydroxide  are  added.  If  acetone  is  present,  a  characteristic 
yellowish- white  precipitate  of  iodoform  is  formed. 

Diacetic  acid  is  recognized  by  adding  to  the  urine  drop  by  drop  a 
fairly  strong  solution  of  ferric  chloride,  filtering  off  any  precipitate 
of  phosphate,  and  adding  more  ferric  chloride,  when  in  the  presence 
of  diacetic  acid  a  deep-red  color  is  produced,  which  disappears  on 
boiling.  The  test  should  also  be  made  with  an  ethereal  extract,  ob- 
tained by  shaking  urine  previously  acidified  with  sulphuric  acid  with 
ether ;  the  ferric  chloride  solution,  on  being  agitated  with  the  ethereal 
extract,  becomes  red.  (As  salicylic  acid  and  a  number  of  other  sub- 
stances give  a  red  or  violet  color  with  ferric  chloride,  care  must  be 
taken  not  to  confound  diacetic  acid  with  these  substances.) 

The  detection  of  /3-oxy-butyric  acid  is  difficult,  and  is  rarely  done 
in  clinical  work.  Its  presence  is  probable  when  urine,  after  being 
fermented,  still  contains  a  tavorotatory  body. 

Bile  may  be  present  in  the  urine  in  any  case  of  jaundice. 

Detection  of  bile-pigment.  The  presence  of  bile  in  urine  is  gen- 
erally indicated  by  a  decided  color,  which  varies  from  a  deep  brown- 
ish-red to  a  dark  brown  ;  the  foam  of  such  urine  (produced  by  shak- 
ing) has  a  distinct  yellow  color,  and  a  piece  of  filtering-paper  or  a 
piece  of  linen  dipped  into  the  urine  assumes  a  yellow  color,  which 
does  not  disappear  on  drying. 

The  further  detection  of  bile  depends  upon  the  reactions  of  the 
biliary  coloring-matters  or  biliary  acids. 

Tests  for  bile. 

1.  Gmelin's  test  for  biliary  coloring-matters  has  been  considered, 
and  may  be  applied  to  urine  either  by  allowing  a  small  quantity 
of  nitric  acid,  containing  some  nitrous  acid,  to  flow  down  the  sides 
of  a  test-tube  (containing  the  urine)  in  such  a  manner  that  the  two 
fluids  do  not  mix,  or  by  placing  upon  a  porcelain  plate  a  few  drops 
of  the  urine,  near  it  a  few  drops  of  nitric  acid,  to  which  one  drop  of 
sulphuric  acid  has  been  added,  and  allowing  the  two  liquids  to  ap- 
proach gradually.  In  both  cases  (if  bile-pigment  is  present)  a  play  of 

47 


738  PHYSIOLOGICAL   CHEMISTRY. 

color  is  seen  at  the  point  of  union  between  the  two  fluids,  the  colors 
changing  from  green  to  blue,  violet-red,  and  yellow  or  yellowish- 
green.  While  the  appearance  of  the  green  at  the  beginning  is  indis- 
pensable to  prove  the  presence  of  bile,  the  presence  of  all  the  other 
colors  is  not  essential.  (Plate  VIII.,  7.) 

The  above  test  may  be  made  in  a  somewhat  modified  form  by  mix- 
ing the  urine  with  a  concentrated  solution  of  sodium  nitrate,  and 
pouring  down  the  sides  of  the  test-tube  concentrated  sulphuric  acid  in 
such  a  manner  as  to  form  two  distinct  layers  ;  the  colors  are  seen  at 
the  point  of  contact  as  above. 

If  the  urine  be  very  dark  in  color,  it  should  be  diluted  with  water 
before  applying  the  above  tests. 

2.  Add  a  few  drops  of  sodium  carbonate  solution  to  the  urine  until 
it  has  a  distinct  alkaline  reaction,  then  add  calcium  chloride  and 
shake  well.  The  precipitated  calcium  carbonate  carries  down  the 
pigments  and  leaves  the  urine  nearly  colorless  or  of  its  normal  color. 
Collect  the  precipitate  on  a  filter,  wash,  and  transfer  it  with  alcohol 
to  a  test-tube.  Dissolve  by  the  addition  of  hydrochloric  acid  and 
boil  the  clear  solution,  when  it  turns  green.  Allow  to  cool  and  add 
nitric  acid,  when  the  green  solution  turns  blue,  violet,  and  red. 
(This  test  may  show  the  presence  of  biliary  coloring-matters  when 
Gmelin's  test  fails  to  do  so,  and  is  recommended  when  the  urine  con- 
tains a  large  amount  of  indican.) 

While  bile  acids  are  always  present  with  bile-pigment  in  urine, 
their  demonstration  is  usually  difficult. 

Pettenkofer's  test  for  biliary  acids  is  made  by  dissolving  a  few 
grains  of  cane-sugar  in  urine  contained  in  a  test-tube,  and  allowing 
concentrated  sulphuric  acid  to  trickle  down  the  side  of  the  inclined 
test-tube ;  a  purple  band  is  seen  at  the  upper  margin  of  the  acid,  and 
on  slightly  shaking  the  liquid  becomes  at  first  turbid,  then  clear,  and 
almost  simultaneously  it  turns  yellow,  then  pale  cherry-red,  dark 
carmine-red,  and  finally  a  beautiful  purple  violet.  The  temperature 
must  not  be  allowed  to  rise  much  above  38°  C.  (100°  F.). 

As  many  substances  (other  than  biliary  acids)  show  a  similar 
reaction,  it  is  often  necessary  to  separate  the  bile  acids  by  the  process 
described  in  connection  with  the  consideration  of  bile  itself. 

In  case  the  quantity  of  biliary  constituents  is  so  small  that  they 
cannot  be  noticed  by  the  tests  mentioned,  the  urine  should  be  shaken 
with  about  one-fourth  of  its  volume  of  chloroform,  which  dissolves 
the  biliary  matters.  Some  of  this  solution  is  dropped  upon  blotting 
paper,  and  after  evaporation  a  drop  of  red  fuming  nitric  acid  is 


PHYSIOLOGICAL   REACTIONS. 


PLATE  VIII. 


Xanthoproteic  Reaction. 


Biuret  Reaction.  Most  albumins  sho^ 
the  color  on  the  left,  peptones  that  on  th< 
right. 


Indican    Reaction. 


Murexid  Test  for  uric  acid. 


Fehling's  Test  for  sugar. 


6 


Botger's  bismuth  Test  for  sugar. 


Gmelin's    Test     for    biliary    colorin 
matters. 


8 


Diazo  Reaction. 


Affoen&Ca  Litti  Bultiinorf,  ,\td. 

For  explanation  of  reactions  see  page  in   Index. 


URINE  AND  ITS  CONSTITUENTS.  739 

placed  in  the  centre  of  the  remaining  stain,  when  concentric  color 
rings  appear.  The  second  portion  of  chloroform  solution  is  evap- 
orated and  the  residue  used  for  making  the  reactions,  as  described 
above. 

Melanin  (melanogen),  the  black  pigment  of  the  skin  of  the  negro,  has  been 
found  in  the  urine  of  persons  suffering  from  melanotic  cancer  and  certain  wast- 
ing diseases.  Urine  containing  melanin  darkens  on  standing,  turns  black  on 
the  addition  of  either  nitric  or  chromic  acid,  and  forms  with  bromine-water  a 
yellow  precipitate  rapidly  turning  dark. 

Alkaptonic  acids.  Two  of  these  acids  occur  in  the  urine  of  certain 
otherwise  healthy  persons,  and  seem  to  be  without  clinical  signifi- 
cance. The  acids  are  :  Jiomogentisic  acid,  dioxphenyl-acetic  acid, 
C6H3(OH)2.CH2.CO2H,  and  uroleucic  acid,  dioxyphenyl-lactic  acid, 
CGH3(OH)2.C2H3.OH.C02H. 

Both  acids  reduce  Fehling's  solution,  as  also  ammoniacal  silver  nitrate  solu- 
tion, but  not  bismuth  solution ;  they  are  optically  inactive,  do  not  form  an 
osazone,  and  do  not  ferment  with  yeast. 

To  test  for  alkaptonic  acids,  the  urine  should  be  acidified  with  hydrochloric 
acid  and  then  extracted  with  ether.  The  ethereal  solution  is  evaporated,  the 
residue  dissolved  in  water,  and  heated  with  Millon's  reagent.  In  the  presence 
of  alkaptonic  acids  a  purple-red  color  is  observed. 

Diazo-reaction.  Some  abnormal  constituent  (which  has  not  yet 
been  isolated)  is  found  in  the  urine  of  certain  diseases.  The  presence 
of  this  unknown  substance  is  indicated  by  a  very  characteristic  reac- 
tion with  diazo-benzene-sulphonic  acid,  which  compound  is  produced 
by  the  action  of  nitrous  acid  on  sulphanilic  acid.  Two  solutions  are 
required  :  a.  5  grammes  of  sulphanilic  acid  dissolved  in  a  mixture 
of  50  c.c.  of  hydrochloric  acid  and  1000  c.c.  of  water;  6.  a  0.5 
per  cent,  solution  of  sodium  nitrite.  To  perform  the  reaction  50 
parts  of  a  and  1  part  of  b  are  mixed,  and  equal  volumes  of  the  reagent 
and  of  urine  are  mixed  in  a  test-tube  and  saturated  with  ammonia. 
In  those  cases  in  which  the  reaction  is  positive  the  solution  assumes 
a  carmine-red  color,  which,  on  shaking,  must  also  be  visible  in  the 
foam.  If  the  test-tube  is  allowed  to  stand  twenty-four  hours,  a 
greenish  precipitate  is  formed.  Normal  urine,  thus  treated,  shows  a 
deep-yellow  or  orange  to  orange-red  color;  the  precipitated  phos- 
phates as  well  as  the  foam  are  colorless.  On  Plate  VIII.,  8,  the 
color  of  the  diazo-reaction  is  represented.  Normal  urine  may  show 
the  orange-red  on  the  left,  but  the  carmine-red  on  the  right  is  char- 
acteristic of  the  diazo-reaction. 

If,  instead  of  mixing  the  urine  and  reagent  with  ammonia  water, 


740  PHYSIOLOGICAL   CHEMISTRY. 

the  latter  be  allowed  to  float  on  the  mixture,  a  carmine-red  ring  will 
form  at  the  zone  of  contact,  when  the  reaction  is  positive. 

It  was  formerly  held  that  this  test  is  pathognomonic  of  typhoid 
fever.  Later  work  has,  however,  shown  that  it  usually  is  present  in 
typhoid  fever  and  measles  ;  it  is  frequently  present  in  erysipelas, 
pneumonia,  scarlet  fever,  diphtheria,  and  pulmonary  tuberculosis ;  it 
is  rarely  present  in  acute  rheumatic  fever  and  cerebrospinal  men- 
ingitis. 

It  is,  however,  of  much  value  in  the  diagnosis  of  typhoid  fever,  and 
is  thought  to  indicate  a  bad  prognosis  in  pulmonary  tuberculosis. 

Functional  tests  of  the  kidney.  Many  attempts  have  been  made 
to  find  a  substance  which,  when  injected  into  the  body,  would  be 
excreted  by  the  kidney  in  such  a  manner  that  examination  of  the 
urine  would  show  the  ability  of  the  kidneys  to  carry  on  their  func- 
tion of  excretion.  Among  the  substances  tried  are  methylene-blue, 
salicylic  acid,  and  phloridzin.  By  far  the  most  suitable  substance 
has  recently  been  found  in  phenolsulphonephthalein  (Geraghty- 
Rowntree).  This  substance  has  no  poisonous  action,  and  is  excreted 
very  rapidly  by  normal  kidneys.  It  produces  a  red  color  in  alkaline 
solution,  and  its  amount  may  thus  be  readily  estimated  by  noting  the 
extent  to  which  a  standard  solution  must  be  diluted  to  produce  the 
same  depth  of  color.  It  is  somewhat  more  accurate  to  use  a  special 
instrument,  a  colorimeter.  After  the  injection  of  this  drug  (0.006 
gramme)  the  unchanged  drug  will,  under  normal  conditions,  appear 
in  the  urine  in  from  five  to  eleven  minutes,  50  per  cent,  is  excreted 
during  the  first  hour,  and  from  60  to  80  per  cent,  during  the  first  and 
second  hour  together. 

In  diseases  of  the  kidneys  the  initial  appearance  is  delayed  and  the 
hourly  output  is  decreased. 

Urinary  deposits  (sediments).  Normal  urine  is  always  clear,  but 
occasionally,  and  particularly  in  abnormal  conditions,  it  is  turbid. 

Urine  may  be  turbid  when  passed,  and  this  indicates  an  excess 
of  mucus,  or  the  presence  of  renal  epithelium,  pus,  blood,  chyle, 
semen,  bile,  fat-globules,  or  phosphates  or  urate  of  sodium  in  excess, 
etc.  A  turbidity  subsequent  to  the  passage  of  the  urine  is  generally 
due  to  the  precipitation  of  phosphates  or  urates,  or  it  may  result 
from  fermentation  or  decomposition.  Either  of  the  substances  named 
will  form  a  deposit  on  standing. 

When  such  a  deposit  is  to  be  examined,  a  few  ounces  of  the  urine 
should  be  set  aside  for  several  hours  in  a  tall,  narrow,  cylindrical 


URINE  AND  ITS  CONSTITUENTS. 


741 


glass  or  whirled  in  the  centrifuge  for  a  few  minutes ;  when  the 
sediment  has  collected  at  the  bottom  the  supernatant  urine  may  !><> 
decanted,  or  the  sediment  may  be  taken  out  by  means  of  a  pipette 
for  examination. 

Sediments  are  either  organized  or  unorganized.  To  the  first 
belong:  mucus,  blood,  pus,  fat,  urinary  casts,  epithelium,  sprrmato- 
zoids,  fungi,  infusoria,  etc. ;  to  the  second  belong :  uric  acid,  urates, 
calcium  oxalate,  phosphate,  or  carbonate,  magnesium-ammonium 
phosphate,  cystine,  hippuric  acid,  etc. 

The  chemical  examination  of  any  urinary  sediment  should  always 
be  preceded  by  a  microscopical  examination,  which  latter  is  in  many 

FIG.  76. 


Various  forms  of  uric  acid  crystals.    (Finlayson.) 

cases  the  only  way  of  determining  the  nature  of  the  sediment,  espe- 
cially of  the  organized  substances. 

Organized  sediments.  Red  blood-corpuscles  appear  under  the 
microscope  as  reddish,  circular  disks,  sometimes  laid  together  in 
strings.  If  seen  in  profile,  they  appear  biconcave. 

Pus  cells  (leucocytes)  appear  as  round  granular  cells,  in  which  the 
nucleus  frequently  is  not  made  out  until  dilute  acetic  acid  is  added. 

Epithelial  cells,  from  the  urinary  tubules,  ureter,  bladder,  vagina, 
etc.  Their  place  of  origin  is  frequently  difficult  to  determine. 

Casts.  Hyaline,  waxy,  finely  granular,  coarsely  granular,  pus 
casts,  blood  casts,  epithelial  casts. 

Unorganized  sediments,  (a)  In  acid  urine.  Uric  acid  is  deposited 
in  colored  crystals  from  acid  urine ;  it  is  not  dissolved  by  heat,  nor 


742 


PHYSIOLOGICAL   CHEMISTRY. 


by  acetic  or  hydrochloric  acid,  but  dissolves  on  the  addition  of  caustic 
potash  and  burns  on  platinum  foil  without  leaving  a  residue ;  it  is 
recognized  by  the  murexide  test.  Uric  acid  crystallizes  in  many  forms, 
usually  in  rhombs  with  rounded  corners,  the  so-called  "whetstone 
crystals."  The  crystals  are  usually  brow7n.  The  sediment  has  a 

FIG.  77. 


Calcium  oxalate  crystals.     (Finlayson.) 


red  crystalline  appearance  ("  brick-dust  "),  and  occurs  in  any  concen- 
trated, strongly  acid  urine. 

Add  urates  (Na,  K)  form  a  voluminous  sediment,  amorphous  under 
the  microscope,  of  a  yellowish-brown  or  reddish  color.  This  is  the  only 
sediment  which  dissolves  on  heating. 


FIG.  78. 


Crystalline  phosphates.     (Finlayson.) 


Calcium  oxalate  is  rarely  found  in  more  than  microscopic  amounts. 
The  crystals  are  peculiarly  clear,  and  have  a  double  envelope,  or 
sometimes  a  dumb-bell  appearance. 

Magnesium-ammonium  phosphate,  or  triple  phosphate,  MgNH4.- 
PO4.6H2O,  is  found  generally  in  triangular  prisms  with  bevelled. 


URINE  AND  ITU  CONSTITUENTS. 


743 


ends,  but  sometimes  also  in  star-shaped,  feathery  crystals,  due  to  the 
partial  dissolving  of  the  first  type.  These  crystals  are  most  abundant 
in  alkaline  urine,  but  are  also  present  in  faintly  acid  urines.  They 
dissolve  in  acetic  acid. 

(b)  In  alkaline  urine.  Ammonium-magnesium  phosphate  (vide  supra). 

FIG.  79. 


Ammonium  urate  crystals.     (C.  E.  Simon.) 


Calcium  and  magnesium  phosphates.  These  are  basic  phosphates. 
They  form  the  commonest  sediment  in  alkaline  urine,  are  amorphous, 
dissolve  with  acetic  acid,  but  not  with  heat. 


FIG.  80. 


y-© 


Crystals  of  leucine  (different  forms).  (Crystals  of  creatinine-zinc  chloride  resemble  the 
leucine  crystals  depicted  at  a.)  The  crystals  figured  to  the  right  consist  of  comparativelj 
impure  leucine.  (Charles.) 

(c)  In  ammoniacal  urine.     Ammonium-magnesium  phosphate  (vide 

supra). 

Ammonium  urate  is  found,  generally  associated  with  amorphous  or 
crystalline  phosphates,  in  urine  which  has  become  ammoniacal. 
crystalline  globules  are  generally  covered  with  spinous  excrescences, 
which  give  them  the  characteristic  "thorn-apple"  appearance,  and 
have  a  yellow  color.     They  are  soluble  in  acetic  acid. 


744 


PHYSIOLOGICAL   CHEMISTRY. 


The  following  crystals  occur  only  in  abnormal  urines : 
Leucine,    or    amino-caproic    acid,    C6Hn(XH2)O2,    and    Tyrosine, 
C9HUNO3,  are  but  rarely  met  with  in  urinary  deposits.     Leucine  is 
found  either  as  rounded  lumps,  showing  but  little  crystalline  structure, 


FIG.  81. 


Tyrosine  crystals.    (Charles.) 


or  as  spherical  masses,  exhibiting  fine  radial  striation.  Tyrosine 
appears  generally  in  fine,  long,  silky  needles,  forming  bundles  or 
rosettes. 

Cystine  occurs  occasionally  as  a  grayish,  crystalline  deposit,  form- 


FIG.  82. 


Crystals  of  cystine  spontaneously  voided  with  urine.     (Roberts.) 

ing  transparent  six-sided  plates ;  it  also  occurs  in  calculi.  The  latter 
may  be  recognized  by  the  chemical  properties  mentioned  below,  or  by 
dissolving  a  little  in  hydrochloric  acid  and  neutralizing  with  ammonia, 
when  cystine  is  reprecipitated  and  shows  the  characteristic  six-sided 
plates  under  the  microscope. 


URINE  AND  ITS  CONSTITUENTS.  745 

Urinary  calculi  are  solid  deposits  of  various  sizes  formed  from 
the  urine  within  the  kidney,  ureter,  bladder,  and  urethra.  They 
may  contain  all  the  constituents  of  urine  which  occur  as  sediments, 
and  also  certain  pathological  constituents  deposited  around  an  organic 
framework. 

Calculi  are  cal led  primary  when  formed  in  unchanged  urine,  and  secondary 
when  they  are  formed  in  urine  which  has  undergone  decomposition.  Uric 
acid,  calcium  oxalate,  calcium  carbonate,  xanthine,  and  cystic  calculi  are 
primary  formations,  while  ammonium  urate,  phosphatic  and  urostealith  calculi 
3,re  secondary. 

During  the  development  of  a  calculus  the  original  deposit  may  be  covered 
by  a  layer  of  a  different  material,  which  in  turn  may  be  covered  by  another 
substance.  For  this  reason  a  simple  stone  may  be  converted  into  a  compound 
one.  In  this  way  a  primary  stone,  by  irritation  of  the  bladder  producing 
cystitis,  accompanied  by  alkaline  fermentation,  causes  a  deposition  of  phos- 
phates, and  is  converted  into  a  secondary  calculus.  The  further  action  of  the 
alkaline  urine  may  dissolve  the  primary  calculus,  replacing  it  with  phosphates. 

In  examining  calculi  it  is  necessary  to  make  a  section  through  the 
centre  of  the  calculus  and  scrape  off  a  little  from  each  layer,  the 
portions  being  examined  separately.  They  may  be  found  to  be  alike 
(simple  calculi)  or  unlike  (compound  or  mixed  calculi)  in  composi- 
tion. The  following  scheme  serves  for  a  qualitative  examination  of 
calculi.  Heat  some  of  the  powdered  calculus  on  platinum  foil,  when 
the  material  will  either  burn  and  char  without  a  flame  (A),  or  burn 
with  a  flame  (B),  or  will  not  burn  at  all  (C).  (It  should  be  remem- 
bered that  a  calculus  generally  contains  a  little  organic  matter,  so  that 
slight  carbonization  is  always  to  be  expected  on  heating  it.) 

A.  To  the  material    burning  without  a  distinct   flame  apply  the 
murexide  test.     If  affirmative,  uric    acid    or  urates  are    indicated. 
Heat  some  powder  with  potassium  hydroxide;   a   strong   odor  of 
ammonia  proves  the  calculus  to  consist  of  ammonium  urate;  a  nega- 
tive result  shows  it  to  be  uric  acid.     If  the  murexide  test  was  nega- 
tive,   test    for   xanthine.     The    powder  wall    dissolve  in  nitric  acid 
without  effervescence,  leave  on  evaporation  a  yellow  residue,  turning 
orange  with  alkali  and  red  on  heating. 

B.  Material  burning  with   a  distinct  flame  may  either  be  soluble 
in  alcohol  and  ether  (urostealith)  or  insoluble  in  these  solvents,  but 
soluble  in  potassium  hydroxide  solution  on  heating  (fibrin),  or  soluble 
both  in  hydrochloric  acid  and  in  caustic  alkalies  (cystine).      Urostea- 
lith burns  with  a  yellow  flame  and  emits  the  odor  of  burning  resin. 
Fibrin  burns   also  with  a  yellow  flame,    but  emits   odor   of  burnt 
feathers.     Cystine  burns  with  a  pale-blue  flame,  emitting  a  peculiar 


746  PHYSTOLOGICAL  CHEMISTRY. 

sharp  odor.  On  evaporation  of  its  solution  in  ammonia  it  separates 
in  characteristic  six-sided  plates. 

C.  Material  which  does  not  burn  may  consist  of  calcium  car- 
bonate, calcium  oxalate,  or  phosphates.  Calcium  carbonate  shows 
effervescence  with  all  acids,  and  the  solution,  after  being  neutralized, 
is  precipitated  by  ammonium  oxalate.  Calcium  oxalate  does  not 
effervesce  with  hydrochloric  acid  directly,  but  does  so  after  being 
heated,  when  carbonate  is  formed  and  is  tested  for  as  such.  The 
presence  of  phosphates  is  indicated  by  the  presence  of  a  yellow  pre- 
cipitate, produced  in  the  solution  in  nitric  acid  by  ammonium  molyb- 
date.  When  the  phosphates,  on  heating  with  caustic  potash,  evolve 
ammonia  gas,  magnesium  ammonium  phosphate  is  present ;  when  the 
test  is  negative  the  calculus  consists  of  calcium  phosphate,  which  can 
be  verified  by  dissolving  the  powder  in  hydrochloric  acid,  neutral- 
izing with  ammonia,  redissolving  the  precipitate  in  acetic  acid,  and 
adding  ammonium  oxalate,  when  a  white  precipitate  is  formed. 

Most  common  are  calculi  of  uric  acid  ;  often  met  with  are  those  of 
urates,  phosphates,  and  oxalates ;  rarely,  however,  those  of  xanthine, 
cystine,  fibrin,  and  urostealith. 

QUESTIONS. — What  is  urine,  where  and  by  what  process  is  it  formed  in  the 
animal  body,  and  what  is  its  function?  Mention  the  general  physical  and 
chemical  properties  of  urine.  Give  the  composition  of  human  urine,  and  state 
by  what  conditions  the  composition  is  influenced.  State  the  composition  and 
properties  of  urea.  By  what  process  is  urea  formed  in  the  animal  body,  and 
how  can  it  be  obtained  artificially  ?  Describe  a  process  by  which  urea  may  be 
estimated  quantitatively  in  urine.  In  what  forms  is  uric  acid  found  in  urine, 
and  what  are  its  properties?  Describe  the  murexide  test.  How  can  uric  acid 
be  determined  quantitatively  in  urine?  What  is  hippuric  acid,  and  by  what 
tests  may  it  be  recognized  ?  What  points  are  to  be  considered,  and  what  sub- 
stances determined,  in  the  analysis  of  normal  and  abnormal  urine?  What  is 
the  color  of  urine,  and  what  are  the  chief  causes  influencing  the  color  ?  What 
is  the  specific  gravity  of  healthy  urine,  how  is  it  determined,  and  how  is  the 
total  amount  of  solids  approximately  calculated  from  the  specific  gravity? 
Describe  the  different  tests  by  which  albumin  may  be  recognized,  and  state  the 
precautions  necessary  in  making  these  tests.  How  may  the  quantity  of  al- 
bumin in  urine  be  determined  approximately,  and  also  accurately?  Describe 
the  various  tests  for  sugar.  On  what  principles  are  they  based,  and  how  can 
sugar  be  distinguished  from  other  reducing  substances  occurring  in  urine? 
How  is  sugar  determined  quantitatively  ?  By  what  tests  are  biliary  pigments 
and  acids  recognized  in  urine?  What  is  the  nature  of  urinary  sediments,  and 
by  what  means  are  they  recognized?  What  are  urinary  calculi  generally  com- 
posed of,  and  by  what  simple  tests  can  their  nature  be  determined? 


APPENDIX. 


TABLE  OF  WEIGHTS  AND  MEASURES. 


Measures  of  length. 


1 

millimeter 

= 

0.001 

meter 

=      0.0393/ 

1 

centimeter 

— 

0.01 

meter 

=      0.3937 

1  decimeter     — 

0.1 

meter 

=      3.937 

1 

meter 

=    39.37 

1 

decameter 

= 

10 

meters 

=    32.8083 

1 

hectometer 

= 

100 

meters 

=  328.083 

1 

kilometer 

r=r 

1000 

meters 

=      0.6213' 

1 

1 

yard  or  36 
inch 

inches 

=      0.9144 
=     25.4 

inch. 

inches. 

inches. 

feet. 

feet. 

mile. 

meter. 

millimeters. 


1  milliliter 
1  centiliter 
1  deciliter 
1  liter 
1  decaliter 
1  hectoliter 
1  kiloliter 
1  U.  S.  gallon 
1  imperial  gallon 
1  minim 
1  fluidrachm 
1  fluidounce 
1  liter 


Measures  of  capacity. 

1  c.c.  ==  0.001  liter  = 

10  c.c.  =•  0.01  liter  = 

100  c.c.  =  0.1  liter  = 
1000c.c. 

=  10  liters  = 

=  100  liters  = 

=  1000  liters  = 


0.0021 
0.0211 
0.2113 
1.0567 
2.6417 
26.417 
264.17 
3785.43 
4543.5 
0.06 
3.70 
29.57 
33.81 


U.  S.  pint. 

U.  S.  pint 

U.  S  pint. 

U.  8.  quart. 

U.  S.  gallons. 

U.  S.  gallons. 

U.  S.  gallons. 

c.c. 

c.c. 

c.c. 

c.c. 

c.c. 

fluidounces. 


Weights. 


1  milligram 

= 

0.001 

gramme 

1  centigram 

= 

0.01 

gramme 

1  decigram 

= 

01 

gramme 

1  gramme 

1  decagram 

= 

10 

grammes 

1  hectogram 

= 

100 

grammes 

1  kilogram 

=. 

1000 

grammes 

1  kilogram 

1  grain  Troy 

1  drachm  Troy 

1  ounce  Troy 

1  ounce  avoirdupois 

1  pound  avoirdupois 

0.015  grain 

0.154  grain 

1.543  grain 

15.432  grains 

154.324  grains 

0.268  pound   Troy. 
2.679  pounds  Troy. 
2.2046  pounds  avoirdupois. 
0.0648  gramme. 
3.888    grammes. 
31.103    grammes. 
28.350    grammes. 
453.592    grammes. 

(747) 


748  APPENDIX. 

Commercial  weights  and  measures  of  the  U.  £  A. 

1  pound  avoirdupois  =     16     ounces. 

1  ounce  =  437.5  grains. 

1  gallon  =  231     cubic  inches. 

1  gallon  =      4     quarts  =  8  pints. 

1  pint  of  water  weighs  7291.2  grains  at  a  temperature  of  15.6°. 

Apothecarie^  weights. 

The  apothecaries'  ounce  is  of  the  same  value  as  the  now  obsolete  English  Troy 
ounce. 

1  ounce  8  drachms                                    480  grains. 

1  drachm  3  scruples                                      60  grains. 

1  scruple  20  grains. 

1  ounce  31.103  grammes. 

1  grain  64.799  milligrams. 

Apothecaries'  fluid  measures. 

These  are  derived  from  the  U.  S.  gallon  ;  the  liquid  pint  of  this  gallon  is  identical 
in  value  with  the  apothecaries'  pint. 

1  pint  16  fluidounces  7680  minims. 

1  fluidounce          =  8  fluidrachms  480  minims. 

1  fluidrachm  60  minims. 

Jewelers'  weight. 
1  carat  =  0.205  gramme  3.163  grains. 


TABLE  OF  ELEMENTS  AND  ATOMIC  WEIGHTS. 

On  the  basis  H^=  1  (U.  S.  P.,  VIII.)  and  O  =  16  (International  \\Vights,  1912). 


Name. 

Atomic  weights. 
Symbol.     H==1        Q==16 

Name.               Symbol 

Atomic  weights. 
H  =  1         0  =  16 

Aluminum 

.    .  Al 

26.9 

27.1 

Neodymium  .    . 

.Nd 

142.5 

144.3 

Antimony  .    . 

.    .  Sb 

119.3 

120.2 

Neon   

.  Ne 

19.9 

20.2 

Argon      .    .    . 

A 

39.6 

39.88 

Nickel 

Ni 

58.3 

58.68 

Arsenic  .    .    . 

.    .  As 

74.4 

74.96 

Nitrogen     .    .    . 

.N 

13.93 

14.07 

Barium  . 

Ba 

136.4 

137.37 

Osmium 

Os 

189.6 

ion  q 

Bismuth      .    . 

.    .  Bi 

206.9 

208 

Oxygen  .... 

.O 

15.88 

1  *7U.  »7 

16 

Boron 

B 

10.9 

]1 

"P?i  1  1  Q  f\  i  n  m 

Pd 

10^  7 

lOfi  7 

Bromine     .    . 

.    .  Br 

79.36 

79.92 

i  .1  1  i.u  1  1  1  in  i 

Phosphorus    .    . 

•    JTil 

.  P 

J.UO.  t 

30.77 

-lUv).  / 

31.04 

Cadmium    .    . 

.    .  Cd 

111.6 

112.4 

Platinum    .    .    . 

.Pt 

193.3 

195.2 

Caesium  .    .    . 

.    .  Cs 

131.9 

132.81 

Potassium  .    .    . 

.  K 

38.86 

39.1 

Calcium      .    . 

.    .  Ca 

39.8 

40.07 

Praseodymium3 

.  Pr 

139.4 

143.6 

Carbon    .    .    . 

.    .  C 

11.91 

12 

Radium  .... 

.  Ra 

223 

226.4 

Cerium  .    .    . 

.    .  Ce 

139.2 

140.25 

Rhodium    .    .    . 

.Rh 

102.2 

102.9 

Chlorine     .    . 

.    .  Cl 

35.18 

35.46 

Rubidium  .    .    . 

.Kb 

84.8 

85.45 

Chromium 

.    .  Cr 

51.7 

52 

Ruthenium     .    . 

.Ru 

100.9 

101.7 

Cobalt     .    .    . 

.    .  Co 

58.56 

58.97 

Samarium  .    .    . 

.Sm 

148.9 

150.4 

Columbium1  . 

.    .  Cb 

93.3 

93.5 

Scandium   .    .    . 

.80 

43.8 

44.1 

Copper   .    .    . 

.    .  Cu 

63.1 

63.57 

Selenium    .    .    . 

.  8e 

78.6 

79.2 

Erbium 

Er 

164.8 

167.7 

Silicon    .... 

.  Si 

28.2 

28.3 

J;  luorine 

F 

18.9 

19 

Silver 

As 

107.12 

107.88 

Gadolinium 

•        •     17 

.    .  Gd 

155.8 

157.3 

Sodium   .... 

'  -"o 

.Na 

22.88 

23 

Gallium      .    . 

.    .  Ga 

69.5 

69.9 

Strontium  .    .    . 

.Sr 

86.94 

87.63 

Germanium    . 

.    -  Ge 

71.9 

72.5 

Sulphur  .... 

.S 

31.83 

32.07 

Glucinum2     . 

.    .  Gl 

9.03 

9.1 

Tantalum   .    .    . 

.  Ta 

181.6 

181.5 

Gold    .... 

.    .  Au 

195.7 

197.2 

Tellurium  .    .    . 

.Te 

126.6 

127.5 

Helium  -    .    . 

.    .He 

3.99 

3.99 

Terbium     .    .    . 

.Tb 

158.8 

159.2 

Hydrogen  .    . 

.    .  H 

1.00 

1.008 

Thallium    .    .    . 

.  Tl 

202.6 

204 

Indium    .    .    . 

.    .  In 

113.1 

114.8 

Thorium     .    .    . 

.  Th 

230.8 

232.4 

Iodine 

I 

125.9 

126.92 

Thulium     .    . 

.Tm 

169.7 

168.5 

Iridium  . 

Tr 

mK 

1Q<J  1 

Tin      

.  Sn 

118.1 

119 

Iron     .... 

.  ir 
.    .  Fe 

.O 

55.5 

-L«/O.  i. 

55.84 

Titanium    .    .    . 

.Ti 

47.7 

48.1 

Krypton     .    . 

.    .  Kr 

81.2 

82.92 

Tungsten    .    .    . 

.  W 

182.6 

184 

Lanthanum    . 

.    .  La 

137.9 

139 

Uranium    .    .    . 

.U 

236.7 

238.5 

Lead    .... 

.    .  Pb 

205.35 

207.1        Vanadium  . 

.  V 

50.8 

51 

Lithium  .    .    . 

.    .  Li 

6.98 

6.94      Xenon     . 

.  Xe 

127 

130.2 

Magnesium    . 

•    •  Mg 

24.18 

24.32 

Ytterbium  .    . 

.  Yb 

171.7 

172 

Manganese 

.  Mn 

54.6 

54.93 

Yttrium  .... 

.  Yt 

88.3 

89 

Mercury     .    . 

Hg 

198.5 

200.6 

Zinc     

.  Zn 

64.9 

65.87 

Molybdenum 

.    .  Mo 

95.3 

96 

Zirconium  .    .    . 

.  Zr 

89.9 

90.6 

1  Also  called  Niobium, 

Nb.       2  Also  called  Beryllium,  Be.       3  Also  called  Didymium,  Di. 

749 


INDEX. 


A. 

ABSOLUTE  temperature,  47 

weight,  32 

zero,  48 
Absorption,  676,  687,  689 

by  charcoal,  39 

by  liquids,  39 

by  solids,  40 

spectra,  61 
Acacia,  536 
Accumulator,  320 
Acetanilide,  565 
Acetates,  503 
Acetic  aldehyde,  491 

anhydride,  505 

ether,  522 
Acetone,  494 

in  urine,  736 
Aceto-nitrile,  555 
Acetoximes,  541 
Acetphenetidin,  572 
Acetyl  chloride,  505 

oxide,  505 
Acetylene,  473 
Acid,  abietic,  599 

acetic,  500 

glacial,  501 

mono-,  di-,  and  trichlor-,  504 

acetyl-salicylic,  584 

acrylic,  494 

amino-acetic,  544 

ammo-formic,  545 

amino-succinamic,  543,  546 

amino-succinic,  543 

anisic,  585 

arabic,  536 

arsenic,  349 

arsenous,  348 

aspartic,  546 

barbituric,  547 

benzoic,  579,  701 

beta-oxybutyric,  736 

boric  or  boracic,  187,  701 

bromic,  240 

butyric,  505 

cacodylic,  478 

camphoric,  599 

carbamic,  269,  545 

carbazotic,  572 

carbolic,  569 

carbonic,  180 

chloric,  237 


Acid,  chlorpplatinic,  235,  367 
chromic,  308 
citric,  516 
cyanic,  553 
diacetic,  736 
dichromic,  308 
digallic,  586 
disulphuric,  212 
ethyl-sulphuric,  521 
formic,  500 
fulminic,  541 
galactonic,  532 
gallic,  586 
glacial  acetic,  501 

phosphoric,  226 
gluconic,  531 

glycerin-phosphoric,  448,  670 
glycocholic,  685 
glycolic,  511 
glycuronic,  735 
hippuric,  717 
homogentisic,  739 
hydrazoic,  170 
hydriodic,  242 
hydrobromic,  239 
hydrochloric,  232 
hydrocyanic,  548 
hydroferricyanic,  554 
hydroferrocyanic,  554 
hydrofluoric,  244 
hydrofluosilicic,  186 
hydroxy-acetic,  511 
hydroxy-propionic,  511 
hypobromous,  240 
hypochlorous,  236 
hyponitrous,  173 
hypophosphorous,  223 
hyposulphurous,  213 
indoxyl-sulphuric,  721 
iodic,  243 
lactic,  511 
malic,  512 
malonic,  508 
manganic,  303 
meconic,  615 
metaboric,  187 
metaphosphoric,  226 
met-arsenic,  349 
met-arsenous,  348 
meta-stannic,  363 
molybdic,  368 
mucic,  532 
muriatic,  232 

751 


752 


INDEX. 


Acid,  myronic,  556 
naphthionic,  590 
naphthylamine  sulphonic,  590 
nicotinic,  593 
nitric,  174 

ionic  explanation  of  liberation 

of,  195 

nitro-hydrochloric,  235 
nitro-muriatic,  235 
nitrosyl-sulphuric,  209 
nitrous,  173 

estimation  by  metaphenylene- 

diamine,  432 
oleic,  506 
oxalic,  508 
palmitic,  506 
parabanic,  547 
perchloric,  238 
perchromic,  310 
permanganic,  303,  305 
persulphuric,  214 
phenolsulphonic,  573 
phosphocarnic,  668 
phospho-molybdic,  601 
phosphoric,  226 
phosphorous,  225 
phthalic,  581 
picric,  572 
prussic,  548 
pyrogallic,  576 
pyrophosphoric,  226 
pyrosulphuric,  212 
pyrotartaric,  508 
racemic,  513 
rosolic,  410 
saccharic,  531 
salicylic,  583,  701 
salts,  definition  of,  122 
santonic,  590 
sarcolactic,  511,  669 
silicic,  186 
sozolic,  573 
stannic,  362 
stearic,  506 
succinic,  508 
sulphanilic,  566 
sulphocarbolic,  573 
sulphocyanic,  553 
sulpho-vinic,  521 
sulphuric,  208 
sulphurous,  206 
tannic,  586 
tartaric,  512 

isomerism  of,  513 
tauro-cholic,  685 
tetraboric,  187 
thiosulphuric,  213 
triazoic,  170 
trichlor-acetic,  504 
uric,  715,  741 

estimation  of,  716 
uroleucic,  739 
valeric,  505 
Acidic  oxides,  117 


Acidimetry,  412 

Acids,  activity  or  strength  of,  200 

alkaptonic,  739 
amino-,  544 
aromatic,  579 
definition  of,  117 
detection  of,  391 

dissociation  theory  applied  to,  199 
fatty,  496 

monobasic,  496 

hydroxy-,  organic,  510 

ions  formed  by,  200 

thio-,  212 
Aconitine,  617 
Acrolein,  493 

phenyl,  578 
Acrylic  aldehyde,  493 
Actinic  waves,  56 
Actinium,  84 
Action,  catalytic,  154 

contact,  154 

endothermic,  91 

exothermic,  91 

reversible,  114 
Activators,  638 
Activity,  optical,  67 
Adamkiewicz's  reaction,  627 
Adhesion,  37 
Adrenalin,  670 
Affinity,  chemical,  92 
After-damp,  184 
Agglutinins,  660 
Agucarine,  581 
Air,  analysis  of,  166 

expired,  182 

liquefaction  of,  166 
Alabaster,  277 

Albumin,  tests  for,  in  urine,  726 
Albuminoids,  628 
Albuminometer,  Esbach's,  726 
Albumins,  627 
Alcohol,  482 

absolute,  483 

allyl,  486 

amyl,  486 

benzyl,  577 

denatured,  485 

diluted,  483 

ethyl,  482 

methyl,  482 

salicylic,  584 
Alcoholic  liquors,  485 
Alcoholometers,  34 
Alcohols,  479 

aromatic,  577 

primary,    secondary,  and  tertiary, 
479 

sulpho-,  495 

thio-,  495 
Aldehyde,  acetic,  491 

acrylic,  493 

benzoic,  577 

cinnamic,  578 

formic,  490 


INDEX. 


753 


Aldehyde,  methylprotocatechuic,  578 
Aldehydes,  489 

aromatic,  577 
Aldoses,  530 
Aldoximes,  541 
Alkali-metals,  remarks  on,  255 

summary  of  tests,  272 
Alkalimeter,  34 
Alkalimetry,  412 
Alkaline-earth  metals,  277 

summary  of  tests,  285 
Alkaloids,  600 

antidotes  for,  602 

cadaveric,  617 

classification,  603 

detection  of,  in  poisoning,  602 
Alkyl,  definition  of,  474 
Alkylene,  definition  of,  474 
Allantoin,  717 
Allotropic  modifications,  129 

silver,  331 
Allotropy,  129 
Alloxur  bases,  667 
Alloys,  253,  323 

aluminum,  286 

antimony,  358 

arsenic,  347 

bismuth,  327 

copper,  323 

dental,  254,  337 

gold,  366 

iron,  294 

lead,  319 

manganese,  303 

manufacture  of,  254 

platinum,  367 

pot-metal,  254 

properties  of,  254 

silver,  331 

tin,  323 

zinc,  313,  323 
Allyl  alcohol, .  486 

iodide,  486 

isosulphocyanate,  556 

mustard  oil,  557 

sulphide,  557 

thio-urea,  557 
Alpha-derivatives,  588,  624 

-naphthol,  589 

-naphthylamine,  589 
Alum,  ammpnio-ferric,  299 

ammonium,  287 

burnt,  287 

chrome,  310 

definition  of  an,  286 

iron,  299 

potassium,  287 
Alumina,  287 
Aluminates,  288 
Aluminum,  285 

acetate,  287 

alloys  of,  286 

and  ammonium  sulphate,  287 

and  potassium  sulphate,  287 

48 


Aluminum-bronze,  286 

carbide,  466 

chloride,  289 

hydroxide,  287 

oxide,  286,  288 

silicate,  289 

sulphate,  288 
Alypin,  607 
Amalgams,  253,  337 

dental,  337 
Amber,  599 
Amboceptors,  661 
Amides,  543 
Amine,  di-  and  triethyl-,  620 

di-  and  trimethyl-,  620 

diphenyl-,  566 

ethyl,  620 

isoamyl,  620 

methyl,  620 

propyl,  620 
Amines,  541 

primary,  secondary,  and  tertiary, 

542 

Amino-acids,  544 
Aminoform,  543 
Ammeter,  77 
Ammonia,  167 

albuminoid,  431 

aromatic  spirit  of,  269 

determination    by    Nessler's  solu- 
tion, 431 

from  atmospheric  nitrogen,  553 

in  urine,  714 

ionic  explanation  of  liberation  of, 
194 

liniment,  526 

water,  169 
Ammonium,  268 

acetate,  503 

acid  urate,  743 

-amalgam,  268 

benzoate,  580 

bromide,  270 

carbamate,  269 

carbonate,  269 

chloride,  269 

hydrogen  sulphide,  270 

hydroxide,  169 

iodide,  270 

molybdate,  368 

nitrate,  270 

persulphate,  214 

phosphate,  270 

salicylate,  583 

sesquicarbona '?,  269 

sulphate,  270 

sulphide,  270 

sulphydrate,  270 

urate,  743 

valerate,  506 
Amorphism,  21 
Ampere,  77 
Amperemeter,  77 
Amphoteric  reaction,  707 


754 


INDEX. 


Amygdalin,  578 
Amyl  alcohol,  486 

nitrite,  523 
Amylases,  637 
Amylene,  472 

hydrate,  486 
Amyloid,  537,  630 
Amylopsin,  682 
Analysis,  151 

of  air,  166 

definition  of,  371 

gas,  427 

gravimetric,  402 

milk,  701 

proximate,  443 

qualitative,  371 

of  organic  compounds,  442 

quantitative,  371,  402 

spectroscopic,  62 

ultimate  or  elementary,  of  organic 
compounds,  442 

volumetric,  402 

water,  429 
Analytical  chemistry,  371 

reactions.     See  Tests. 

ionic  explanation  of,  200 
Anesthesin,  580 
Anethol,  584 
Anhydride  of  acids,  117,  141 

acetic,  505 

arsenic,  349 

arsenous,  348 

chromic,  308 

phthalic,  581 

Anhydrous,  definition  of,  152 
Aniline,  564 

-blue,  566 

dyes,  564 
Animal  charcoal,  280 

fluids  and  tissues,  649 

food,  641 
Anions,  190 
Annealing,  252 
Annidalin,  575 
Anode,  75,  190 
Antibodies,  660 
Antidiabetin,  581 
Antidotes  to  acetic  acid,  502 

alkalies,  257 

alkaloids,  602 

antimony,  361 

arsenic,  358 

barium,  284 

copper,  326 

hydrochloric  acid,  233 

hydrocyanic  acid  and  its  salts,  552 

hydrogen  sulphide,  214 

lead,  322 

mercury,  345 

nitric  acid,  177 

oxalic  acid,  509 

phenol,  571 

phosphorus,  222 

silver,  334 


Antidotes  sulphuric  acid,  212 

zinc,  317 
Antifebrin,  565 
Antigen,  661 
Antimonites,  359 
Antimony,  358 

alloys,  358 

and  potassium  tartrate,  361,  515 

black,  358 

butter  of,  360 

chlorides,  360 

crude,  358 

golden  sulphuret  of,  360 

oxides,  359 

oxychloride,  360 

spots,  difference  from  arsenic,  357 

sulphides,  359 

sulpho-salts,  359 
Antimonyl  chloride,  360 
Antipyrine,  591 

derivatives,  592 

incompatibles,  592 

isonitroso,  592 
Antiseptics,  457 
i  Antitoxin,  661 
|  Apatite,  219 
I  Apomorphine,  613 
Apparatus  for  qualitative  analysis,  371 

quantitative  analysis,  403-407 
Apparent  weight,  32 
Aqua  fortis,  174 

regia,  235 
Argentum,  330 

Crede,  331 
Argol,  512 
Argon,  166 
Argonin,  334 
Argyrol,  334 
Aristol,  575 
Armature,  74,  78 
Aromatic  acids,  579 

alcohols,  577 

aldehydes,  577 

compounds,  557 

containing  arsenic  and  phos- 
phorus, 568 
difference  from  fatty,  558,  561 

hydroxy-acids,  583 
Arsenetted  hydrogen,  350 
Arsenic,  346 

alloys  of,  347 

chloride,  347 

detection  in  cases  of  poisoning,  357 

group  of  metals,  remarks  on,  346 
summary  of  tests,  368 

and  mercury  iodide,  351 

pentoxide,  349 

spots     distinguished     from      anti- 
mony, 357 

sulphides,  347,  350 

trioxide,  348 
Arsenobenzene,  568 
Arsenous  anhydride,  348 

iodide,  351 


INDEX. 


755 


Arsenous  oxide,  348 
Arsine,  350 
Artiads,  104 
Asbestos,  272 
Asepsis,  458 
Aseptol,  573 
Asparagine,  546 
Asphalt,  599 
Aspirin,  584 
Atmospheric  air,  165 

pressure,  36 
Atomic  theory,  Dalton's,  96 

weight,  definition,  98 

determination  of,  105 
Atomicity,  103 
Atoms,  definition,  98 
Atoxyl,  568 
Atropine,  605 
Attraction,  capillary,  37 

molecular,  19 
Auric  chloride,  366 
Auripigment,  347 
Avogadro's  law,  30 
Azo  compounds,  567 

dyes,  567 

B. 

BABBIT-METAL,  323 
Bacillus  bulgaricus,  700 
Baking-powders,  264 

-soda,  264 
Balsam,  599 

copaiva,  599 
Barite,  283 
Barium,  283 

carbonate,  283 

chloride,  283 

cyanide  from  barium  carbide,  553 

dioxide,  283 

nitrate,  284 

oxide,  283 

platinocyanide,  368 

sulphate,  283 
Barley  sugar,  533 
Barometer,  34 
Basalt,  286 
Bases,  activity  of,  201 

definition  of,  118 

dissociation     theory     applied     to, 
200 

organic,  541 

Basic  salts,  definition  of,  122 
Battery,  storage,  320 
B<  inuerel  rays,  84 
Beer,  486 
Beet-sugar,  533 
Bell-metal,  323 

Bence-Jones  body  in  urine,  727 
Benzaldehyde,  577 
Benzene,  562 

diamino-,  566 

nitro-,  563 

series  of  hydrocarbons,  562 


Benzene  theory,  558 
Benzin,  468 
Benzol,  562 

hexahydroxy-,  532 
Benzosulphinide,  580 
Benzoyl  chloride,  580 

-ecgonine,  606 

-naphthol,  589 
Benzoylation,  580 
Benzyl  alcohol,  577 
Berberine,  615 
Beta-derivatives,  588,  624 

-eucaine  hydrochloride,  607 

-naphthol,  588 
bcnzoate,  589 
-bismuth,  589 

-naphthylamine,  590 
Betaine,  620 
Bettendorf's  test,  354 
Bile,  684 

detection  in  urine,  737 
Biliary  acids,  685 

calculi,  686 

pigments,  684 
Bilirubin,  685 
Biliverdin,  685 
Bismark  brown,  567 
Bismuth,  327 

alloys,  327 

and  ammonium  citrate,  518 

beta-naphthol,  589 

citrate,  517 

nitrate,  328 

oxides  of,  327 

oxy-,  or  subcarbonate,  329 
or  subchioride,  330 
subnitrate,  328 
subsalts,  328 

subgallate,  586 

subsalicylate,  584 

tribrom-phenolate,  572 
Bismuthyl  salts,  328 
Biuret,  712 

reaction,  627 
Black  antimony,  358 

-ash,  263 

-lead,  178 

-wash,  337 

Bleaching-powder,  280 
Blood,  651 

coagulation  of,  653 

in  urine,  728 

occult,  691 

-pigments,  656 

plasma,  652 

-serum,  immune  bodies  of,  660 

-stains,  examination  of,  659 
Blue  mass,  336 

pill,  336 

Prussian,  301,  554 

stone,  325 

Turnbull's,  301,  555 

vitriol,  325 
Boiling,  52 


756 


INDEX. 


Boiling-point,  53 

determination  of,  54 

of  solutions,  161 
Bonds,  double  and  triple,  471 
Bone,  662 

-ash,  279 

-black,  279 

-oil,  590 
Borax,  187,  266 

glass,  266 

in  milk,  701 
Boroglycerin,  487 
Boron,  187 

trioxide,  187 

Botger's  bismuth  test,  731 
Boyle's  law,  26 
Brain,  670 
Brandy,  486 
Brass,  323 
Braunite,  303 
Bricks,  289 

Bright  line  spectra,  61 
Brimstone,  205 
Erin's  process,  138 
British  gum,  536 
Brittleness,  26 
Bromalin,  543 
Brom-ethane,  478 
Bromine,  239 

deci-normal  solution,  424 

iodide,  243 
Bromoform,  477 
Bromoformin,  543 
Bromol,  571 
Bronze,  323 
Brucine,  611 
Butter,  525,  698 

-milk,  695 

of  antimony,  360 

C. 

CACODYL,  478 

oxide,  478 
Cadaverine,  620 
Cadinene,  597 
Cadmium,  318  / 
Caesium,  267 

salts,  268 
Caffeine,  616 

citrated,  616 
Calamine,  312 
Calcined  magnesia,  273 

plaster,  279 
Calcium,  277 

acid  phosphate,  279 

bromide,  280 

carbide,  281 

carbonate,  278 

chloride,  280 

cyanamide,  553 

glycerin-phosphate,  489 

hydroxide,  278 

hypochlorite,  281 


Calcium  hypophosphite,  280 

oxalate,  508,  742 

oxide,  277 

phosphate,  279 

sulphate,  279 

sulphide,  281 

superphosphate,  279 
Calc-spar,  277 

Calculations,  chemical,  100,  111,  139 
Calculi,  biliary,  671 

fecal,  692 

urinary,  745 
Calomel,  338 

Caloric  value  of  foods,  642 
Calorie,  48 
Calorimeter,  49 
Camphene,  597 
Camphor,  598 

artificial,  596 

mint-,  599 

monobromated,  598 
Cane-sugar,  533 
Caoutchouc,  597 
Capillary  attraction,  37 
Caramel,  531 
Carat,  definition  of,  366 
Carbamide,  546,  710 
Carbide,  178 

aluminum,  466 

calcium,  281 
Carbinol,  479,  482 
Carbohydrates,  528,  729 

classification  of,  529 
Carbolic  acid,  569 

coefficient,  570 
Carbon,  178 

dioxide,  180 

ionic  explanation  of  liberation 
of,  195 

disulphide,  217 

monoxide,  183 

silicide,  186 

tetrachloride,  474 
Carbonic  oxide,  183 
Carbonyl  chloride,  184 
Carborundum,  186 
Carboxyl,  496 
Carboxylic  acids,  496 
Carbylamines,  555 
Carniferrin,  668 
Caryophyllene,  595 
Casein,  696 

silver-,  334 
Caseinogen,  696 
Catalysis,  154 
Cathode,  75,  82,  190 

rays,  83 

Cations,  83,  190 
Caustic,  lunar,  332 

mitigated,  332 

potash,  256 

soda,  262 
Cedrene,  597 
Celestite,  282 


INDEX. 


757 


Celluloid,  538 
Cellulose,  536 

nitrates  of,  537 
Celsius  thermometer,  46 
Cement,  290 

Centigrade  thermometer,  46 
Cerebrosides,  670 
Cerite,  291 
Cerium  oxalate, .  291 
Chains,  definition  of,  449 
Chalk,  277 
Charcoal,  animal,  280 

reduction  test,  212 
Charles'  law,  45 
Chelene,  478 
Chemical  affinity,  92 

calculations,  100,  111,  139 

changes  after  death,  649 

in  plants  and  animals,  639 

effects  of  light,  68 

energy,  91,  142 

equations,  definition,  110 
types  of,  113 

equilibrium.  114 

formulas,  99 

reaction,  definition,  92 

work,  142 
Chemistry,  analytical,  371 

definition  of,  18 

organic,  440 

physiological,  623 

thermo-,  143 
Chile  saltpeter,  266 
Chinoline,  593 
Chloral,  492 

hydrated,  493 
Chloralamide,  544 
Chloralformamide,  544 
Chlorate  of  potash,  258 
Chloride  of  lime,  280 

nitrogen,  243 
Chlorinated  lime,  280 

soda,  237 
Chlorine,  230 

compound  solution  of,  232 

iodides,  243 

oxides  of,  235 

water,  232 
Chloroform,  474 
Choke-damp,  184 
Cholesterin,  527,  671 
Choline,  620,  671 
Chondrin,  628 
Chondromucoid,  630 
Chondroproteins,  630 
Chromates,  discussion  of,  308 
Chrome  alum,  310 

-iron  ore,  306 

-yellow,  311 
Chromic  anhydride,  308 

chloride,  309 

hydroxide,  310 

oxide  or  sesquioxide,  309 

salts,  309 


Chromite,  306 
Chromium,  306 

and  ammonium  sulphate,  310 

and  potassium  sulphate,  310 

trioxide,  308 
Chyme,  674 
Cinchona  alkaloids,  608 
Cinchonidine,  610 
Cinchonine,  609    , 
Cineol,  599 
Cinnabar,  335,  342 
Cinnamic  aldehyde,  578 
Cinnamyl  acetate,  595 
Clay,  289 

Cleavage,  hydrolytic,  453 
Coagulases,  637 
Coal,  467 

-oil,  468 

-tar,  470 
Cobalt,  312 

blue  glass,  312 
Cocaine,  606 

substitutes,  580,  607 
Codeine,  613 

Coefficient  of  expansion,  48 
Cognac,  486 
Cohesion,  19 
Cohesive  gold,  365 
Colchicine,  617 
Collagen,  628 
Collargol,  331 

ointment,  331 
Collodion,  538 

medicated,  538 
Colloidal  silver,  331 

solution,  331 
Colloids,  41 
Colloxylin,  538 
Colophony,  599 
Color,  56 

Columbian  spirit,  482 
Combining  weights  of  elements,  95 
Combustion,  141 

spontaneous,  141 
Commutator,  78 
Complement,  661 
Compound  acetanilide  powder,  565 

definition,  88 

effervescing  powder,  515 

solution  of  cresol,  574 

spirit  of  ether,  522 
Conduction  of  heat,  49 
Conductivity,  197 
Conductors  of  electricity,  69 
Congo  red,  411 
Coniine,  604 

Constitutional  formulas,  123 
Contact  action,  154 
Convection,  50 
Copaiva  balsam,  599 
Copper,  323 

acetate,  504 
basic,  504 

aceto-arsenite,  504 


758 


INDEX. 


Copper  alloys,  323 

ammonio-compounds  of,  325 

arsenate,  352 

arsenite,  352 

oxides,  324 

carbonate,  325 

-glance,  323 

ions  of,  326,  327 

pyrites,  323 

sulphate,  325 
Copperas,  298 
Coproliths,  692 
Corpuscles  or  electrons,  85 
Corrosive  chloride  of  mercury,  339 

sublimate,  339 
Corundum,  286 
Cotarnine,  614 
Cotton,  collodion,  538 

medicated,  537 
Coumarin,  578 
Cream,  700 

of  tartar,  514 
Creatine,  546,  666 
Creatinine,  546,  666,  715 
Crede's  ointment,  331 

silver,  331 
Creolins,  574 
Creosol,  575 
Creosotal,  574 
Creosote,  574 

carbonate,  574 
Cresol,  574 

Critical  temperature,  141 
Cryoscopic  method,  160 
Crystal  systems,  22 
Crystallization,  20 
Crystalloids,  41 
Crystals,  20 

acicular,  25 

clinometric,  22 

laminar,  25 

orthometric,  22 

prismatic,  25 

tabular,  25 

Cupellation  of  gold,  364 
Cuprous      compounds,      remarks      on, 
323 

oxide,  324 
Curd,  700 
Currents,  alternating,  78 

dynamo-electrical,  78 

faradic,  79 

induced,  78,  79 

interrupted,  79 

magneto-electric,  78 

secondary,  79 
Cyanamide,  553 
Cyanides,  detection  in  poisoning,  552 

double  salts,  551 

organic,  555 
Cyanogen,  548 

complex  radicals  of,  553 

compounds,  547 

dissociation  of,  549 


Cyanogen    compounds    obtained   from 

atmospheric  nitrogen,  552 
Cymene,  564 
Cystine,  545,  720,  744 
Cystogen,  543 

D. 

DALTON'S  atomic  theory,  97 

Daniell's  cell,  75 

Daturine,  605 

Decay,  454 

Decomposition  by  electricity,  90 

heat,  87 

light,  90 

mutual  action  of  substances,  90 

with    formation    of   a   precipitate, 

116,  193 

volatile  product,  116,  194 
Decrepitation,  377 
Deflagration,  378 
Deliquescence,  152 
Denaturants,  485 
Denatured  alcohol,  485 
Density,  33 
Dental  alloys,  337 
Dentine,  664 
Deodorizers,  457 
Deoxidation,  147 
Deoxidizing  agents,  147 
Derivatives,  definition  of,  451 
Dermatol,  586 
Desiccator,  404 
Destructive  distillation,  453 
Detection  of  acids,  391 

special  remarks,  398 
Dextrin,  536 
Dextrorotation,  67 
Dextrose,  530 
Diads,  103 
Dialysis,  40 
Dialyzed  iron,  298 
Diamine,  169 
Diamino-benzene,  566 
Diamond,  178 
Diastase,  534 
Diazo-compounds,  567 

-reaction,  Ehrlich's,  568,  739 
Dichlor-methane,  474 
Dichromates,  discussion  of,  308 
Dicyandiamide,  553 
Dicyanogen,  548 
Diethylene  diamine,  543 
Diffusion,  40 

of  gases,  42 

rate  of,  for  different  substances,  40 
Digestion,  645,  672 

gastric,  674 

intestinal,  681 

salivary,  672 
Dimethyl  benzene,  563 
Dimorphism,  22 
Dionin,  614 
Dipentene,  597 


INDEX. 


759 


Diphenyl-amine,  566 
Disaccharides,  529,  533 
Disinfectants,  457 
Disinfection  by  formaldehyde,  491 
Dispersion  of  light,  59 
Displacement,  113 
Dissociation,  172 

electrolytic,  189 

of  acids  and  bases,  199 

of  formic  acid  and  its  homologues, 
507 

table  of  degree  of,  203 
Distillation,  53 

destructive,  453 

fractional,  462 
Dithymol-diiodide,  575 
Diuretin,  616 
Divisibility,  28 
Dolomite,  272 
Donovan's  solution,  351 
Double  decomposition,  113 

refraction,  63 

salts,  definition  of,  122 
Drinking-water,  149 
Drying  oils,  525 
Ductility,  26 
Dulcin,  581 

Dulong  and  Petit's  law,  107 
Dumas   method   for   determination   of 

nitrogen,  445 
Dyes,  aniline,  564 

azo,  567 
Dynamite,  488 

E. 

EARTH  metals,  286 

summary  of  tests,  292 
Earthenware,  289 
Ebonite,  598 
Ecgonine,  606 
Effervescence,  152 
Efflorescence,  152 
Ehrlich's  theory  of  immunity,  662 
Elasticity,  26 
Elastin,  628 
Electric  circuit,  76 

current,  76 

discharge  through  gases,  83 

energy,  72 

conversion  of,  80,  82 

furnace,  80 

induction,  71 

insulators,  69 

light,  82 

motors,  78 

poles,  75 

spark,  71,  83 

units,  76 
Electrical  machines,  71,  78 

potential,  76 

tension,  76 
Electricity,  69 

by  chemical  action,  74 


Electricity  by  magnet  ism,  77 

conductors  of,  (>!) 

current,  72 

duality  of,  70 

frictional,  69 

galvanic,  74 

nature  of,  72 

negative,  70 

positive,  70 

resinous,  70 

static,  71 

vitreous,  70 

voltaic,  74 
Electro-chemical  equivalents,  197 

series  of  metals,  198 
Electrodes,  75,  82 

polarized,  198 
Electrolysis,  82,  195 

electromotive   force   required    for, 
198 

secondary  changes  in,  196 
Electrolytes,  82 
Electrolytic  dissociation  theory,  189 

solution  tension,  319 
Electromagnetism,  77 
Electromagnets,  77 
Electromotive  force,  76 
Elements,  classification  of,  125 

combining  weights  of,  95 

definition,  88 

metallic,  247 

classification  of,  251 
derivation  of  names,  247 
melting-points,  248 
occurrence  in  nature,  250 
properties  of,  252 
specific  gravity  of,  249 
tune  of  discovery,  249 
valence  of,  250 

natural  groups  of,  125 

non-metallic,  126,  135 

derivation  of  names,  135 
time  of  discovery,  136 
valence  of,  136 

periodic  system  of,  128,  130 

physical  properties  of,  129 

relative  importance  of,  124 
Emanation,  87 
Emerald  green,  504 
Emery,  286 
Empirical  formulas,  446 

solution,  407 
Emulsin,  578 

Emulsion,  definition  of,  152 
Emulsions,  524 
Enamel,  664 
Endosmosis,  40 
Endothermic  actions,  91 
Energy,  19 

chemical,  142 
Enterol,  574 
Enteroliths,  692 
Enzymes,  456,  636 
Eosin,  582 


760 


INDEX. 


Epithelial  cells,  687 
Epithelium,  665 
Epsom  salt,  274 
Equations,  chemical,  110,  113 

thermal,  143 
Equilibrium,  chemical,  11'4 

ionic,  192 

effect   hi    chemical    reactions, 
192 

nitrogenous,  644 
Equivalence,  102 

Equivalents    of    volumetric    solutions, 
416,  419,  422,  426 

electro-chemical,  197 
Erepsin,  687 
Erythrite,  529 
Erythrose,  528 
Esbach's  albuminometer,  726 
Eserine,  616 
Essence  of  mirbane,  563 
Essential  oils,  594 
Esters,  518 
Ethane,  466 

halogen  derivatives,  477 
Ethene,  472 
Ether,  50,  520 

acetic,  522 

diacetic,  591 

ethyl,  520 

hydrobromic,  478 

luminiferous,  50 

methyl,  522 
-ethyl,  522 

nitrous,  523 

sulphuric,  520 
Ethereal  salts,  518 
Ethers,  518 

compound,  518 

mixed,  519 
Ethoxy,  586 
Ethyl  acetate,  522 

alcohol,  482 

amine,  620 

bromide,  478 

carbamate,  545 

chloride,  477 

iodide,  478 

nitrite,  523 

assay  of,  429 

oxide,  520 

para-amino-benzoate,  580 
Ethylene,  472 

dichloride,  472 

series  of  hydrocarbons,  472 
Eucalyptol,  599 
Eudiometer,  427 
Eugenol,  575 
Euphorin,  545 
Europhen,  574 
Evaporations,  52 
Exalgin,  566 

Excretion,  definition,  649 
Exothermic  actions,  91 
Expansion,  coefficient  of,  48 


Explosive  gelatin,  488 
Extension,  18 

Extraction,  definition  of,  157 
Extractive  matter,  650 
of  muscle,  666 

F. 

FAHRENHEIT  thermometer,  46 
Faraday's  laws,  197 
Fats,  523,  646 
Fatty  acids,  496 

oils,  523 
Feathers,  665 
Fecal  calculi,  692 
Feces,  689 

examination  of,  690 
Fehling's  solution,  730 

test,  730 
Feldspar,  286 
Fermentation,  455 
Ferments,  hydrolytic,  636 

organized,  455 

soluble  or  unorganized,  455 

unorganized,  636 
Ferrates,  296 
Ferric  acetate,  503 

ammonium  sulphate,  299 

chloride,  297 

tincture  of,  297 

citrate,  518 

hydroxide,  296 

with  magnesium  oxide,  296 

hypophosphite,  300 

oxide,  295 

phosphate,  300 

soluble,  300,  518 

pyrophosphate,  soluble,  300,  518 

subsulphate,  300 

sulphate,  299 

tartrate,  516 
Ferricyanogen,  554 
Ferripyrine,  592 
Ferrocyanogen,  554 
Ferro-manganese,  303 
Ferrous  acetate,  503 

ammonium  sulphate,  299 

bromide,  298 

carbonate,  300 

saccharated,  300 

chloride,  296 

hydroxide,  295 

iodide,  298 

oxide,  295 

phosphate,  300 

sulphate,  298 

exsiccated,  299 

sulphide,  298 
Fertilizers,  279 
Fibrinogen,  654 

Fineness  of  gold,  definition,  365 
Fire-damp,  184,  466 
Fixed  oils,  524 
Flame,  184 


1XDEX. 


761 


Flame  tests,  261,  379 
Flashing-point,  469 
Fleitmann's  test,  355 
Flowers  of  sulphur,  205 

of  zinc,  313 
Fluorescein,  582 
Fluorine,  244 
Fluor-spar,  244 
Food,  animal,  640 

composition  and  fuel  values,  642 

digestibility  of,  643 

plant,  638 
Force,  definition  of,  19 

vital,  439 
Formaldehyde,  490 

disinfection,  491 

in  milk,  701 

para-,  490 
Formalin,  490 
Formamide,  544 
Formin,  543 
Formulas,  constitutional,  123,  447 

empirical,  446 

graphic,  123,  447 

molecular,  99,  446 

rational,  447 

structural,  447 
Fowler's  solution,  349 
Fractional  distillation,  462 
Frauenhofer  lines,  62 
Freezing-mixtures,  44 

-point  method,  Raoult's,  109 

-points  of  solutions,  160 
Fructose,  532 

Functional  test  of  kidney,  740 
Fusel  oil,  486 
Fusion,  change  of  volume  by,  52 

latent  heat  of,  52 

-point,  51 

G. 

GALACTOSE,  532 
Galena,  318 

argentiferous,  330 
Gallacetophenone,  577 
Gall-stones,  671 
Galvanic  electricity,  76 
Galvanized  iron,  313 
Gamma  derivatives,  624 
Gas,  analysis  of,  427 

definition  of,  26 

elasticity  of  a,  26 

illuminating,  469 

laughing,  172 

natural,  467 

olefiant,  472 

tension  of  a,  26 

volume,  reduction  of  a,  428 

water-,  184 

Gases,  absorption  by  charcoal,  39 
by  liquids,  39 
by  platinum,  39 

diffusion  of,  42 


Gases,  ionic  explanation  of  liberation  of, 
194 

solution  of,  159 

weight  of,  34 
Gasoline,  468 
Gastric  digestion,  675 

juice,  674 

examination  of,  677 
Gay-Lussac's  law,  100 
Gelatin,  663 

-dynamite,  488 

explosive,  488 
German  silver,  323 
Germicides,  457 
Gin,  486 
Glass,  289 

borax,  266 

cobalt,  312 

soluble,  186 
Glauber's  salt,  264 
Gliadin,  628 
Globin,  657 
Globulins,  627 
Glonoin,  487 
Glucosan,  531 
Glucose,  530 
Glucosides,  539 
Glucusimide,  581 
Glue,  663 
Gluside,  581 
Glutelins,  628 
Glycerides,  524 
Glycerin,  487 

phosphates,  488 

trinitrate,  487 
Glycerites,  487 
Glycerol,  487 
Glycerose,  528 
Glycine,  544 
Glycocoll,  544 
Glycogen,  539,  692 
Glycols,  479 
Glycoproteins,  630 
Glycozone,  155 
Gmelin's  test,  685,  737 
Gold,  363 

alloys,  366 

and  potassium  cyanide,  364 

and  sodium  chloride,  366 

chlorides,  366 

cohesive,  365 

fineness  of,  365 

refining  by  cupellation,  364 
parting,  364 
quartation,  365 

Golden  sulphuret  of  antimony,  360 
Goulard's  extract,  504 
Graham's  law  of  diffusion,  42 
Gram-atom,  407 
Gram-molecule,  407 
Granite,  286 
Grape-sugar,  530 
Graphic  formulas,  123 
Graphite,  178 


762 


INDEX. 


Gravimetric  methods,  403 

Gravitation,  31 

Green  iodide  of  mercury,  340 

vitriol,  298 
Group-reagents,  382 
Guaiacamphol,  575 
Guaiacol,  575 

carbonate,  575 

derivatives,  575 

-salol,  575 
Guanidine,  546 
Guaranine,  616 
Gum  arabic,  536 

British,  536 

-resins,  599 
Gun-cotton,  537 

-metal,  323 
Gunpowder,  258,  538 

smokeless,  538 
Gutta-percha,  598 
Gutzeit's  test,  354 

modified,  354 
Gypsum,  279 


H. 


ELEMATIN,    657 

Hsematoporphyrin,  657 
Haematoxylin,  410 
Haemin  crystals,  659 
Haemoglobin    carbon    monoxide    com- 
pound, 657 
Haemoglobins,  631 
Haemolysis,  662 
Haine's  test,  731 
Hair,  665 
Halogens,  230 
Haptophore  group,  662 
Hardness,  25 
Hartshorn,  spirit  of,  169 
Hausmannite,  303 
Heat,  43 

bright  red,  48 

conduction  of,  49 

convection  of,  50 

dark  red,  48 

decomposition  by,  87 

effects,  45 

incipient  red,  48 
white,  48 

latent,  44 

mechanical  equivalent  of,  48 

of  neutralization,  203 

of  solution,  158 

radiation  of,  50 

rays?  50 

sources  of,  44 

specific,  49 

waves,  51 

white,  48 

yellow,  48 
Heavy  spar,  283 
Hedonal,  545 


Helianthin,  411 

Helium,  167 

Heller's  test,  626,  731 

Hematite,  293 

Hemiterpenes,  594 

Henry's  law,  159 

Hepar,  212,  378 

Heptads,  103 

Heroin,  613 

Hexads,  103 

Hexamethylenamine,  543 

Hexone  bases,  633 

Histidine,  630 

Histones,  629 

Holocaine  hydrochloride,  607 

Homatropine,  605 

Homologous  series,  450 

Hoofs,  665 

Hordein,  628 

Hornblende,  286 

Horns,  665 

Humidity,  165 

Humulene,  597 

Humus,  649 

Hydracids,  117 

Hydrastine,  615 

Hydrastinine,  615 

Hydrazine,  169 

Hydrazones,  568 

Hydrocarbons,  benzene  series,  561 

ethylene  series,  472 

general  remarks,  462 

halogen      substitution      products, 
473 

methane  or  paraffin  series,  464 

terpene  series,  594 

unsaturated,  470 
Hydrogen,  144 

arsenide,  350 

dioxide,  153 

nascent,  148 

peroxide,  153 

phosphide,  229 

phosphoretted,  229 

sulphide,  214 
Hydrolysis,  201,  453,  636 
Hydrolytic  cleavage,  453,  636 

ferments,  636 
Hydrometers,  34 
Hydroquinone,  576 

hydroxy-,  577 
Hydroxides,  119,  151 
Hydroxyl,  119 
Hydroxylamine,  169 
Hygrine,  606 
Hygrometers,  166 
Hygroscopic,  152 
Hyoscine,  606 
Hyoscyamine,  605 
Hypertonic  solutions,  163 
Hypnal,  592 
Hypochlorites,  237 
Hypotonic  solutions,  163 
Hypoxanthine,  668 


INDEX. 


7C3 


ICELAND  spar,  63 
Ichthyol,  573 
Illuminating  gas,  469 

oil,  468 

Imino-compounds,  542 
Immunity,  Ehrlich's  theory  of,  662 
Impurities,  detection  of,  433 
Indestructibility,  42 
India-rubber,  597 
Indican,  721 
Indicators,  410 

ionic  explanation  of  action,  411 
Indigo,  721 

-red,  722 
Indole,  693 
Indoxyl,  721 
Induction,  71 

coil,  79 

voltaic,  78 
Ink,  blue,  554 

indelible,  333 
Inosite,  532 
Internal  energy,  91 
Intestinal  digestion,  681 

sand,  692 
Inversion,  533 
Invertases,  637 
Iodide  of  nitrogen,  243 

sulphur,  243 
lodimetry,  421 
Iodine,  240 

chlorides  of,  243 

compounds  of  nitrogen,  244 

Lugol's  solution,  242 

pentoxide,  243 

sulphide  of,  243 

tincture  of,  241 

decolorized,  270 
lodoform,  477 
lodoformin,  543 
lodol,  591 
Ionic  equations,  192 

equilibrium,  192 

mechanism  of  solution,  217 
lonization  constant,  192 

theory  of,  190 
Ions,  75,  190 

composition  of,  190 

independence  of,  199 
Iridium,  368 
Iron,  292 

acetates,  503 

alloys,  294 

alum,  299 

and  ammonium  sulphates,  299 

and  potassium  oxalates,  510 

and  quinine  citrate,  518 

and  strychnine  citrate,  518 

bar-,  294 

bisulphide,  293 

bromide,  263,  298 


Iron  carbonate,  300 

saccharated,  300 

cast-,  293 

chlorides,  296 

citrate,  518 

dialyzed,  298 

galvanized,  313 

-group  of  metals,  292 

summary  of  tests,  316 

hydroxides,  293 

hypophosphite,  300 

iodide,  298 

monoxide  or  suboxide,  293 

ores,  293 

oxides,  293,  295 

oxychloride,  298 

perchloride,  297 

phosphate,  300 

soluble,  300,  518 

pig-,  293 

protochloride,  296 

pyrites,  293 

pyrophosphate,  soluble,  518 

reduced,  295 

rust,  294 

scale  compounds  of,  516,  518 

sesquichloride,  297 

subsulphate,  300 

sulphates,  298 

sulphide,  298 

tartrate,  516 

tersulphate,  299 

trioxide,  296 

wrought-,  294 
Isocholesterin,  527 
Isocyanides,  organic,  555 
Isomerism,  451 
Isomorphism,  22 
Iso-nitriles,  555 
Isonitroso  compounds,  540 
Isoquinoline,  593 
Is-osmotic  solutions,  163 
Isosulphocyanates,  556 
Isotonic  solutions,  163 


K. 


KAIRINE,  593 

Kaolin,  289 

Kelene,  478 

Kelp,  241 

Keratins,  628 

Kerosene,  468 

Ketones,  494 

Ketoses,  530 

Ketoximes,  541 

Kidney,  functional  test  of,  740 

Kieserite,  274 

Kinases,  638 

Kjeldahl    determination    of    nitrogen, 

445 

Koppeschaar's  solution,  424 
Krystallose,  581 


764 


INDEX. 


L. 

LABARRAQUE'S  solution,  237 
Lactalbumin,  696 
Lactoglobulin,  696 
Lactometers,  34 
Lactophenin,  572 
Lactose,  534,  699 
Lakes,  288 
Lanolin,  527 
Lapis  infernalis,  332 

lazuli,  290 
Lard,  525 
Latent  heat,  44 

of  fusion,  52 
of  vaporization,  54 
Laughing  gas,  172 
Laurinol,  598 
Law,  Avogadro's,  30 

Boyle's,  26 

Charles',  45 

Dulong  and  Petit's,  107 

Gay-Lussac's,  100 

Graham's,  42 

Henry's,  159 

Mariotte's,  26 

Mendelejeff's,  126 

Newton's,  31 

Ohm's,  77 

Raoult's,  161 

of  atomic  heats,  107 

of  combination  by  volume,  100 

of  constancy  of  composition,  93 

of  correlation  of  energies,  42 

of  equivalents,  102 

of  mass  action,  116 

of  multiple  proportions,  94 

of  specific  heats,  107 

of    the    conservation    of    energy, 

42 
Laws  of  electrolysis,  Faraday's,  197 

of  osmotic  pressure,  163 
Lead,  318 

acetate,  503 
basic,  503 
tribasic,  504 

alloys,  319 

arsenate,  350 

carbonate,  321 

chloride,  322 

chromate,  322 

dioxide  or  peroxide,  319 

group  metals,  318 

summary  of  tests,  344 

iodide,  321 

nitrate,  321 

oleate,  526 

oxide,  319 

phosphate,  322 

plaster,  526 

red  oxide,  319 

subacetate,  503 

sugar  of,  503 

sulphate,  322 


Lead  sulphide,  318 

-water,  504 

white,  321 

Leblanc's  process,  263 
Lecithins,  670 
Lecithoproteins,  631 
Legal's  test,  737 
Leucine,  546,  635,  744 
Leucomaines,  621 
Levorotation,  67 
Levulose,  532 
Lieberman's  reaction,  627 
Light,  56 

chemical  effects  of,  68,  90 

dispersion  of,  59 

infra-red,  56 

plane-polarized,  64 

rays,  57 

reflection  of,  57 

refraction  of,  58 

ultra-violet,  56 

waves,  56 
Lignin,  536 
Lignite,  467 
Lime,  277 

acid  phosphate  of,  279 

air-slaked,  277 

chloride  of,  280 

chlorinated,  280 

-kilns,  277 

liniment,  526 

milk,  of  278 

nitrogen,  553 

phosphate  of,  279 

sulphurated,  281 

superphosphate  of,  279 

-water,  278 
Limestone,  277 
Limonene,  597 
Liniments,  526 

Linkage,  double  and  triple,  471 
Lipase,  683 
Lipoids,  670 
Liquids,  absorption  of  gases  by,  40 

definition  of,  26 
Litharge,  319 
Lithium,  267 

benzoate,  580 

bromide,  267 

carbonate,  267 

citrate,  517 

hydroxide,  267 

phosphate,  267 

salicylate,  583 
Litmus  paper,  410 

solution,  410 
Liver,  function  of,  692 
Lodestone,  296 
Losophan,  574 
Lugol's  solution,  241 
Lunar  caustic,  332 
Lupulin,  486 
Lymph,  662 
Lysine,  628 


INDEX. 


765 


Lysins,  660 
Lysol,  574 


M. 


MAGNESIA  alba,  273 

calcined,  273 

milk  of,  273 
Magnesite,  272 
Magnesium,  272 

ammonium  phosphate,  742 

carbonate,  273 

citrate,  517 

nitride,  274 

oxide,  273 

sulphate,  274 

effervescent,  274,  517 
Magnetic  field,  74 

iron  ore,  73,  293 
Magnetism,  73 
Malachite,  323 
Malleability,  26 
Malonyl  urea,  547 
Malt,  534 
Maltose,  534 
Manganese,  303 

alloys,  303 

carbonate,  303,  306 

oxides  of,  302 

spar,  303 
Manganous  hydroxide,  306 

hypophosphite,  304 

sulphate,  304 
Mannite,  529 
Mannose,  532 
Mariotte's  law,  26 
Marsh-gas,  466 
Marsh's  test,  355 
Mass,  definition  of,  18 

-action,  law  of,  116 
Massicot,  320 
Matches,  safety,  222 
Matter,  action  of  heat  on,  28 

definition  of,  18 

fundamental  properties  of,  18 

radiant,  85 
Mayer's  solution,  601 
Measures,  metric,  32 
Meat-extracts,  669 
Mechanical  equivalent  of  heat,  48 
Meerschaum,  272 
Melanin,  739 
Melitose,  534 
Melting-point,  51 

determination  of,  52 
Membranes,  semipermeable,  162 
Mendelejeff's  periodic  law,  126 
Menthol,  599 
Mercaptans,  495 
Mercurial  ointment,  336 

plaster,  336 
Mercuric  ammonium  chloride,  342 

chloride,  339 

compounds,  remarks,  336 


Mercuric  cyanide,  551 
fulminate,  541 
iodide,  340 
nitrate,  341 
oxide,  337 

oxy-  or  subsulphate,  341 
and  potassium  iodide,  341 
and  sodium  chloride,  339 
salicylate,  584 
sulphate,  341 
sulphide,  335,  342 
Mercurous  chloride,  338 

compounds,  remarks,  336 
iodide,  340 
nitrate,  341 
oxide,  337 
sulphate,  341 
Mercury,  335 

ammoniated,  342 
and  arsenic  iodide,  351 
complex  salts  of,  345 
cyanide,  551 
fulminate,  541 
iodides,  340 
mass  of,  336 
mild  chloride  of,  338 
oxides  of,  337 
oxy  cyanide,  551 
proto-  or  subchloride  of,  338 
purification  of,  336 
salts,  action  of  ammonia  on,  343 
with  chalk,  336 
Meta-compounds,  559 
Metaldehyde,  492 
Metals,  247 

alkali-,  remarks  on,  255 

summary  of  tests,  272 
of  alkaline  earths,  277 

summary  of  tests,  285 
of  the  arsenic  group,  remarks  on, 
346 

summary  of  tests,  369 
classification  of,  251 
derivation  of  names,  247 
earth  group,  summary  of  tests,  292 
electro-chemical  series  of,  198 
iron  group,  remarks,  292 

summary  of  tests,  316 
lead  group,  remarks,  318 

summary  of  tests,  344 
manufacture  of,  253 
melting-points  of,  248 
noble  and  base,  253 
occurrence  in  nature,  250 
properties  of,  252 
remarks  on  tests  for,  274 
separation  of,  385 
specific  gravities  of,  249 
time  of  discovery,  249 
valence  of,  250 
Metamerism,  451 
Meta-phenylene-diamine,  566 
Metaproteins,  631 
Met-arsenites,  348 


766 


INDEX. 


Metathesis,  113 
Methaemoglobin,  657 
Methane,  466 

halogen  derivatives  of,  474 

series  of  hydrocarbons,  464 
Methoxy,  586 
Methyl  acetanilide,  566 

alcohol,  482 

amine,  620 

benzene,  563 

blue,  567 

chloride,  474 

ether,  522 

-ethyl  ether,  522 

-glycocoll,  545 

hydroxide,  482 

-orange,  410 

salicylate,  585 
Methylated  spirit,  482 
Methylene  azure,  567 

-blue,  566 

chloride,  474 

Methylthionine  hydrochloride,  566 
Mica,  286 
Microcidine,  589 
Microcosmic  salt,  380 
Milk,  694 

analysis,  701 

certified,  701 

changes  on  standing,  700 

clotting,  696 

cows',  695 

-fat,  698 

human,  702 

modified,  702 

of  lime,  278 

of  magnesia,  273 

of  sulphur,  205 

preservatives,  700 

-proteins,  696 

skimmed,  700 

-sugar,  534,  699 
Millon's  reaction,  626 
Mineral  waters,  149 
Minium,  320 
Mint-camphor,  599 
Mirbane,  essence  of,  563 
Mispickel,  347 
Modified  Gutzeit's  test,  354 
Mohr's  salt,  299 
Molecular  formulas,  99,  446 

motion,  43 

theory,  28 

weight,  definition,  99 

determination  of,  108 

weights,    relation    to    densities    of 

gases,  108 
Molecules,  99 
Molybdates,  368 
Molybdenum,  368 
Monads,  103 
Monazite  sand,  291 
Monosaccharides,  529 
Monsel's  solution,  300 


Moore's  test,  731 

Mordants,  288 

Morphine  and  its  salts,  612 

diacetyl-,  613 
Mortar,  278 

hydraulic,  290 
Mucins,  630 
Mucoids,  630 
Murexid  test,  716 
Muscarine,  671 
Muscle,  665 

extractives,  666 

sugar,  532 
Musculin,  666 
Mustard  oils,  556 
Mydatoxine,  621 
Mydine,  620 
Myosin,  666 
Myosinogen,  666 
Myrosin,  556 
Mytilotoxine,  620 

N. 

NAILS,  665 
Naphthalene,  587 

amino-,  589 

derivatives,  587 
Naphthol,  588 
Naphthylamines,  589 
Narceine,  614 
Narcotine,  614 
Nascent  hydrogen,  148 

state,  148 
Natural  gas,  467 
Nessler's  solution,  341,  374 

estimation  of  ammonia  by,  431 
Neuridine,  620 
Neurine,  620 
Neurodin,  545 

Neutral  substances,  definition  of,  120 
Neutralization,  119,  202 

equivalents,  416 

heat  of,  203 

ionic  explanation  of,  202 
Newton's  law,  31 
Nickel,  312 
Nicol's  prisms,  65 
Nicotine,  604 
Niter,  258 

cubic,  266 
Nitriles,  555 
Nitro-benzene,  563 

-cellulose,  537 

compounds,  540 

-glycerin,  487 

-phenols,  572 
Nitrogen,  164 

chloride,  244 

compounds  in  urine,  710 

determination  by  Dumas  or  abso- 
lute method,  445 
Kjeldahl  method,  445 
soda-lime,  445 


INDEX. 


767 


Nitrogen  iodide,  244 

oxides  of,  170 
Nitrolim,  553 
Nitrometer,  429 
Nitroso  compounds,  540 
Nitrous  ether,  523 

oxide,  172 
Nomenclature,  131 
Non-metallic  elements,  135 
Nordhausen  oil  of  vitriol,  212 
Normal  salt  solution,  physiologic,  656 

salts,  definition  of,  121 

solutions,  407 

equivalents  of,  416,  419,  422, 

426 

Nucleoproteins,  629 
Nutrition,  645 
Nylander's  reagent,  731 

0. 

OBERMAYER'S  test,  722 
Ohm,  76 
Ohm's  law,  77 
Oil,  bitter  almond,  578 
bone-,  590 
cinnamon,  595 

artificial,  578 
cloves,  596 
fusel,  486 
illuminating,  468 
of  garlic,  557 
of  vitriol,  208 
peppermint,  595 
phosphorated,  222 
turpentine,  596 
wintergreen,  585 
Oils,  drying  and  non-drying,  525 
essential  or  volatile,  594 
fatty,  523 
fixed,  523 
mustard,  556 
Oleates,  507 
Olefiant  gas,  472 
Olefins,  472 
Olein,  524 
Oleo-resins,  599 
Opalisin,  702 
Opium,  612 
Opsonins,  660 
Optic  axis,  63 
Optical  activity,  67 
Organic  chemistry,  440 

compounds,  action  of  heat  upon 

453 

classification  of,  460 
elementary  analysis  of,  442 
elements  in,  440 
general  properties    441 
various  modes  of    decomposi 

tion,  452 
cyanides,  555 
ispcyanides,  555 
Organized  ferments,  455 


Orphol,  589 
Orpiment,  347 
Ortho-compounds,  559 
Osazones,  530,  568 
Osmose,  40 
Osmotic  cells,  162 

pressure,  162 
Ossein,  628 
Oxalates,  509 
Oxalyl  urea,  547 
Oxidases,  637 

Oxidation,  definition  of,  141 
Oxides,  acid-forming  or  acidic,  117 

basic,  141 

definition  of,  141 

neutral,  141 
Oxidimetry,  417 
Oxidizing  agents,  142 
Oximes,  541 
Oxyacids,  117 
Oxygen,  137 
Oxy haemoglobin,  656 
Oxypurine,  715 
Ozone,  142 

thermochemistry  of,  144 

P. 

PAINTER'S  colic,  322 
Palladium,  367 
Palmitin,  524 
Pancreatic  juice,  682 

secretions,  682 

stones,  692 
Pancreatin,  638 
Paracasein,  696 
Para-compounds,  559 
Paraffin,  469 

series  of  hydrocarbons,  464 
Paraformaldehyde,  490 
Paraldehyde,  492 
Parchment  paper,  537 
Paris  green,  352,  504 
Parting  of  gold,  364 
Pasteurization,  701 
Pearl-white,  329 
Peat,  467 

Pelletierine  tannate,  608 
Pentads,  103 
Pental,  472 
Pentosanes,  735 
Pentoses,  orcin  reaction,  735 
Pepsin,  638 
Peptides,  633 
Peptones,  632 
Peria's  reaction,  635 
Perissads,  104 
Petrolatum,  469 
Petroleum,  468 

-benzin,  468 

Pettenkofer's  test,  686,  738 
Phellandrene,  597 
Phenacetin,  572 
Phenetidin,  572 


768 


INDEX. 


Phenetidin  derivatives,  572 
Phenol,  569 

amino-,  572 

coefficient,  570 

determination  in  urine,  722 

nitro-,  572 

titration  of,  424 

tri-brom-,  571 

trinitro-,  572 

Phenolphthalein,  410,  582 
Phenolsulphonphthalein,  582 
Phenoxy,  586 
Phenylacetamide,  565 

acrolein,  578 

-amine,  564 

hydrazine,  568 

salicylate,  585 
Phloroglucinol,  577 
Phosgene,  184 
Phosphides,  221 
Phosphine,  229 
Phosphoprotein,  630 
Phosphorated  oil,  222 
Phosphoretted  hydrogen,  229 
Phosphorite,  219 
Phosphorus,  219 

antidotes  to,  222 

detection  of,  222 

determination     in     organic     com- 
pounds, 445 

oxides  of,  223 

oxychloride,  229 

pentachloride,  229 

pills  of,  222 

red  or  amorphous,  221 

spirit  of,  222 

trichloride,  229 
Photography,  333 
Phthaleins,  582 
Phthalic  anhydride,  581 
Physical  properties  of  elements,  129 
Physics,  definition  of,  17 
Physiological  chemistry,  623 
Physostigmine,  616 
Pilocarpine,  604 
Pinene,  596 

hydrochloride,  596 
Piperazine,  543 
Piperidine,  543 
Piperin,  604 
Pitch-blende,  84 
Plant  food,  640 
Plaster,  calcined,  279 

lead,  526 

of  Paris,  279 
Platinic  ammonium  chloride,  367 

chloride,  367 
Platinum,  367 

alloys,  367 

and  barium  cyanide,  368 

black,  and  sponge,  367 

absorption  of  gases  by,  39 
Plumbago,  178 
Poirier's  orange  3P,  411 


Polariscope,  65 
Polarization,  63 
Polarized  electrodes,  198 
Polonium,  84 
Poly-amines,  543 
Polymerism,  451 
Polymorphism,  22 
Polysaccharides,  529,  535 
Polyterpenes,  594 
Porcelain,  289 
Porosity,  36 
Porter,  486 
Pot-metal  alloys,  254 
Potash,  bichromate  or  red  chromate  of, 
307 

caustic,  256 

chlorate  of,  258 

crude,  256 

red  prussiate  of,  555 

yellow  chromate  of,  307 

prussiate  of,  554 
Potassium,  255 

acetate,  503 

acid  or  bitartrate,  514 
oxalate,  509 

and  antimony  tartrate,  515 

arsenite,  349 

bicarbonate,  257 

bisulphate,  259 

bromide,  260 

carbonate,  257 

chlorate,  258 

chromate,  308 

citrate,  517 

cyanate,  553 

cyanide,  550 

dichromate,  307 

ferrate,  296 

ferricyanide,  555 

ferrocyanide,  554 

gold  cyanide,  364 

hydroxide,  256 

hypophosphite,  259 

iodide,  259 

iron  oxalates,  510 

manganate,  305 

mercuric  iodide,  341 

nitrate,  258 

oxide,  257 

percarbonate,  257 

perchlorate,  238 

permanganate,  305 

persulphate,  214 

sodium  tartrate,  515 

sulphate,  259 

sulphite,  259 

sulphocyanate,  553 

tartrate,  515 

tetroxalate,  509 
Powder  of  Algaroth,  360 
Precipitate,  definition  of,  116 
Precipitation,  definition  of,  121 

ionic  explanation  of,  193c 
Precipitins,  660 


769 


Preston  salt,  269 
Principle  of  Archimedes,  34 
Prismatic  spectrum,  59 
Prisms,  58 

Nicol's,  65 
Pro-enzymes,  638 
Prolamines,  628 
Proof-spirit,  484 
Propylamine,  620 
Protagon,  670 
Protalbumoses,  632 
Protamines,  629 
Protargol,  334 
Proteans,  631 
Proteases,  637 
Proteids.     See  Proteins. 
Proteins,  623 

alcohol-soluble,  628 

classification  of,  624 

coagulated,  632 

conjugated,  629 

decomposition  products,  633 

derived,  631 

simple,  625 
Proteolysis,  633 
Proteoses,  632 
Prussian  blue,  554 
Prussiate  of  potash,  red,  555 

yellow,  554 
Ptomaines,  617 
Ptyalin,  673 
Purine  bases,  667 
Putrefaction,  555 
Pycnometers,  34 
Pyocyanine,  620 
Pyramidon,  592 
Pyridine,  592 
Pyrites,  293 
Pyrocatechin,  575 

tests  for,  in  urine,  723 
Pyrogallol,  576 
Pyrolusite,  303 
Pyroxylin,  537 
Pyrozone,  155 
Pyrrol,  590 

tetra-iodo,  590 

Q 

QUANTIVALENCE,    102 

Quartation  of  gold,  365 
Quartz,  186 
Quick-lime,  277 
Quicksilver,  335 
Quinidine,  609 
Quinine,  608 

salts,  608 
Quinol,  576 
Quinoline,  593 

iso-,  593 

R. 

RADIATION  of  heat,  50 
Radical,  compound,  122 
definition  of,  122,  448 

49 


Radio-activity,  84 
Radium,  84,  284 

bromide  and  chloride,  285 
Raoult's  freezing-point  method,  161 
Rays,  Becquerel,  84 

cathode,  83 

of  heat,  50 

of  light,  57 

Rontgen,  83 

Reaction,  reversible,  114 
Reagents,  list  of,  374 

use  of,  in  analysis,  376 
Realgar,  347 

Reaumur  thermometer,  46 
Receptors,  662 
Recording  thermometers,  47 
Red  lead,  320 

prussiate  of  potash,  555 
Reduced  iron,  295 
Reducing  agents,  147 
Reduction,  147 
Reflection  of  light,  57 
Refraction,  double,  63 

of  light,  58 
Reinsch's  test,  353 
Rennin,  673 

Residue,  definition  of,  122 
Resins,  599 

gum-,  599 

oleo-,  599 
Resopyrine,  592 
Resorcin,  576 
Resorcinol,  576 

-phthalein,  582 
Respiration,  647 
Reticulin,  629 
Reversed  spectra,  62 
Reversible  actions,  114 
Reversion,  533 
Rhigolene,  468 

Rideal-Walker  coefficient,  570 
Rigor  mortis,  665 
Rochelle  salt,  515 
Rock,  phosphatic,  280 
Rodagen,  669 
Rontgen  rays,  83 
Rosaniline,  565 
Rosin,  599 
Rosolic  acid,  410 
Rouge,  296 
Rubber,  597 

preservation,  598 

vulcanized,  597 
Rubidium,  267 

salts,  268 
Ruby,  286 
Ruhmkorf  coil,  79 
Rum,  486 


SACCHARIN,  580 

soluble,  581 

Saccharinol,  581 


770 


INDEX. 


Saccharinose,  581 
Saccharol,  581 
Saccharose,  533 
Safety  matches,  222 
Safrol,  575 
Sal  ammoniac,  269 

sodse,  263 

volatilis,  269 
Salicin,  584 
Saliform,  543 
Salipyrin,  592 
Saliva,  672 
Salol,  585 
Salt  cake,  263 

common,  262 

of  lemon,  509 

of  sorrel,  509 

Preston,  269 
Saltpeter,  258 

Chile,  266 
Salts,  acid,  definition  of,  121 

basic,  definition  of,  121 

definition  of,  120 

double,  definition  of,  122 

ethereal,  518 

hydrolysis  of,  201 

ions  of,  201 

normal,  definition  of,  121 

reaction  to  litmus,  121,  201 

various  methods  of  obtaining,  120 
Salvarsan,  568 
Santolene,  597 
Santonin,  590 
Saponification,  525 
Sapphire,  286 
Sarcine,  668 
Sarcosine,  545 
Scale  compounds,  516 
Scheele's  green,  352 
Schiff's  reaction,  716 

for  formaldehyde,  490 
Schweinfurt  green,  352,  504 
Schweizer's  reagent,  537 
Scopolamine  hydrobromide,  606 
Secretin,  682 
Secretion,  definition,  649 
Sediment,  definition  of,  116 
Seidlitz  powders,  515 
Selenium,  217 

Semi-permeable  membranes,  162 
Serpentine,  272 
Sesquiterpenes,  597 
Sherer's  reaction,  636 
Shikimol,  575 
Shot  alloy,  347 
Silica,  186 
Silicates,  186,  286 
Silicon*  186 

carbide,  186 
dioxide,  186 
fluoride,  186 
Silver,  330 

allotropic  forms  of,  331 
alloys  of,  331 


Silver,  ammonio-chloride  of,  335 

compounds  of,  335 
bromide  and  iodide,  335 
-casein,  334 
chloride,  332 
colloidal,  331. 

complex  compounds  of,  334 
Crede's,  331 
cyanide,  551 
fulminate,  541 
German,  323 
mirror,  514 
nitrate,  332 

moulded,  332 
oxide,  333 
tartrate,  514 
vitellin,  334 
Sinigrin,  556 
Skatole,  693,  722 
Skeletins,  629 
Slag,  293 
Slate,  286 
Soap,  525 
Soapstone,  272 
Soda  ash,  263 
baking-,  264 
bichromate  of,  307 
caustic,  262 
-lime,  443 
washing,  263 
Sodium,  262 

acetate,  503 
-ammonium-hydrogen-phosphate, 

380 

arsanilate,  568 
arsenate,  349 
benzoate,  580 
bicarbonate,  264 
bisulphite,  264 
borate,  266 
bromide,  266 
cacodylate,  478 
carbonate,  263 

monohydrated,  264 
chlorate,  266 
chloride,  262 
citrate,  517 
cobaltic  nitrite,  374 
cyanide,  551,  553 
dichromate,  307 
glycerin-phosphate,  489 
and  gold  chloride,  366 
hydroxide,  262 
hypochlorite,  237 
hypophosphite,  266 
hyposulphite,  265 
ichthyo-sulphonate,  573 
iodide,  266 

mercuric  chloride,  339 
met-arsenite,  348 
metastannate,  363 
-naphthol,  588 
nitrate,  266 
nitrite,  266 


ISDEX. 


771 


Sodium  nitroferricyanido,  555 

nitroprusside,  555 

perborate,  189 

peroxide,  263 

phenolate,  570 

phenolsulphonate,  573 

phosphate,  265 

effervescent,  265 
exsiccated,  265 

potassium  tartrate,  515 

pyrophosphate,  265 

salicylate,  583 

stannate,  363 

sulph-antimonite,  359 

sulphate,  264 

sulphite,  264 

sulphocarbolate,  573 

tetrathionate,  213 

theobromine  salicylate,  616 

thiosulphate,  265 
Solder,  319 

Solids,  definition  of,  19 
Solubility,  definition  of,  158 

table  of,  396,  397 
Soluble  ferments,  455 
Solute,  158 
Solution,  colloidal,  331 

complex  or  chemical,  151 

definition  of,  151,  157 

heat  of,  158 

ionic  mechanism  of,  217 

of  gases,  159 

saturated,  151 

simple,  151 

tension,  319 

Solutions,  boiling-  and  freezing-points 
of,  160 

hyper-  and  hypotonic,  163 

is-osmotic  or  isotonic,  163 
Solutol,  574 
Solvay  process,  263 
Solveol,  574 
Somnoform,  478 
Sonnenschein's  test,  611 
Sources  of  heat,  44 
Sparteine,  604 
Spasmotpxine,  621 
Spathic  iron  ore,  293 
Specific  gravity,  32 

heat,  49 

weight,  32 
Spectroscope,  59 
Spectrum,  59 

continuous,  61 
Spermaceti,  520 
Spirit,  482,  486 

Columbian,  482 

methylated,  482 

of  ammonia,  aromatic,  269 

of  ether,  522 

compound,  522 

of  glonoin,  488 

of  glyceryl  trinitrate,  488 

of  hartshorn,  169 


Spirit  of  Mindererus,  503 

of  nitrous  ether,  523 
assay  of,  •}•_".) 

of  phosphorus,  222 

proof-,  484 

wood-,  482 
Stannic  chloride,  363 

hydroxide,  362 

oxide,  362 

sulphide,  363 
Stannous  chloride,  363 

hydroxide,  362 

oxide,  362 

sulphide,  363 
Starch,  535 

iodized,  536 

solution,  421 
Stassfurt  salts,  256 
Steapsin,  683 
Stearin,  524 
Stearoptens,  598 
Steatases,  637 
Steel,  294 

Stereo-isomerism,  452 
Sterilization,  458 
Stibnite,  358 
Stokes'  fluid,  657 
Stoneware,  289 
Storage  battery,  320 
Stout,  486 
Strontianite,  282 
Strontium,  282 

chloride,  bromide,  and  iodide,  282 

hydroxide,  282 

nitrate,  282 

oxide,  282 

salicylate,  584 
Strychnine,  610 
Stypticin,  614 
Sublimation,  21 
Substitution,  450 
Succus  entericus,  687 
Sucrates,  534 
Sucrol,  581 
Sugar,  cane-,  533 

estimation  in  urine,  733 

fruit-,  532 

grape-,  531 

muscle-,  532 

of  lead,  503 

of  milk,  534 
Sulph-antimonites,  359 

-arsenates,  351 
Sulpho-alcohols,  495 
Sulphonal,  495 
Sulphonethylmethane,  496 
Sulphonmethane,  495 
Sulphur,  204 

determination     in     organic     com- 
pounds, 445 

dioxide,  206 

flowers  of,  205 

iodide  of,  243 

milk  of,  205 


772 


INDEX. 


Sulphur,  oxides  of,  206 

precipitated,  206 

sublimed,  206 

trioxide,  208 

washed,  206 
Sulphurated  lime,  281 
Sulphuretted  hydrogen,  214 
Sulphuric  anhydride,  208 

ether,  520 

Sulphurous  anhydride,  206 
Supersaturation,  definition  of,  158 
Suprarenal  glands,  desiccated,  669 
Surface-action,  36 

tension,  38 

Sweet  spirit  of  niter,  523 
Sylvestrene,  597 
Symbols  of  compounds,  99 

of  elements,  99 
Synthesis,  151 

T. 

TABLE  of  solubility,  396,  397 

Talc,  272 

Tallow,  525 

Tannin,  585 

Tannon,  543 

Tannopin,  543 

Tartar,  665 

cream  of,  514 
crude,  512 
emetic,  361,  515 
Taurine,  546 
Tellurium,  217 
Temperature,  44,  46 
absolute,  47 
critical,  141 
kindling,  142 
Tempering,  252 
Tenacity,  26 
Tension,  26 

of  saturated  water-vapor,  53 
Terebene,  597 
Terpenes,  594 
Terpin  hydrate,  599 
Test,  charcoal  reduction,  212 

definition  of,  155 
Tests  for  acetanilide,  565 
acetic  acid,  503 
albumin  in  urine,  723 
aluminum,  290 
ammonium  compounds,  271 
antimony,  361 
antipyrine,  591 
apomorphine,  613 
arsenic,  351 
atropine,  605 
barium,  284 
bile,  in  urine,  737 
biliary  acids,  686 
pigments,  685 
bismuth,  329 
blood  in  urine,  728 
boric  acid  and  borates,  188 


Tests  for  brucine,  611 

calcium,  281 

carbohydrates  in  urine,  730 

carbonates,  183 

casein,  697 

chloral,  hydrated,  493 

chlorates,  238 

chloroform,  476 

cholesterin,  671 

chromium,  311 

cinchonine,  610 

citric  acid,  517 

cocaine,  607 

codeine,  614 

copper,  326 

creatinin,  667 

dextrose,  531 

ethyl  alcohol,  485 

fats  and  fatty  acids,  526 

ferrocyanides,  554 

fluorides,  244 

formaldehyde,  490 

gelatin,  664 

glycerin,  487 

glycogen,  693 

gold,  366 

hippuric  acid,  718 

hydrobromic  acid     and     bro- 
mides, 240 

hydrochloric    acid    and    chlo- 
rides, 234 

hydrocyanic  acid,  551 

hydrogen  dioxide,  155 

sulphide    and    sulphides, 
216 

hypochlorites,  238 

hypophosphites,  224 

indican,  721 

iodine  and  iodides,  242 

iron,  301 

lead,  322 

leucine,  635 

manganese,  305 

magnesium,  276 

mercury,  343 

metals,  remarks  on,  274 

metaphosphoric  acid,  226 

milk-sugar,  699 

morphine,  612 

nitric  acid  and  nitrates,  176 

nitrous  acid  and  nitrites,  173 

oxalic  acid,  509 

phenol,  571 

phosphates,  228 

phosphites,  225 

physostigmine,  617 

potassium,  260 

preservatives  in  milk,  701 

pyrocatechin,  723 

pyrophosphates,  226 

quinine,  609 

salicylic  acid,  584 

santonin,  590 

silicic  acid  and  silicates,  186 


L\DI-:X. 


773 


Tests  for  silver,  334 

simple  proteins,  626 
sodium,  267 
strontium,  282 
strychnine,  610 
sugar,  in  urine,  729 
sulphuric  acid  and  sulphates, 

211 
sulphurous  acid  and  sulphites, 

208 

tannic  acid,  586 
tartaric  acid,  514 
thiosulphates,  213 
tin,  363 
tyrosine,  635 
urea,  712 
uric  acid,  716 
veratrine,  611 
zinc,  315 
Tetanine,  621 
Tetrachlor-methane,  474 
Tetrads,  103 
Tetra-iodo-pyrrol,  591 
Tetronal,  496 
Thalleioquin,  609 
Thalline,  593 
Theine,  616 
Theobromine,  616 

sodium  salicylate,  616 
Theory,  atomic,  96 

of  equivalents,  102 
molecular,  28 
Thermal  equations,  143 
Thermo-chemistry,  143 
Thermodin,  545 
Thermometers,  46 
Thio-alcohols,  495 
Thiosinamine,  557 
Thymol,  575 

iodide,  575 
Thyreoidectin,  669 
Thyro-iodine,  242,  669 
Thyroid  glands,  desiccated,  669 
Tin,  362 

alloys,  323 
chlorides,  363 
hydroxides,  362 
oxides,  362 
perchloride,  363 
-plate,  362 
protochloride,  363 
-stone,  362 
sulphides,  363 

Tincture  of  ferric  chloride,  297 
of  iodine,  241 

decolorized,  270 
Titer,  412 
Titration,  403,  411 
Tollen's  orcin  reaction,  735 
Toluene,  563 
Tourmaline,  63 
Toxines,  619 

bacterial,  661 
endo-,  661 


Toxines,  soluble,  661 
Triads,  103 
Tribrom-methane,  477 
Trichloraldehyde,  492 
Trichlor-methane,  474 
Tri-cresol,  574 
Triiodo-methane,  477 
Trinitro-phenol,  572 
Trional,  496 
Triple  linkage,  471 
Trommer's  test,  730 
Tropseolin  D,  411 
Trypsin,  683 
Tryptophan,  684 
Turnbull's  blue,  301,  555 
Turpentine,  599 
Turpeth  mineral,  341 
Type  metal,  318,  358 
Typhotoxine,  621 
Tyrosine,  634,  744 
Tyrotoxicon,  621 

U. 

UFFELMANN'S  test,  669 

Ultramarine,  290 

Unguentum  Cred6,  331 

Urates,  742 

Urea,  546,  710 

compounds,  546 
determination  of,  712 
manufacture  of,  553 

Ureids,  547 

Ureometer,  Doremus',  714 

Urethane,  545 

Urinary  calculi,  745 
sediments,  740 

Urine,  703 

albumin  in,  estimation,  726 
alkaptonic  acids  in,  739 
ammonia  in,  estimation,  713 
analysis  of,  704 
carbohydrates  in,  729 
chlorides  in,  estimation,  719 
composition  of,  708 
estimation  of  sugar  in,  733 

Urinometer,  707 

Uritone,  543 

Urobilin,  705 

Urochrome,  705 

Uroerythrin,  705 

Urotropin,  543 

V. 

VALENCE,  102 
Vanillin,  578 

distinction  from  coumarin,  578 
Vaseline,  469 
Veratrine,  611 
Veratrol,  575 
Verdigris,  504 
Vermilion,  342 
Veronal,  547 


774 


INDEX. 


Vinegar,  502 
Vital  force,  439 
Vitriol,  blue,  325 

green,  298 

white,  315 
Volatile  oils,  594 
Volhard's  solution,  427 
Volt,  77 
Voltaic  electricity,  74 

induction,  78 
Volumetric  methods,  406 

solutions  equivalents  of,  416,  419, 

422,  426 
Vulcanite,  598 
Vulcanized  rubber,  597 
Vulcanizers,  80 

W. 

WASHING  soda,  263 
Wassermann  reaction,  662 
Waste  products  of  animal  life,  648 
Water,  148 

analysis,  429 

bitter  almond,  578 

of  crystallization,  152 

distilled,  150 

drinking-,  149 

-gas,  184 

hard,  149,  181 

lead-,  504 

mineral,  149 

soft,  149 

-vapor,  tension  of,  53 
Waves,  actinic,  56 

of  heat,  51 

infra-red,  56 

light,  56 

ultra-violet,  56 
Wax,  520 
Weight,  absolute,  32 

apparent,  32 

atomic,  definition  of,  98 

definition  of,  31 

specific,  32 

metric,  32 

molecular,  99 
Welsbach  mantle,  291 
Weyl's  reaction,  667 
Whey,  700 
Whiskey,  486 
White  arsenic,  348 

-lead,  321 


I  White  precipitate,  342 

vitriol,  315 
Widal's  reaction,  660 
Will-Varrentrap  determination  of  nitro- 
gen, 445 
Wine,  486' 
Witherite,  283 
Wood-naphtha,  482 

-spirit,  482 
Wool-fat,  527 
Work,  chemical,  142 

X. 

XANTHINE,  668 

alkaloids,  615 

bases,  667 

bodies,  717 

Xanthoproteic  reaction,  626 
Xeroform,  572 
Xylenes,  563 

Y. 

YELLOW  prussiate  of  potash,  554 
-wash,  338 

Z. 

ZEIN,  628 
Zinc,  312 

acetate,  503 

alloys,  313,  323 

amalgam,  313 

-blende,  312 

bromide,  314 

carbonate,  314 

chloride,  314 

flowers  of,  313 

hydroxide,  313 

iodide,  314 

oxide,  313 

oxy chloride,  314 

oxy phosphate,  314 

phenolsulphonate,  573 

silicate,  312 

sulphate,  315 

sulphocarbolate,  573 

valerate,  506 

-white,  313 
Zincates,  317 
Zingiberene,  597 
Zymogens,  638 


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Manual  of  chem 
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